THE PREPARATION OF SMALL METAL PARTICLES ON ZEOLITES AND OTHER SUPPORTS (MICROWAVES, MOESSBAUER, FISCHER-TROPSCH, FERROMAGNETIC RESONANCE)код для вставкиСкачать
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University Microfilms International 300 N. Zeeb Road Ann Arbor, Ml 48106 R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 8512151 M cM ahon, K erry Charles THE PREPARATION OF SMALL METAL PARTICLES ON ZEOLITES AND OTHER SUPPORTS Ph.D. The University of Connecticut University Microfilms International 1985 300 N. Zeeb Road, Ann Arbor, Ml 48106 Copyright 1985 by McMahon, Kerry Charles All Rights Reserved R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. PLEASE NOTE: In all cases this material has been filmed in the best possible way from the available copy. Problems encountered with this document have been identified here with a check mark V 1. 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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. THE PREPARATION OF SMALL METAL PARTICLES ON ZEOLITES AND OTHER SUPPORTS Kerry Charles McMahon, Ph.D. The University of Connecticut, 1985. Small metal particles selective catalysts for in the cages of the zeolites can be production of hydrocarbons from carbon monoxide and hydrogen. Our research involves several preparation of different methods for the particles of metal in zeolites. small Iron and cobalt were the metals investigated. Success microwave has been induced achieved argon plasma carbonyls and organometallics to metal particles. their chemical, Fischer-Tropsch through which the use decomposes of a metal form small ferromagnetic Characterization of these samples as to physical synthesis and catalytic properties has been done. for Details preparations and reactions are presented. R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. of Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. THE PREPARATION OF SMALL METAL PARTICLES ON ZEOLITES AND OTHER SUPPORTS Kerry Charles McMahon B.S., Geneva College, 1979 A Dissertation Submitted in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy at The University of Connecticut 1985 R eproduced with perm ission o f the copyright owner. F urther reproduction prohibited w itho ut perm ission. APPROVAL PAGE Doctor of Philosophy THE PREPARATION OF SMALL METAL PARTICLES ON ZEOLITES AND OTHER SUPPORTS Presented by Kerry Charles McMahon, B.S. Major Adviser_ Steven L. Suib Associate Adviser John Tanaka Associate Adviser Robert G. Michel The University of Connecticut 1985 - ii - R eproduced w ith perm ission o f the copyright owner. F urther reproduction prohibited w itho ut perm ission. Copyright by Kerry Charles McMahon 1985 R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. To Rete and Babum, R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. ACKNO W LEDGEM ENTS First of into all, I ’d like to chemistry and graduate school. I'd like to thank the Lord who helped me led me through undergraduate and He was always there when I needed Him. thank Steve for guiding me into a chemist. and molding me I appreciate all the extra effort he put into directing the research group. A special thanks goes to Dr. Tanaka whose late night advice helped me get my dissertation done. I'd also like to thank Dr. Michel for helping me with my dissertation. I want to say thanks to the entire Suib group from Ovid, Dimitri and Dan to Katy, Ann, Rich, Art, Jim, Norma, Zong-Chao, Janet and the unforgetable Mr. Willis. You made the four and a half years bearable. I want to thank Lennox Iton for exposing me to zeolite synthesis and making Argonne a fun experience. Finally, I'd like to thank my wife, Minnie, support, love and patience she has given me. for the I did it all for her. R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. Funding for this and other term of my dissertation was work carried out during the provided by the following agencies: Atlantic Richfield Foundation of the Research Corporation, Petroleum Research Fund of the American Chemical Society, National Science Foundation under Grant CHE 82 ^ 1 7 , Department of Energy, Basic Energy Sciences, and The University of Connecticut Research Foundation, Dissertation Fellowship. R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. TABLE OF CONTENTS APPROVAL P A G E .......................................... ii ACKNOWLEDGEMENTS ....................................... iv Chapter page I. INTRODUCTION ..................................... 1 O v e r v i e w ................................................ 1 B a c k g r o u n d Of T h e W o r k ............................. 2 ................... 2 Transition Metal Compounds S u p p o r t e d M e t a l C a t a l y s t s ..................... 2 H e t e r o g e n e o u s C a t a l y s i s ........................ 3 Spectroscopic Studies of Catalysts . . . . 5 Relevant Literature ................................ 6 Zeolites ........................................... 6 Zeolite Synthesis ........................... 6 Zeolite Structure ........................... 7 E x c h a n g e a b l e C a t i o n s ........................ 13 New Z e o l i t e s ........................... 15 P r e c u r s o r s Of S u p p o r t e d M e t a l s . . . . . . M e t a l L o a d e d Z e o l i t e s ......................... 26 I r o n L o a d e d Z e o l i t e s ....................... 26 C o b a l t L o a d e d Z e o l i t e s ..................... M e t a l A t o m V a p o r i z a t i o n ..................27 Bimetallic Zeolites ........................ I r o n An d C o b a l t On O t h e r S u p p o r t s ......... 29 M e t h o d s o f A c t i v a t i o n Of S u p p o r t e d M e t a l s . T h e r m a l A c t i v a t i o n ........................... Chemical Activation ........................ P h o t o c h e m i c a l A c t i v a t i o n ................... M i c r o w a v e A c t i v a t i o n ........................ F i s c h e r - T r o p s c h S y n t h e s i s ..................... S h a p e S e l e c t i v i t y ......................... 38 C a t a l y s t A c i d i t y ............................ 38 I n s t r u m e n t a l T e c h n i q u e s W h i c h AreU s e f u l . . . Methods For Pro bing E lect ro n ic P r o pe rt ie s . M o s s b a u e r S p e c t r o s c o p y . ................... Ferromagnetic Resonance ................... Infrared Spectroscopy ..................... Methods For Probing StructuralProperties . Electron Microscopy ........................ X-ray Powder Diffraction . . . . . . . . Me th ods For Probing Chemical Properties . . C-as C h r o m a t o g r a p h y ......................... 49 - vi - R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 18 27 28 30 30 33 33 34 35 39 39 39 45 48 48 48 49 49 Gravimetric Techniques ................. U9 R a t i o n a l e .......................................50 Catalyst Synthesis ........................ 50 Catalytic Reactions ........................ 51 Spectroscopic Characterization ........... 51 F o c u s ........................................... 52 II. EXPERIMENTAL METHODS ............................ 53 Introduction ................................... 53 Mossbauer Spectroscopy ........................ 53 Electron Paramagnetic Resonance/Ferromagnetic R e s o n a n c e ................................ 56 .......................... 56 Electron Microscopy X-ray Powder Diffraction ...................... 57 Infrared Spectroscopy ........................ 57 Gas C h r o m a t o g r a p h y .............................. 57 Thermal Analysis Techniques ................. 60 Microwave Generator .......................... 60 R e a g e n t s ......................................... 60 Sample Preparation M e t h o d s ..................... 62 Iron Carbonyl Zeolites .................... 62 Hydrogen Reductions ........................ 65 Sodium Vapor Reductions .................... 66 Bimetallic Zeolite Preparations ........... 69 New Aluminoferrisilicate Zeolite Preparations ........................ 69 Microwave Discharge Preparations.. ......... 73 Microwave Generation of Color Centers . . . 78 Inert Atmosphere Dry Box Procedures . . . . 79 Fischer-Tropsch Reactions ................. 79 III. R E S U L T S ............................................. 82 Investigations of Samples By Fischer-Tropsch R e a c t i o n s ................................ 82 Catalysts Prepared By Microwave Reduction . 82 Cobalt Catalysts ........................ 82 Iron C a t a l y s t s ............................88 Catalysts Prepared By Hydrogen Reduction 103 Iron Carbonyl Catalysts ............. 103 Bimetallic Zeolite Catalysts ......... 109 Spectroscopic Characterization of Catalysts 117 Catalysts Prepared By Microwave Reduction 117 Catalysts Prepared By Hydrogen Reduction 128 Iron Carbonyl Catalysts ............. 128 Bimetallic Zeolites ................. 1^1 Aluminoferrisilicate Zeolites . . . . 1^8 Catalysts Prepared By Sodium Vapor R e d u c t i o n ............................. 159 - vii - R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. IV. D I S C U S S I O N ..................................... 164 Fischer-Tropsch Results ................... 164 Catalysts Prepared By Microwave Reduction 164 Cobalt Catalysts ...................... 164 Iron C a t a l y s t s ...........................166 Catalysts Prepared By Hydrogen Reduction 169 Iron Carbonyl Catalysts ............. 169 Bimetallic Catalysts ................. 171 Spectroscopic Charaterization Of Catalysts . 173 Catalysts Prepared By Microwave Reduction 173 Catalysts Prepared By Hydrogen Reduction 177 Iron Carbonyl Zeolites ............... 177 Bimetallic Zeolites ................. 180 Aluminoferrisilicate Zeolites . . . . 183 Catalysts Prepared By Sodium Reduction . 184 Comparison of Sample Reduction Methods . . . 185 Completeness of Reduction ............... 185 Length of Reduction T i m e .................. 187 Comparison of Particle S i z e .................. 188 Mechanisms of Reduction of Metal Complexes in Z e o l i t e s ...........................191 Comparison to Zeolite Catalysts Prepared by O t h e r s ................................... 193 V. C O N C L U S I O N S ........................................ 196 Information Gained .......................... 196 Future Experiments .......................... 197 Catalytic Studies ........................ 197 Characterization Studies ............... 197 New P r e p a r a t i o n s ...........................198 R E F E R E N C E S .............................................. 201 VITA 213 - vi i i - R eproduced with perm ission o f the copyright owner. F urther reproduction prohibited w itho ut perm ission. L IS T OF T A B L E S Table P age 1. Description of Z e o l i t e s ............................ 11 2. Zeolite Properties ................................. 3. Mossbauer Data For Iron C o m p o u n d s ................. 41 4. Electronic Configurations of Iron and Cobalt . . . 47 5. Weight Percent Values 59 6. Vaporization Temperatures of Na and K 7. Synthesis Conditions ............................... 71 8. Reactant Concentrations 72 9. Catalytic Properties of Iron and Cobalt Catalysts 10. Catalytic Properties of Bimetallic Samples . . . 11. Values of g A p p a r e n t ............................... 127 12. Iron Carbonyl Samples, Unreduced ............... 129 13. Iron Carbonyl Samples, Reduced .................. 131 14. Bimetallic Samples, Unreduced .................. 14? 15. Bimetallic Samples, Reduced .................... 144 16. Aluminoferrisilicate Zeolites, Mossbauer Results 150 17. Mb'ssbauer of Reduced Aluminoferrisilicates . . . 152 18. Ion-Exchanged Zeolites, Mossbauer Results ... 160 19. Mossbauer Results After Sodium Reduction . . . . 162 20. Comparison of Reduction Methods 190 21. Comparison of Catalysts With Literature 12 ............................ ............. 68 .......................... 99 116 ................ . . . . - ix - R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 195 L IS T OF F IG U R E S Figure page 1. Structure of Zeolite X ............................... 9 2. Sites in Z e o l i t e s ................................... 14 3. Zeolite Framework Replacement 4. Structure of Fe(CO)c .................................19 D 5. Structure of Fe2 (C0 ) g .............................. 20 6. Structure of Co2 (C0 ) g .............................. 22 7. Structure of F e r r o c e n e .............................. 24 8. Structure of Nitroprusside Anion .................. 25 9. Mossbauer Experiment ............................... 43 10. In-situ Mossbauer C e l l .............................. 55 11. Inverted U T u b e ..................................... 64 12. Sodium Vapor Reduction Apparatus .................. 13* Sample T u b e ......................................... 74 14. Microwave L i n e ....................................... 76 15. Reaction L i n e ....................................... 81 16. Percent Conversion Cobalt Catalysts 17. Co Catalysts Methane Production .................. 85 18. CoZSM-5 Product Distribution ...................... 86 19. CoX Product D i s t r i b u t i o n ............................ 87 20. Percent Conversion of Iron on A .................... ............. 17 67 84 .................... 89 21 . Percent Conversion of Iron onZ S M - 5 ................ 91 - x - R eproduced w ith perm ission o f the copyright owner. F urther reproduction prohibited w itho ut perm ission. 22. Catalytic Properties of Iron onZ S M - 5 .............. 92 23. Percent Conversion of Iron on X 24. Catalytic Properties of Iron on X 25. Percent Conversion of FeX S i n t e r e d ................. 97 26. Percent Conversion of Iron on Y 27. Catalytic Properties of Iron on Y 28. Catalysis of Fe(C0)5Y 29. Methane and Ethane Production of Fe(C0)^Y 30. ftp Desorption of F e ( C 0 ) ^ Y ......................... 108 31. Catalytic Properties of C o Y ................ 111 32. CoY Activity Versus Temperature 112 33* Catalytic Properties of R u Y .................... 11 if ....................94 .................. 95 ................... 101 ................. 102 ..............................104 . . . ................ 106 3*1. RuY Reaction and Helium P u r g e ..................... 115 35. FeY FMR S p e c t r a .................................... 118 3 6 . FeY g Value Versus T e m p e r a t u r e ..................... 120 37. FeY FMR Linewidth Versus Temperature ............ 121 38. FMR of C o X ........................................... 123 39. CoX g Value Versus T e m p e r a t u r e .................. 12-4 40. CoX Linewidth Versus T e m p e r a t u r e ...................125 41. Mossbauer Spectrum of Fe(C0)^Y... ................ 42. TEM of Fe(CO)cY 0 43. Mossbauer of Fe(C0),-Y C a r b i d e ..................... 139 44. Mossbauer Spectrum of C o Y ......................... 146 45. DTA of A l u m i n o f e r r i s i l i c a t e ....................... 154 46. DTA of A l u m i n o f e r r i s i l i c a t e ....................... 155 47. FMR of A l u m i n o f e r r i s i l i c a t e ....................... 157 48. FMR of A l u m i n o f e r r i s i l i c a t e ....................... 158 132 .................................... 136 - xi - R eproduced with perm ission o f the copyright owner. F urther reproduction prohibited w ith o u t perm ission. Chapter I INTRODUCTION 1.1 OVERVIEW The research the study of described in transition this dissertation metals supported on involves zeolites. Several different methods were used to prepare and charac terize small metal particles (less the pores of zeolites. than 11 Angstroms) in Samples prepared by various meth ods were studied as catalysts in the Fischer-Tropsch reac tion. The goals of this research were to synthesize novel supported metal systems, Tropsch catalysts, and to to prepare selective to study various activation procedures investigate the chemical, properties of small Fischer- metal physical particles. and catalytic Throughout this work, several spectroscopic experiments were used to char acterize these metal supported zeolite catalysts before, during and after catalytic reactions. R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 2 1.2 BACKGROUND OF THE WORK 1.2.1 Transition Metal Compounds Transition metals, which include elements like iron, cobalt, ruthenium, etc., have very interesting properties. Some of these properties of transition metal compounds are various coordination geometries, variable oxidation states and the ability to form brightly colored compounds. sition metals are also important as catalysts. Tran Catalysts are materials that speed up reactions but are not signifi cantly consumed in the reaction. 1.2.2 Supported Metal Catalysts Transition metals when in a often act as supported metal form. system that results when a catalysts particularly A supported metal is a transition metal is dispersed on an inert material (support) such as Si02 or Al^O^. El ements can be used as supports, the most common being car bon. Oxides, such as alumina (A1?0^), silica (SiO? ) titania (Ti02 ) are also commonly used. and Zeolites are an other oxide material that can be used as a support. Dif ferent supports have different loading capacities, differ ent surface areas and different degrees of acid or base character. Because these metals are of the metal is small and dispersed, the particle size the surface area is large since R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 3 surface area is inversely related to particle size. One way to obtain a highly dispersed metal is to prepare a mo lecular cluster of metal cluster compound. atoms which is called a metal Metal clusters are compounds containing two or more atoms of the same or different metals usually with metal-metal bonds and ligands attached. The relationship between clusters has been suggested supported ported metals have those of metal clusters. characteristics of metals such also have similar characteristics clusters which have only a few metal magnetic properties than bulk supported metals 1 -ii exist between the prop Sup to metal atoms and different materials. may illuminate the Sup as the absence of attached groups and zero oxidation state. ported metals metal by Muetterties and others There are some relationships that erties of bulk metals and metals and The study of relationship between metals and metal clusters and improve theories about bond ing and catalytic reactions. 1.2.3 Heterogeneous Catalysis Present theories catalysts, lysts. suggest that there homogeneous catalysts Homogeneous catalysts are are two types of and heterogeneous cata used when the catalyst and reactants are in the same phase such as liquids react ing with a catalyst dissolved in solutions. Heterogeneous R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. u catalysts incorporate different phases such as a solid ca talyst and gaseous reactants. tion deals with heterogeneous catalysis, the initial The work in this disserta systems. In heterogeneous step is often the adsorption (or physical binding) of the reactants onto the active site or metal. The reaction takes place on the surface and then the products desorb from the catalyst. detach from a surface. To adsorb To desorb means to means to attach to a surface. The products that are formed lyst are self. governed by the and desorb from the cata properties of the The activity of the catalyst catalyst speeds up a reaction. lectivity which is is the rate that the The how much total product is formed. catalyst it activity determines The catalyst has a se the ability of a catalyst to form the desired product rather than several side products. Transition metals can speed up reactions such as the Fischer-Tropsch reaction which is the production of hydro carbons from hydrogen and carbon monoxide. We have pre pared supported metal catalysts that are active and selec tive Fischer-Tropsch catalysts. heterogeneous catalytic reactions tions which involves the bons from olefins Other important are hydrogenation reac formation of saturated hydrocar and the oxidation of ammonia by oxygen to form nitric oxide". R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 5 The properties factors that are the active caused by the shape sites. sition metal also of catalysts are affected In many The oxidation cases active sites activity and are tran Electronic factors selectivity of states of transition sponsible for the tion. and distribution of atoms on the catalyst. affect the by geometric catalysts. metals are electronic effect in a often re catalytic reac Many studies of supported metals appear in the lit erature. Several of these studies will be discussed in sections 1 .3*3 and 1.3 .^. 1.2.4 Spectroscopic Studies of Catalysts Heterogeneous catalytic reaction cult to understand. One of the mechanisms are diffi main features of our re search is the characterization of catalysts before, during and after a catalytic reaction. Several spectroscopic methods can be used to probe the geometric, electronic and catalytic properties of these systems. structural studies were done with diffraction and scanning Our geometric or the use of X-ray powder electron microscopy methods. Electronic properties were probed with Mossbauer spectros copy and electron resonance) flow paramagnetic resonance techniques. reactors and Catalytic reactions were done in the products chromatography and mass (ferromagnetic were analyzed with spectrographic methods. gas Further background information can be found in section 1.3* R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 6 1.3 RELEVANT LITERATURE 1.3.1 Zeolites One type of zeolite. con, oxide that can be used as a support is a Zeolites are aluminosilicates composed of sili aluminum and oxygen atoms. They were first discov ered in 1756 by Baron Cronstedt, a mineralogist of Swedish birth.^ Since that time, many uses have been found for 7 zeolites from replacement for phosphates in detergents to 7 abrasives in toothpaste . Several potential uses of zeolQ ites have also been suggested . stedt discovered existed in The zeolites that Cron nature. Naturally occurring zeolites are given names such as faujasite and chabazite. Other zeolites are man made. Man-made zeolites are given names such as A, X and ZSM-5. Some synthetic zeolites like Zeolon, marketed by the Norton Company, analogs such as mordenite. unique. have natural Other synthetic zeolites are The study of man-made zeolites involves the area of zeolite synthesis. 188.8.131.52 Zeolite Synthesis There are many ites Q-1 2 . patents concerning the synthesis Zeolites claves which are synthesized in high pressure reactors usually of stainless steel. high temperatures are typically of zeoiauto made out Synthesis conditions normally involve (150°C and (above one atmosphere). above) and high pressures These conditions mimic the condi R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. tions in which zeolites are formed in nature. occurring zeolites are usually found oceans. ammonium bromide, The factors near volcanoes or in Synthetic procedures often incorporate the use of templates which are organic form. Naturally around which the zeolite size of the template that determines formed. molecules such as tetrapropyl structures molecule is one the particular of the zeolite that is Zeolites are often crystallized from basic solu tions and the pH of the of the synthesis. nate phases phase is solution is a very important part Variations in in the zeolite. pH can introduce alter The preparation of usually desired. Variations in procedures can result in the a pure the synthetic preparation of zeolites with different structures. 184.108.40.206 Zeolite Structure Zeolites have structure. rahedra of an open three SiO^ and AlO^ units joined by the sharing of Theories about how these groups can attach 13 to each other have been suggested'-'. 13 framework They are formed by the vertex linking of tet- oxygen atoms. stein dimensional proposed that unstable and therefore A1 - 0 for instance, Lowen- - A1 bonds in do not exist - 0 - A1 bonds are much more stable. A 1C>2 unit has a charge of minus a charge of zero. A1 - 0 In _ zeolites are in the framework. Si This is because the one and the SiO^ unit has - Al, the minus charges are R eproduced w ith perm ission o f the copyright owner. F urther reproduction prohibited w itho ut perm ission. 8 too close together and repel each other making the struc ture unstable. Al, sion. In Si - 0 - there is no such repul Si - 0 - Si bonds are also stable because there is no repulsion. A specific structure, that of zeolite X, is shown in Figure 1. R eproduced w ith perm ission o f the copyright owner. F urther reproduction prohibited w itho ut perm ission. 9 Figure 1: Structure of Zeolite X Tetrahedral Si 0/ u R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 10 The three dimensional structure of the one for zeolite X, space which can contains such as a large amount of void be filled by molecules of species like metal carbonyls. sorption of a zeolite, molecules such have been reported water or other Several examples of the ab as volatile carbonyl species 14-22 The specific zeolite structure can affect the environ- 3+ 4+ ment of the A1J and Si ions in the framework structure. Solid state magic angle spinning nuclear magnetic resoO *3—O fc\ nance has been used to study these affects. These studies have involved the study of 27 A1 and observe the different A1 and Si environments environments can be different because of 29 Si 27-42 . NMR to These various zeolite compositions. The composition of zeolites is tion of a few common well known. zeolite types and can be found in Table 1. A tabula their structures A list of some of the properties of these zeolites is given in Table 2. R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 11 TABLE 1 Description of Zeolites Type A Unit Cell Composition Symmetry Na12(Al02 )12(Si02 )124.5H2 0 C Y Na5 6 (Al02 )56(Si02 )136250H2 0 c c M Na8 (A102 )g(Si02 )4024H20 0 NanAlnSi96_n019216H20 T X ZSM-5 44 formulas of A, X, Y and M from Breck ZSM-5 formula from Kokotailo and coworkers M - mordenite C - cubic 0 - orthorhombic T - tetragonal R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 12 TABLE 2 Zeolite Properties Type Pores(A) Stability(-K)— Largest AdsorbateDb A it.2 973 ethylene X 7.5 1045 (CifH9 )3N Y 7.5 1066 (c1|h9 )3n M 7.0 1273 ZSM-5 5.5 C6H6 — liq a from J a c o b s ^ b from Breck M - mordenite R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 13 Several good books are available that 7 in -iifi properties and structure ’ J of zeolites great deal and modified 5 8-55 penments J are a The chemical properties zeolites have of attention. X-ray diffraction studies . discuss zeolite also received Infrared investigations lie-8? a 217 48 ’ , and electron microscopy ex- few of the areas that have been ex tensively studied. 1.3*1*3 Exchangeable Cations One feature of zeolites which is highly related to the structure and the Si/Al ratio is the presence of exchange able cations. Cations are present aluminosilicate framework has an in zeolites since the overall negative charge. The general formula for a zeolite is the following^: M e X / n ( A 1 0 2 > X ( S 1 0 2 > y ‘M H 2 0 where Me can be a variety an overall charge ygen is -2. of -1. of cations.The SiO? of zerosince silicon is +H and unit has each ox The AlO^ unit, however, has an overall charge In oxides, A1 is usually +3 and each oxygen is -2. This negative charge is compensated by a cations can be monovalent lency (Ca 2+ 2+ , Mg ,A1 cation. These (Na+ , K+ , etc.) or of higher va- 3+ , etc.). Some of the possible ex change sites in a zeolite are shown in Figure 2. R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w ith o u t perm ission. 1n Figure 2: Sites in Zeolites hexagonal rin g Large cavity sodalite unit hexagonal ring from reference 56 R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 15 Interesting chemistry results from these exchangeable cations. presence of These cations are only loose ly bound to the zeolite and are, bile. the therefore, somewhat mo These cations can be replaced by other ions such as rare earth ions to produce samples that luminesce method commonly ion-exchange. ites with used to replace these cations . One is called It routinely involves the stirring of zeol aqueous solutions of Prolonged and 57 the ion to repeated exchanges cation that is replaced. is usually determined, increase the amount of The upper limit of ion-exchange however, by the Si/Al ratio since the number of exchangeable cations of aluminum ions. be exchanged. is equal to the number Variations in the ion-exchange capacity of zeolites can be achieved by the synthesis of new zeol ites which can have more or less cation exchange capacity. 1.3-1 .^ New Zeolites Recently, new classes of zeolites have been prepared. These new zeolites involve substitution of different atoms into the framework of the q r R-62 aluminophosphates' *' or sophates^, aluminosilicate. In this way, ALPO^'s and sil icoaluminop'n- or S A P O ’s, have been formed. These new zeol ites have new and interesting properties and have intro duced some new three dimensional structures to of zeolites. A l P O ^ ’s q 158-62 are the class electronically neutral and therefore have no exchangeable cations. fciO SAPO’s con R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 16 tain exchangeable cations. Iron has also been incorporat ed into the zeolite framework forming what has been called aluminof errisilicates** ^ ^ be used to incorporate ^ . Many different methods can metals into zeolites, ion-exchange and framework substitution. methods will be discussed in including Several of these the next section. Figure 3 shows how some iron ions can enter the zeolite framework. R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 17 Figure 3: Zeolite Framework Replacement \ ' Si o' 0 \ fi Al \ / Si .0' Si / R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 18 1.3*2 Precursors Of Supported Metals Several complexes metals on supports. of metals Carbonyl species were used in several of as one of were employed the studies. of iron and cobalt Ferrocene was used the starting materials in the crowave method method. to prepare Ions of iron reduction by mi were ion-exchanged into zeolites from several starting compounds such as fer ric nitrate and iron nitroprusside. The structures of several of these starting materials will be discussed. Several different carbonyl species were employed. Fe(CO)j-f Fe2 (C0)g and Co2 (C0)g were all utilized as starting materials in our research. The structures are known for the various iron carbonyls that were studied. iron in bridging a trigonal bipyramid with the center and carbonyl three equatorial Figure Fe(CO)^ is positions. Fe2 (C0)g carbonyls and is a groups at two The linear three structure of Fe2 (C0 )g which is structure is axial and shown in structure with three terminal carbonyls. The also known as diiron nona- carbonyl is shown in Figure 5. R eproduced w ith perm ission o f the copyright owner. F urther reproduction prohibited w itho ut perm ission. 19 Figure 4: Structure of Fe(CO)^ 0 c / 0 <T> O u a c ^ F e ^ " ID \ 0 0 4. 5 from reference 128 R eproduced with perm ission o f the copyright owner. F urther reproduction prohibited w itho ut perm ission. 20 Figure 5: Structure of Feo (C0). on lO lO CNJ OsJ lO 3.7 from • C O Fe refe re nc e 129 R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 21 Co2 (CO)g is a linear molecule nal carbonyls similar to with bridging and termi Fe^CCO)^. The structure Co2 (C0)g is shown in Figure 6 . R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. of Figure 6 : Structure of Co_(C0 )o 2 8 co 121 <NJ LO i S- 2 from • Co o C • 0 reference 187 R eproduced w ith perm ission o f the copyright owner. F urther reproduction prohibited w itho ut perm ission. ?3 Ferrocene is a sandwich compound. It is called a sand wich compound because the iron atom is located between two cyclopentadienyl rings like a sandwich. The structure is shown in Figure 7. 2The structure of dron. Fe(CN)cNO b is related to an octahe- This compound is shown in Figure 8 . R eproduced with perm ission o f the copyright owner. F urther reproduction prohibited w itho ut perm ission. ?.n Figure 7: Structure of Ferrocene Fe fNJ CO kl from reference 188 R eproduced w ith perm ission o f the copyright owner. F urther reproduction prohibited w itho ut perm ission. Figure 8: Structure of Nitroprusside Anion 0 a N V* N C' LO 00 LO -'N 4. 33 from reference 189 R eproduced w ith perm ission o f the copyright owner. F urther reproduction prohibited w itho ut perm ission. 25 1.3.3 220.127.116.11 Metal Loaded Zeolites Iron Loaded Zeolites Morice and R e e s ^ studied ion-exchange of several zeolq ites including In many X and Y with cases breakdown of occurred and Fe 2+ solutions of FeJ + the structure of ions oxidized to Fe “ 5+ and Fe p+ the zeolite ions. To avoid this structural breakdown, Collins and Mulay obtained iron loaded Fe(C0)j- and FeCl^ was introduced zeolite. in zeolites. by the FeCl^ was Both samples zeolites Fe(CO)^ is deposited from contained iron and the incorporation spraying of a Mossbauer spectroscopy, ceptibility by a liquid and fine mist an ether oxide and electron microscopy. onto the solution. were analyzed X-ray diffraction, of by magnetic sus Other synthetic methods have been used to avoid breakdown of the structure of the zeolite. f Q - (7A Delgass and coworkers prepared iron loaded zeol ites without structural degradation by the careful adjust ment of the solution pH before ion-exchange. A pH of 3-8 - 4.0, prepared by the addition of of sulfuric acid to the zeolite-water mixture, They studied allowed exchange of the Fe these samples by Mossbauer 2+ ions. spectroscopy and also observed the effect of adsorbates such as ammonia and oxygen. R eproduced with perm ission o f the copyright owner. F urther reproduction prohibited w itho ut perm ission. 27 Garten and Fe P+ coworkers in mordenite. 71 extended this work He studied these samples as catalysts in the reverse of the water gas shift reaction — > H20 + and the ammoxidation of CO) acrylonitrile. to include Studies of Fe p+ (H2 + C02 propylene to form ions in ZSM^5 have also been done. Petrera and coworkers 72 have recently done some Moss bauer studies of large coordination complexes of Fe^+ that were ion-exchanged into ZSM-5. ious exchange sites like cobalt have They investigated the var in this zeolite. also been Other metals ions ion-exchanged into zeolite ZSM^-57 3 . 18.104.22.168 Cobalt Loaded Zeolites Cobalt ions have Stencel and with cobalt. Co P+ ions in coworkers been 73 incorporated into have studied zeolites zeolites 73 . exchanged They observed the formation of nonreducible interior sites sites of ZSM-5 and reducible cobalt oxide on exterior sites of ZSM-5. complexes can also be placed Cobalt and iron in zeolites by the technique of metal atom vaporization. 22.214.171.124 Metal Atom Vaporization Metal atom vaporization rate metals into 74-83 has been used to incorpo zeolites and other supports. Ozin and R eproduced with perm ission o f the copyright owner. F urther reproduction prohibited w itho ut perm ission. ?8 yh gO coworkers have used metal vapors rather than metals. ion-exchange methods, This metal under technique involved high of iron and cobalt, to prepare supported the vaporization of a vacuum and the subsequent trapping and solvating ofsmall particles of this metal which were then dispersed onto a support. resulting in The solvent was then removed the preparation of the supports. small metal Ozin and coworkers some of their preparations. Mossbauer spectroscopy and Tropsch reaction. 7 i i - AO used clusters on zeolites in These samples were studied by as catalysts in the Butenes were selectively reaction of carbon monoxide and Fischer- produced by hydrogen over these cata lysts . Guczi 84 has reviewed several of metals into supports. methods Jacobs of incorporation 85 86 ’ has reviewed the in corporation of several metals into zeolites. zeolites can also be prepared using similar techniques as presented by Guczi 84 and Jacobs 85 by loading Bimetallic two metals into a zeolite. 1 -3-3-^ Bimetallic Zeolites There has been some recent work on mixed metal systems and bimetallic systems, demonstrating the changes in prop erties of a metal when it is influenced by another metOy al . The term bimetallic in our work refers to the pres R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 29 ence of two transition metal ions which can be in ionic or metallic states. the presence This is related to our research since of another metal might lower decrease the sintering that temperature or higher temperature in our samples. the reduction occurs at a This second metal may also change the activation energy of a reaction or influ ence the adsorption or desorption properties of a sample. One article that was particularly relevant was the work of Scherzer and Fort iron and other zeolite Y. 88 . They prepared bimetallic samples of transition metals in the The procedure ammonium form of incorporated the initial ex change of a divalent cation like cobalt or copper followed by the subsequent exchange with an iron anion ii_ ?_ Fe(CN)g and Fe(CN)^NO are two of the anion complexes that were employed. formed a complex in the zeolite form metallic iron. The cations species. and anions which could be reduced to Scherzer and Fort successfully prepared reduced iron 88 89 ’ by this method in zeolites. We have prepared some samples using the method of Scherzer and QQ Q1 Fort ’ . Similar systems can be prepared by loading of metals on other supports. 1 .3•^ Iron And Cobalt On Other Supports Delgass and coworkers 92-95 studied the Mossbauer and Fischer-Tropsch properties of iron and iron alloys on oth er supports such as silica. These systems can be compared R eproduced with perm ission o f the copyright owner. F urther reproduction prohibited w itho ut perm ission. 30 to the iron on zeolite systems. Cobalt has also been loaded onto silica and other supports. Meyers and Hall composition of 96 prepared cobalt on alumina by the de Co^(C0)12 . They studied the Fischer- Tropsch activity of the resulting sample. Bartholomew Co^(C0)12 and coworkers and incorporated well as other supports to talysts. also cobalt nitrate decomposed on silica as form Fischer-Tropsch active ca They prepared catalysts that produced a variety of hydrocarbons. fell in 97 98 ’ the A significant percentage of the product to range. treatment of the cobalt use as a catalyst. Their work involved pre complex (decomposition) There are prior to many other methods of pre treatment or activation of samples. 1.3*5 Methods of Activation Of Supported Metals Activation procedures are an area of synthesis that has been thoroughly studied. There are several types of acti vation procedures including thermal, chemical, photochemi cal and microwave. 1.3*5.1 Thermal Activation Heat is a common activation procedure, since many spec ies decompose at high temperatures or reduce at high temp- R eproduced with perm ission o f the copyright owner. F urther reproduction prohibited w itho ut perm ission. 31 eratures to form active species. the work of Huang and Anderson Huang and Anderson 99 99 One such study involves . studied the Fe^+ on zeolite Y by hydrogen. would reduce to ther. Fe 2+ reduction of Fe 2+ and They found that Fe^+ ions but that Fe 2+ would not reduce fur Metallic iron which was the intended product of the reduction was not produced. Gao and Rees*'l“,<") also had dif ficulty in producing metallic iron. Gao and Rees10^ studied the ite A. son 99 . reduction of Fe^+ in zeol They obtained similar results to Huang and AnderThey could form ferrous ions but Other heat treatments of Fe^+ ions in no iron metal. zeolites have been done. Kulkarni and Kulkarni101 studied of Fe^+ in zeolite Y. the thermal stability They found that the ferric ions mi grated from the supercages to the sodalite cages or hexag onal prisms at 500°C. This migration was analysis of differential thermal diffraction showed framework for lattice high loadings determined by analysis data. distortion of ferric of ions. the X-ray zeolite This was shown by a decrease in the relative intensities of certain hkl planes. lysts. Many heat activated samples are used as cata- One example is the work of Petunchi and Hall 1 02 R eproduced with perm ission o f the copyright owner. F urther reproduction prohibited w itho ut perm ission. 32 Petunchi and Hall102 prepared Fe2+ mordenite using on zeolites Y and Q and coworkers the procedure of Delgass and studied the resulting catalytic properties for the ox idation of CO with NO, Op and ^ 0 . tivity and They compared the ac susceptibility to poisoning of the two zeol ites . Lo and coworkers1^ ’1®^ heat treated Fe^+ ions drogen to prepare Fischer-Tropsch catalysts. in hy These Fe^+ ions were impregnated into ZSM-5 and silicalite. Silical- ite is a zeolite that is isostructural with ZSM-5 but the11 oretically has no framework aluminum . Impregnation in volves the contact support. of a solution of metal ion with a Usually only enough liquid as necessary to dis solve the metal ion precursor compound is employed. The solution is then evaporated off leaving the metal compound on the support. This is different than ion-exchange where only the metal ion is incorporated into the support. impregnation, the entire metal Lo and coworkers 10S 10^4 compound is incorporated. then studied the catalytic activi ty of these samples for Fischer-Tropsch synthesis. discussion 1.3.6. of Fischer-Tropsch Mossbauer spectra were Fischer-Tropsch reaction. the methane to butane involve heat treatment derson^, With Synthesis, section obtained before and after Most of the products range. were in Most activation procedures such as the work of Gao and Rees11^ , see For a Huang and An Kulkarni and Kulkarni1^1 , R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. Pe- 33 tunchi and Hall 102 other activation and Lo and coworkers procedures like chemical 103 1 although activation can have certain advantages. 126.96.36.199 Chemical Activation Gunsser and coworkers1 and Lee10^ used a chemical ac tivation of iron zeolites. metal vapor as They studied the use of sodium a reducing agent. transfer electrons to the iron and Na+ in the zeolite. tion occurred. Sodium metal could ions to form metallic iron Unfortunately, incomplete reduc Complete reduction of iron has been achieved with the use of photochemical activation. 188.8.131.52 Photochemical Activation Derouane and coworkers 14 used photochemical activation step to bonyl on zeolites ultraviolet light as a decompose iron pentacar- to form metallic iron. They reported the production of highly dispersed, pyrophoric iron parti cles. Ultraviolet light has also been used in photocataihO lytic studies of Fe(C0)^/zeolites . Suib jet.al. stud ied the conversion of 1-pentene to cis and trans 2 -pentene on these catalysts 10 8 . Photochemical the use of heat in pretreatment. activation avoids Another activation tech nique that does not require heat is microwave activation. R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 34 1.3*5.4 Microwave Activation Microwaves ecules have been to form agents1^ ’11 0 . used to are good mol hydrogen atoms which This method of activation avoids the use of heat and has been reducing successful in preparing small parti cles of nickel on zeolite the use of activate hydrogen Y. This work has demonstrated ferromagnetic resonance to study the magnetic properties of the samples and to get an approximate parti cle size of the metal. Other reports of the use of ferro- magnetic resonance in similar systems can be found Another report of the use of microwaves production of then be used volved the a highly energetic 121 involves the argon plasma to decompose metal halides. preparation of electrodeless . which can This work in discharge lamps. The system was a closed unit containing Mnl2 , silica chips and a reduced pressure of done a lot of work book which reviews argon gas. with plasmas McTaggart1 and has written the area of chemical has a good reactions in the plasma. Microwaves have also been used to 1 2 ^ ip J i such as zeolites (RF) dehydrate supports 1 2 R . Bartley used radio frequency waves to modify the catalytic properties of a sample of iron on SiO^-Al^O^. rectly by the The iron particles were heated di RF waves and the by conduction from the iron. silica-alumina was heated These catalysts were used in R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 35 the hydrogenation cyclopropane. activated, of propylene and the As with Bartley’s work they are often used 1 25 isomerization of , once samples are as catalysts in reactions such as Fischer-Tropsch synthesis. 1.3*6 Fischer-Tropsch Synthesis Fischer-Tropsch synthesis is one of the reactions that 1 2 f\ is catalyzed by iron and cobalt 1 O *7 * . This synthesis involves the production of hydrocarbons from carbon monox ide and hydrogen in the following reaction: nCO + (iJn+2)H2 H ( C H 2 )n H Catalytic studies of metal containing zeolites recent past have focused ity. + nH2 0 in the on efforts to increase selectiv Selectivity is the ability of a catalyst to form one product. Jacobs has addressed this area directly 109k . He suggests that metal zeolites are important Fischer-Tropsch catalysts and describes how they will effect the future of this area 128 . schemes impose Deviations from He states, "Schulz-Flory polymerization severe limitations upon Schulz-Flory kinetics by tions on dual-component catalysts this selectivity. secondary reac (classical CO reduction function mixed with a shape selective acidic zeolite) prove range." the selectivity mainly in the gasoline im number Schulz-Flory polymerization is the mechanism that is accepted as the pathway for the formation of hydrocar- R eproduced w ith perm ission o f the copyright owner. F urther reproduction prohibited w itho ut perm ission. 36 bons in the Fischer-Tropsch reaction. its the products that can lie in the This mechanism lim be formed. Desirable products gasoline range since this is one of the reac tions studied for the production of synthetic fuels. 1->o way to change this selectivity, Jacobs suggests , use a dual component catalyst, on a zeolite. One is to such as a metal supported The metal would provide the active site and the zeolite would introduce shape selectivity1^3-1^8 . a discussion on shape selectivity, see section 1 .3 .5 .1 . i pQ He also states , "The encagement of these particles in a stable manner in zeolite cages seems the most likely route to prepare selective FT catalysts." that the metal be _in the zeolite cages. It is important The metal parti cles must be small enough to fit into these cages (11 Ang stroms in zeolites X and tempted to prepare Y). Several workers small metal particles on have at the order of zeolite cages. Jacobs also occurs no was used. commented 129 matter what the that in all cases sintering reducing agent or This results in the external surface of the zeolite. which metal formation of metal on the This sintering could be drastically reduced with the use of low reduction temperatures 129 Jacobs proposes 129 in the preparation of that heat is a very important factor these samples. Overheating causes R eproduced w ith perm ission o f the copyright owner. F urther reproduction prohibited w ith o u t perm ission. 37 the metal and to sinter and underheating does Phillips and carbonyls Dumesic for the since their migrate to the not completely 130 reduce the have suggested production of the use small metal reduction temperature is for metal salts. external surface so much metal. of metal particles lower than They suggests that supported metal sys tems could eventually approach the atomic dispersion limit with these samples. Changes in the catalyst can have some effect on the mechanism of the reaction. anism are therefore Studies of mech very important in the study of cata lysts. Mechanisms of the Fischer-Tropsch 131-138 suggested 3 0 . reaction have Niemantsverdriet and coworkers gested that surface carbides are active catalysts. The formation of these 1 33 been sug Fischer-Tropsch active carbides is an initial activating step. Mossbauer studies have been reported of iron car- 1 • 3 Q - 1 2J2 bides . These and bulk carbides. studies have involved The method of growth of the hydrocar bons has been studied. Some authors favor a mechanism in volving polymerization of surface prefer the insertion are factors CH^ groups while others of CO into a surface hydrogenation of the CO. nometallic aspects both surface 1 37 Herrmann J of Fischer-Tropsch that influence the chain and then discussed the orgasynthesis. mechanism of There a reaction. R eproduced w ith perm ission o f the copyright owner. F urther reproduction prohibited w itho ut perm ission. 33 Some of these factors are shape selectivity and catalyst acidity. 184.108.40.206 Shape Selectivity Shape selectivity 1ln-i 48 J is an effect that as zeolites can have on a reaction. shape selectivity due cages and pores. lectivity. to their There are supports such Zeolites can exhibit framework structure of different types of shape se Reactant selectivity occurs when reactants that are small enough enter a pore and react whereas large reactants are excluded 144 . Product selectivity occurs when the size of the product is determined by the pore Metals supported on zeolites tivity in 144 can introduce product selec reactions such as the Fischer-Tropsch reaction and gasoline range hydrocarbons could possibly be prepared using a zeolite with the correct pore size. One example of shape selectivity is the Mobil methanol to gasoline 14Q IRQ synthesis ’ . ZSM-5 has been shown to catalyze the formation of This is a gasoline range hydrocarbons from possible route for the methanol. production of synthetic fuels. 220.127.116.11 Catalyst Acidity The acid nature of catalysts studied in great detail 151-158 Bronsted and Lewis acid sites. such as zeolites has been . Zeolites contain both Bronsted sites are present R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 39 in the form of Lewis sites groups. OH groups are present The in the aluminum ion in electron pair acceptor. acid sites attached to form of A1 and Si atoms. A10^ + and these oxide species A10+ is an The strength and number of these varies over the different types making them good cracking catalysts 151 . of zeolites, This is important because cracking reactions form small useable hydrocarbons from large chain hydrocarbons. of reactions often involves to characterize important to The study of these types many spectroscopic techniques the catalysts. The techniques the research discussed in that are this dissertation will be presented in the next section. 1.4 INSTRUMENTAL TECHNIQUES WHICH ARE USEFUL FOR STUDYING THESE ZEOLITE SYSTEMS The study of catalysts such can involve many characterization tronic, structural and chemical as metal loaded zeolites techniques. The elec properties of a catalyst can be determined by these techniques. 1.4.1 18.104.22.168 Methods For Probing Electronic Properties Mossbauer Spectroscopy Mossbauer spectroscopy is an important technique in the study of oxidation many reports states of elements. of Mossbauer There studies have been of zeol- R eproduced w ith perm ission o f the copyright owner. F urther reproduction prohibited w itho ut perm ission. 40 .. 66-72,74-80,89,99,100,105,106 ites ’ ’ * . been thoroughly studied by Mossbauer Mossbauer data for Fe(C0)^ Fe(CO),. is Fe2(C0)g has also been have spectroscopy. The have been reported^**. bauer studies of Fe(C0)^ are tures because T . Iron carbonyls Moss usually done at low tempera a liquid at room temperature. studied by MSssbauer spectroscopy, but since it is a solid, it can be studied at room temperature 154 ety of . ligands to studies ed Fe(CO)^ will exchange one CO group for a vari 154 -160 of . form a FeCCO^L Fe(C0)1}L species. type species have Mossbauer been report- The Mossbauer analysis of ferrocene and ferro- cene derivatives has been done 161 . Table 3 contains the Mossbauer data for the iron carbonyls and ferrocene. R eproduced w ith perm ission o f the copyright owner. F urther reproduction prohibited w itho ut perm ission. TABLE 3 Mossbauer Data For Iron Compounds Compound Fe(C0)R a Fe? (C07q FeTC5H5 52 IS (mm/sec) 0.09 0.28 0.07 QS (mm/sec) 2.57 0.54 0.24 a - taken at -195 C carbonyl values from reference 100 ferrocene value from reference 92 R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 42 A diagram of the basis of in Figure 9. a Mossbauer experiment is shown A radioactive, gamma ray emitting source is positioned next to the sample. Atomic nuclei in the sam ple are excited by the absorption of gamma rays of appro priate energies (energies equal to the transition energy). The gamma rays that are emitted by the source are of a fixed energy and vibration of the source can vary this en ergy. In this way, gamma rays of the energy of the tran sitions are generated. All gamma rays other than the ab sorbed rays are transmitted to the detector. of these transitions is determined ple such as oxidation state. peaks and their position on an mitted rays can indicate the in the sample. The energy by factors in the sam The number of absorption energy graph of the trans oxidation state of the metal This information can be obtained from the Mossbauer spectrum. R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 43 Figure 9: source Mossbauer Experiment I I naw J m o tio n s a m p le counter no a b sorp tion ▲ count rate m axim um ab sorption ♦ 0 source velocity R eproduced w ith perm ission o f the copyright owner. F urther reproduction prohibited w itho ut perm ission. 44 Several bits of information can Mossbauer spectrum. value. obtained from a All data is referenced to a standard This is usually the center pattern of be alpha iron point of the six line which is given mm/sec (velocity of the source). the value of zero One must be careful when comparing literature data because different references are often used. The shift of a peak or the center of split peaks is given the name 'isomer shift'. tween peaks is called isomer shift tion the 'quadrupole can be calculated splitting'. from the The following equa- 162 IS = cs1 + s2 + s3 + where sec. The distance be s4 ) A are the positions of the peaks in mm/ This is for a sample with four Mossbauer peaks. equation can be changed so that the number of The S terms is equal to the number of peaks in the spectrum if there are less than quadrupole splitting four peaks. The calculated from the following equation 162 can be : QS = (S1 + S6 - S2 - S5 )/4 This is also for a sample with four peaks. er peaks, the equation is modified. nals are present When Mossbauer sig for more than one type the isomer shift and quadrupole Again for few of iron nucleus, splitting values are cal- R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 45 culated separately. For an indepth discussion bauer spectroscopy, ’the reader 162 through Another technique that 168. tronic information on a of Moss is directed to references catalyst is provides elec ferromagnetic reso nance. 22.214.171.124 Ferromagnetic Resonance Ferromagnetic resonance 169 netic properties of samples mentally, involves a study of the mag versus temperature. the technique is identical to electron paramag netic resonance. A sample and the absorption to calculate a is irradiated with microwaves of these waves is plotted tain range (in Gauss). The position "g" value. For powder called a g-apparent value since ticles Instru- is fairly aligned as in a random. If over a cer of the peak is used samples, this is the alignment of the par the particles could crystal then a g-parallel value perpendicular value could possibly be measured. values were anisotropic in all crystallographic be and a gIf the g direc tions, a g , g and g value could be measured, x y z The calculation of the g value lowing equation 170 was done using the fol- : g = hV/BH R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 46 where h = Planck's constant, B = the Bohr magneton, V = the microwave frequency, H = the magnetic field. romagnetic materials, the g-apparent value and the linew- idth change with temperature, of the broadness of The linewidth is a measure a peak and maximum to peak minimum. is calculated important. The from peak Above a certain temperature, the g-apparent value becomes constant as netic species. For fer in a simple paramag temperature at which this occurs is The exact value of this temperature depends on the particle size of the ferromagnetic species. An esti mate of the particle size can be obtained from experiments of this kind 109 Electron paramagnetic resonance (EPR) and ferromagnetic resonance (FMR) iron and sample are important techniques for the study of cobalt samples. are determined by The magnetic properties the electronic of a configuration. Table 4 lists the electronic configurations for the common states of iron and cobalt. Ferric ions are EPR active but high spin ferrous ions are hard to orbit coupling. Co 2+ ions are see by EPR due to spin easier to see than Co ions especially in the low spin configuration. R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 2+ TABLE 4 Electronic Configurations of Iron and Cobalt substance electronic configuration ,6 Fe CO CO3* Hs*3d 6 4s°3d 5 fa'hi7 Hs‘3d 4s°3d 4s 3d R eproduced w ith perm ission o f the copyright owner. F urther reproduction prohibited w itho ut perm ission. 48 Electron paramagnetic resonance has been high spin Fe^+ ions i n •zeolites171~ 1 . used to study Another technique that is useful in probing the electronic properties of ca talysts and complexes is infrared spectroscopy. 126.96.36.199 Infrared Spectroscopy Infrared spectroscopy can be used to observe the pres ence of infrared active groups such as CO, OH, etc. tions and intensities tion about the of these signals can sample environment Several reviews have dealt with ganic systems 175 . concentration. infrared studies of inor- been done on Fe(CO)^ Ferrocene contains that are infrared active been done. give informa 47 175 ’ . Infrared studies have Fe2 (C0)g and Posi 175 . as well as cyclopentadienyl groups Studies of this compound has Infrared spectroscopy of Co2 (C0)g has been 1 7CZ done . The infrared properties of a sample dependent on its structure. For this reason, are often it is impor tant to study the structural properties of a system. 1.4.2 188.8.131.52 Methods For Probing Structural Properties Electron Microscopy Electron microscopy allows an experimenter the surface morphology (texture, size of a sample. structure) to observe and particle X-ray analyzers coupled to an electron R eproduced w ith perm ission o f the copyright owner. F urther reproduction prohibited w itho ut perm ission. 49 microscope enable elements. one to get a surface Electron microscopy surface structural properties. concentration of gives information about Bulk structural properties can be obtained from X-ray powder diffraction. 184.108.40.206 X-ray Powder Diffraction X-ray powder tures diffraction can be because solids pattern. give Changes in this used to study struc a characteristic diffraction diffraction pattern can denote structure change or structural breakdown. Metals can also give diffraction patterns if incorporated into a solid in a significant amount. 1.4.3 Methods For Probing Chemical Properties 220.127.116.11 Gas Chromatography Gas chromatography q u e ^ ^ ’1^^. Gaseous is an important separation techni- and volatile liquid samples analyzed by this method. can be Concentrations of gas components can be obtained for the analysis of a reaction system. 1.4.3-2 Gravimetric Techniques Thermal gravimetric analysis and analysis are two important techniques materials. When samples are heated, differential thermal in the study of new the weight often de creases due to the loss of some material. Frequently, wa R eproduced with perm ission o f the copyright owner. F urther reproduction prohibited w itho ut perm ission. 50 ter is given off while at poses. This point at other times, usually happens at high which this weight loss the sample decom temperature. occurs is The significant. Gravimetric techniques give a great deal of information in this area. 1.5 RATIONALE 1.5.1 Catalyst Synthesis Various synthetic methods were small metal particles in zeolites. to study the effect of Fischer-Tropsch activity the of employed prepare Zeolites were employed various pore the to sizes on resulting the catalysts. Shape selectivity of the zeolites on the reaction products was investigated. to avoid Microwave discharge the introduction of heat into methods were used the preparation. Heat can sinter particles and force them to migrate to the external surface of a support. vide the sintering. Microwave discharges pro energy for catalyst preparation without causing Sodium vapor treatment and hydrogen treatment were employed at low temperatures to achieve reduction but avoid sintering. The effects of these preparations were studied with catalytic reactions. R eproduced w ith perm ission o f the copyright owner. F urther reproduction prohibited w itho ut perm ission. 51 1.5.2 Catalytic Reactions Fischer-Tropsch reactions were used lytic properties of to study the cata the iron and cobalt catalysts. The Transient Pulse Method was employed to study surface spec ies on the catalyst and tion times. A flow reactor line was employed to study the concentrations of times. The reactions products at short reac hydrocarbons produced at activity of a catalyst can be short and long reaction times. become inactive with time. long reaction different at Initially active sites may These initial sites may effect the formation of other sites and effect the catalyst life. Studies of short and long reaction times can give informa tion about the changes that reaction. The activity electronic, talyst. a catalyst undergoes during a of the catalysts depends on the structural and chemical properties of the ca Various spectroscopic techniques were used to study these properties. 1.5.3 Spectroscopic Characterization One novel feature of in-situ Mossbauer reactor. before, this research is Mossbauer the use of an analyses were done during and after Fischer-Tropsch reaction without any contamination from atmospheric water or oxygen. bauer spectroscopy and ferromagnetic resonance Moss were used to determine the oxidation states of the metals on the ca R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 52 talysts. Ferromagnetic resonance and electron microscopy were used to measure the particle size of the metals. frared spectroscopy was used to CO or other In analyze for any remaining ligand groups on the metals after reduction. We have tried to use a variety of spectroscopic techniques to support the results and to give as much information as possible about our catalysts. We recognize the problems with basing conclusions on information from one technique. 1.6 FOCUS We have tried to build on have used the research of others. compounds that others carbonyls, have used such organometallic compounds and are ion-exchanged into zeolite samples. We as metal metal ions which We have also used reported techniques like reduction by hydrogen, sodium va por reduction novelty of and microwave treatments. this research, however, lies in the use of low reduction temperatures to minimize sintering, bonyl species (which decompose at the use of microwaves technique. The as a the use of metal car a low temperature) room temperature and activation Different metal precursors and various reduc tion techniques were studied. R eproduced with perm ission o f the copyright owner. F urther reproduction prohibited w itho ut perm ission. Chapter II EXPERIMENTAL METHODS 2.1 INTRODUCTION This chapter is included to explain the instruments and experimental procedures that were used. planations of the More detailed ex various techniques can be references given in each section. found in the The importance of each of these techniques has been given in the introduction. 2.2 MOSSBAUER SPECTROSCOPY All Mossbauer spectra were recorded in the transmission mode. The instrument incorporated an Elscint Mossbauer drive unit, an Elscint function generator model MFG 3A, an MVT-3 linear velocity transducer driving unit. preformed by and an MD-3 transducer Detection of the transmitted gamma rays was a Reuter-Stokes Kv-CH4 proportional counter powered by an Ortec *401 A/456 high voltage power supply and coupled to an Ortec 142 PC preamplifier. Signals were transmitted from the preamp through an Ortec 571 spectros copy amplifier to a Tracor Northern analyzer for storage. NS-701A multichannel Plots of the data were later gener ated on an IBM 360/370 computer. - 53 - R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. The Mossbauer system employed an in-situ treatment cell similar to that of Delgass hydrogen, 1 7 fi . It allowed treatment with hydrogen/carbon monoxide mixtures or oxygen and Mossbauer analysis without any exposure to the atmosphere. A drawing of this cell is shown in Figure 10. R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 55 Figure 10: In-situ Mossbauer Cell He H2 vent ■ 0 1 co+h 2 0 - o X R eproduced with perm ission o f the copyright owner. F urther reproduction prohibited w itho ut perm ission. 56 2.3 ELECTRON PARAMAGNETIC RESONANCE/FERROMAGNETIC RESONANCE Paramagnetic and ferromagnetic samples with a Varian E-3 spectrometer. at an X-band frequency 250°C using of approximately a temperature heated or cooled nitrogen. tubes under vacuum. studied The samples were analyzed temperature of the samples could to were 9.5 GHz. The be varied between -160°C controller and a flow of Samples were sealed in quartz The instrument was calibrated with cobalt(II) in MgO. 2.4 ELECTRON MICROSCOPY Particle size were preformed analysis and surface using scanning electron transmission electron microscopy. tron microscope was a Hitachi supported on copper 300 mesh carbon. methanol. mixture prior to on the grids while dis mixture. done on an AMR Studies of surface Samples were grids which were coated with of the contact with the grid aided croscopy studies were and The transmission elec Ultrasonification duction of a homogeneous ment. microscopy model HU200. The samples were placed persed in morphology studies methanol in the pro Scanning electron mi model 1000A instru concentrations were done using Energy Dispersive X^-ray Analysis with an EDAX 9100/60 sys tem. The accelerating voltage employed was 20 keV. R eproduced with perm ission o f the copyright owner. F urther reproduction prohibited w itho ut perm ission. 57 2.5 X-RAY POWDER DIFFRACTION Samples were studied for bulk ray powder diffraction. These DIANO-XRD 8000 diffractometer. copper K-alpha. structural changes by Xstudies were The done on a source radiation was Diffraction patterns were usually run be tween 10 and 80 degrees two theta. 2.6 INFRARED SPECTROSCOPY Infrared spectra were recorded on 283 spectrometer. a Perkin Elmer model Powder samples were dispersed in miner al oil and placed between two KBr discs. 2.7 GAS CHROMATOGRAPHY Reaction products were analyzed 5880A gas chromatograph. The carrier helium at a flow rate of 25 mL/min. ture was 200°C and the detector Thermal conductivity was umns. Molecular sieve Hewlett Packard gas was zero grade The injector tempera temperature was employed using two sets 13X columns were used temperature of 35°C to separate ide. on a 210°C. of col at an oven methane and carbon monox Alltech VZ-10 columns were used at 50°C to separate ethane, ethylene and higher hydrocarbons. These separa tions were compared to standards of natural gas, ethylene, propane, multiplied propylene by weight and butane. factors to The product obtain weight areas were percent. R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. The values of the weight percents Product samples were introduced by are given in syringing out Table of in-line septa. R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 59 TABLE 5 Weight Percent Values Compound methane ethane ethylene propane propylene butane isobutylene 1-butene trans-2-butene cis-2‘-butene nitrogen oxygen carbon monoxide Weight Factor 0.45 0.59 0.585 0.68 0.652 0.68 0.683 0.697 0.658 0.643 0.67 0.80 0.67 taken from McNair and B o n e l l i ^ ^ R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 60 2.8 THERMAL ANALYSIS TECHNIQUES Analysis of the aluminoferrisilicates of a Perkin-Elmer System 7 A Model 1700. involved the use Differential Thermal Analyzer Samples were heated from 50°C to 750°C in ar gon at a heating rate of 20°C/min. mL/min and all samples were The argon flow was 11 referenced to alumina. Sam ples were loaded into alumina crucibles for analysis. 2.9 MICROWAVE GENERATOR The microwave generator used in the discharge experi ments was marketed by Raytheon model PGM-10. microwaves of frequency 2*150125 MHz. It generates Microwave power was measured by a Micro Match standing wave ratio bridge. The cavity employed was an Evenson quarter wave, coaxial cavi ty incorporating both tuning and coupling adjustments. All sample tubes were made of quartz. 2.10 REAGENTS A variety of zeolites were employed in the experiments. Zeolites NaA, NaX, NaY and ALFA Co. in powder form. NH^Y were purchased from the The lot numbers were as follows: NaA(4A) - 061 576; NaX(1 3X) - 072182; NH^Y(SK-41) - 042578. NaY(SK-40) - 042578; NaZSM-5 was prepared according to the patent of Argauer and Landolt 1 71 example 27 which sug gests the combination of colloidal silica, tetrapropylam- R eproduced with perm ission o f the copyright owner. Further reproduction prohibited w ith o u t perm ission. 61 monium bromide, an autoclave sodium aluminate at 175°C for and sodium hydroxide in 8 days. HZSM-5 was prepared from NaZSM-5 by exchange with dilute acid. nite was obtained from Strem Chemicals, Sodium morde- Inc. and its lot number was 10282-52. Bentonite and titanium dioxide were obtained from Fischer Scientific with their lot numbers being 730635 and 725845 respectively. Alpha alumina and amorphous silica were purchased from the Illinois Minerals Co. Iron pentacarbonyl was received from the ALFA Co. lot number was 091179. Sodium nitroprusside, Its The iron carbonyl was 99.5% pure. Na2Fe(CN),-N0, and ferrous sulfate, FeS0jj*7H20, were purchased from the J. T. Co. with lot numbers of 52848 and 41898. Baker Chemical Copper nitrate, Cu(N0^)2*6H2 0, and cobalt nitrate, CoCNO^)2*6H20, were manufactured by the General Chemical Division of Allied Chemical and Dye Corporation with their respective lot numbers being W030 and H018. ZnCNO^^* 6H2 0, Zinc nitrate, was purchased from Fischer Scientific with a lot number of 791947. Iron nitrate, FeCNO^)^ *9H20, was purchased from ALFA products, lot number 06031. Aluminum nitrate, AlCNO^)2 ’9H20, was from Mallinckrodt Chemical Works, lot number 3172. solution was a 25% by The tetrapropylammonium hydroxide weight solution obtained from ESA R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 62 corporation - Organic Products Division of 2-1728-0581-11. was also from 1788-0482-06. with a lot number The tetrapropylammonium bromide powder RSA corporation with a lot tion. The It Si02 . The from E. K. 1,6 sodium silicate used was 1.40 g/mL and sodium hydroxide used for pH Industries. It contained Dupont #9 solu had a density of hexanediamine was 5932. of The Ludox used in the aluminoferrisilicate syntheses was Dupont HS-30 colloidal silica. 30$ SiO^. number contained 29$ adjustment was The lot number was 014873. from Kodak with a This amine was a solid lot number that melts at dium chloride used was from J. T. The 41°C. of The so Baker Chemical Company lot number 23264. All water used in these experiments was first distilled and then deionized. 2.11 2.11.1 SAMPLE PREPARATION METHODS Iron Carbonyl Zeolites Fe(C0)j- was sublimed at room temperature onto hydrated and dehydrated supports on a vacuum line. sublimed onto a zeolite support The Fe(CO),. was in an inverted "U” tube like the one in Figure 11. In one side of the U tube placed and immediately frozen 0.13 mL of Fe(CO)^ were with liquid nitrogen. One gram of zeolite was placed on the other side of the U R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 63 tube. The tube was fitted with a stopcock and placed on a vacuum line. The system was the Fe(C0)j- frozen. evacuated to 10 -5 torr with The stopcock was then closed and the iron carbonyl was allowed to slowly sublime onto the zeol ite. The sublimation was complete after five minutes. The product had a variety of colors ranging from yellow to orange brown depending on the volume of Fe(CO),. used in the preparation. R eproduced w ith perm ission o f the copyright owner. F urther reproduction prohibited w itho ut perm ission. 6H Figure 11: Inverted U Tube to v a c u u m 1 X —' zeolite Fe(CO) R eproduced w ith perm ission o f the copyright owner. F urther reproduction prohibited w ith o u t perm ission. 65 Fe2 (CO)g Seel 177 Jolly . 178 was prepared according to the report of Fe(C^H^)2 was prepared according to . It was sublimed three times prior to use. After preparation, the Fe(CO)^ sample was with liquid nitrogen. All samples were stored under ni trogen or in a nitrogen filled Fe2 (C0)g was heated glove box until use. to 35°C by a bath to promote sublimation. kept cool hot air gun or The a water Fe(C0)_ and ferrocene sub- limed at room temperature under vacuum so that no heating was needed. 2.11.2 The Hydrogen Reductions samples were press using Typically, pelletized using pressures in the range 176 usually taken at this time. to the reduction temperature, . 16 mm of 3000 to 300 mg of sample were used. placed in the Mossbauer cell a diameter ^1000 PSI. The pellets were A Mossbauer spectrum was The sample was then heated up 300 to 500°C, the procedure, in flowing helium, 100 mL/min. depending on The sample was then exposed to flowing hydrogen, 75 mL/min, for up to hours. The sample was then cooled to room temperature in flowing helium and another Mossbauer spectrum was tak en. R eproduced w ith perm ission o f the copyright owner. F urther reproduction prohibited w itho ut perm ission. 66 2.11.3 Sodium Vapor Reductions Several experiments to reduce iron was in zeolites as reported exchanged into zeolite with 100 trogen. were attempted using zeolites by -5 mixing one studied were A, These samples were filtered, line to 10 by L e e ^ ^ . mLs of 1055 solutions of The zeolites torr. sodium vapor Fe^ + gram of the FeSO^ under ni Y, X and ZSM-5. washed and dried on a vacuum The samples were then placed in the tube shown in Figure 12 with several chunks of sodium that had been washed in hexane. um line and evacuated. heated to 350°C. by turning The tube was placed on a vacu While evacuating, tube was The sodium was then added to the zeolite the dumping tube. collected on the sides of the placed in the a nitrogen The sodium tube. filled glove vaporized and The sample was then box and loaded in a Mossbauer analysis tube. Reduction with potassium vapor was also studied due to the fact that potassium vaporizes at a than sodium. The lower temperature same procedure was followed sodium reduction experiments. as in the Table 6 contains data com paring the vaporization temperatures of sodium and potas sium at various temperatures. R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 67 Figure 12: Sodium Vapor Reduction Apparatus to f va cu u m FeY furnace R eproduced w ith perm ission o f the copyright owner. F urther reproduction prohibited w itho ut perm ission. 68 TABLE 6 Vaporization Temperatures of Na and K Metal Na K Pressure(atm) 1 8^3 10^2. 1128 774 333 jjjzi 231 157 10— 121 62 taken from CRC Handbook"' ^ R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 69 2.11.4 Bimetallic Zeolite Preparations Iron was ion-exchanged into zeolites along metals to prepare bimetallic samples. and ZSM-5, trate, were stirred with copper nitrate, one hour. Typically, solution were used. tered, The zeolites, NH^Y 105# solutions of cobalt ni zinc nitrate and iron sulfate for one gram of zeolite and 100 mL of After exchange, washed with water and dried. stirred with 100 mL of with other the powder was fil The powder was then 105& solutions of sodium nitroprus- side, ammonium ferrocyanide, potassium ferrocyanide or po tassium ferricyanide. washed with water and The resultant powder was filtered, dried on a vacuum line to 1X10 torr. 2.11.5 New Aluminoferrisilicate Zeolite Preparations The author spent two and a half months tional Laboratory working with Dr. synthesis of ZSM-5, with iron substituted silicalite at Argonne Na Lennox E. and ZSM-5 into the framework. Iton on the type zeolites The work fo cused on some work reported in the patent literature10’'1'1. The zeolites that were prepared powder diffraction, differential thermal analysis, tron paramagnetic resonance, bauer spectroscopy. were analyzed by X-ray elec electron microscopy and Moss The samples and their synthesis con ditions are given in Table 7. The amount of iron in these R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 70 samples ranged from 2.62 X 10 ^ moles. The samples moles up to 10.395 X 10 ^ with the lower amounts fairly white in color. to light brown in color. The of iron were higher iron samples were tan The reactant concentrations are given in Table 8. The samples were prepared Tropsch catalysts. to be studied as Fischer- The work was still going on at Argonne at the time of this dissertation. R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 71 TABLE 7 Synthesis Conditions mple # 38 39 40 41 42 43 44 45 46 47 48 type 1 2 2 1 1 2 1 2 1 1 1 Si/Al T emp(— C) Time 140 115 129 11 8 117 129 1 21 150 200 200 175 150 200 150 200 175 175 150 6.8 4.9 3.9 4.9 6.9 6.7 6.7 6.9 6.9 6.7 6.8 type 1 - reference 71 type 2 - reference 72 time - length of synthesis in days R eproduced with perm ission o f the copyright owner. F urther reproduction prohibited w ith o u t perm ission. 72 TABLE 8 Reactant Concentrations Sample # 38 39 40 41 42 43 44 45 46 47 48 mmols Fe mmol A1 Template 3.^335 2.5622 2.5589 3.427 10.375 0.2587 6.6174 0.0262 6.6088 10.395 10.379 1.1258 NA NA 1 .355 1 .233 NA 1 .350 NA 1 .354 1 .232 1 .317 HMDA TPA-Br TPA-OH TPA-OH+Br HMDA TPA-OH TPA-OH+Br TPA+OH TPA-OH+Br TPA-OH+Br HMDA HMDA - hexamethylene diamine NA - none added TPA-OH - tetrapropylammonium hydroxide TPA-Br - tetrapropylammonium bromide TPA-OH+Br - a mixture of TPA-OH and TPA-Br R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 73 2.11.6 Microwave Discharge Preparations The details The microwave of this procedure have discharge experiments dehydrated supports (heated 10‘5 torr), been reported 1 ft n involved the use of to 375°C under vacuum of 1 X vacuum lines and a nitrogen filled glove box. These procedures were followed to exclude water and oxygen from the samples to avoid oxidation of the metals. The metal complex and the placed in opposite sides of in Figure 13. box. dehydrated support were the quartz reactor tube shown This was done in the nitrogen filled glove The complex was placed in position B and the support in position C. Tubes with stopcocks were connected to ei ther end of this tube stopcocks were closed, with CAJON ULTRA-TORR unions. isolating the sample. could then be removed from The The tube the glove box without exposing the sample to air. R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 71} Figure 13: Sample Tube quartz -7 metai B support C R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 75 The quartz tube was then connected shown in Figure 14 and the system to a vacuum line as was evacuated. cocks G and A were closed while D remained open. al complex was then allowed to sublime The sublimation was white zeolite. Stop The met onto the support. evident with a colored complex and a The support particles closest to the com plex first became colored followed by the rest of the sup port. The sublimation time depended on the volatility of the metal complex. ter one half hour. A typical sublimation was complete af At long sublimation times, ports became dark in color and plex were seen crystals of the metal com in the liquid nitrogen sublimation times, less the sup trap. metal was deposited on At shorter the sup port. R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 76 Figure 14: Microwave Line in cr> in c u o u CL z: O o > V) -5 < LU Cd o LU 8 = 0 = ! o o E 3 in o I o ' lu Cl CL l LU m Ll1< cro CL R eproduced w ith perm ission o f the copyright owner. F urther reproduction prohibited w itho ut perm ission. 77 The sublimation was then halted, a liquid ordinarily by placing nitrogen trap at position evacuated. B and the system was Stopcock A was then opened and inert gas from a gas cylinder was allowed to pass over the sample. and helium ments. have been successfully used in Argon these experi A flow controller was adjusted to achieve a pres sure of approximately 0.3 torr of inert gas in the system. This produced a- flow of over the sample. placed around approximately 1.3 mL/min of gas An air cooled microwave cavity was then the tube generator was turned on. at position C and the microwave An inert gas plasma was then ig nited using a Zerostat electric discharge gun. The plasma was highly colored. Carbonyl complexes pro duced a blue plasma due to the emission of CO. rocene present the plasma was initially a In all cases after a few minutes, This is typical for an sample sometimes changed ple) purple color. the plasma turned pink. argon plasma. Agitation the color back to indicating that the penetration is not very far into the With fer of the blue (or pur of the argon plasma solid and that decomposition was not yet complete. The decomposition was assumed to be complete more blue (or purple) color could be generated. was then halted and the system was evacuated. and D were closed and the sample was placed when no The flow Stopcocks A in the glove box until further study. R eproduced with perm ission o f the copyright owner. F urther reproduction prohibited w itho ut perm ission. 78 2.11.7 Microwave Generation of Color Centers During the microwave discharge ites sometimes became experiments, colored faint pink or even at low microwave powers. the zeol faint purple Similar color changes have been reported before for other types of treatments**^** ” ”*®3. Several experiments were attempted color centers existed. (in a few minutes) to prove that these These colors faded so that very quickly preparation in a reactor tube and transfer in a nitrogen filled glove box to an EPR tube failed. Next, some samples were prepared in^situ. EPR tubes were loaded with ated. The tubes mtorr of dehydrated zeolites and evacu were then filled with argon gas and sealed A pink approximately 50 off with a centers generated in these tubes a couple of days. Quartz flame. Color remained sometimes up to color was generated in zeolite NaY and a purple color was generated in NaX. obtain EPR spectra of these Attempts to samples failed and no further work was done due to lack of time. It has been reported 1 81 that tetrahedral sodium centers, due to Nag 5+ the pink color comes from N a ^ +. The purple color is centers. Attempts to generate a color center in KY zeolite (pre pared from repeated exchange of NaY with KC1 solution) also failed. R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 79 Treatment of the Na zeolites with microwaves without argon present resulted in no color centers. At high mi crowave powers (100 Watts), decomposition of the zeolite to A1 and Si occurred. 2.11.8 Inert Atmosphere Dry Box Procedures Many of the samples that were prepared were stored in a nitrogen filled dry box. This box was purified almost daily by recirculating the nitrogen atmosphere over a trap system containing an oxygen and a water trap. This trap was regenerated every few months by heating it to 250°C in hydrogen for several vacuum pump. hours followed by evacuation Dishes of phosphorus pentoxide with a were sta tioned in the dry box to react with small amounts of water vapor in the atmosphere of the box. The resultant phos phoric acid was removed from the box. 2.11.9 Fischer-Tropsch Reactions Samples prepared by the carbonyl procedure and the bimetallic procedure have been tested to measure their activity for hydrocarbon production by Li-Min Tau under the 91 . This work was done direction of Dr. Carroll Bennett in the Department of Chemical Engineering at the Universi ty of Connecticut. The reaction temperature The reaction mixture was 10? C0/H? . mL/min. was 285°C. The flow rate was 30 Typically, 25 mg of catalyst were used. R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 80 The samples prepared by the microwave discharge method were studied on a different tory. reactor system in our labora Our reaction line is a flow system using helium as an inert gas through purge. oxygen traps The helium and and water These were regenerated prior to hydrogen are passed traps for use. purification. Regulators in each of the lines allowed regulation of each of the gases sepa rately providing for reaction. one COrH^. the possibility of various These gas mixtures experiments used a ratio The flow rate was temperature was 250°C. of one to 30 mL/min and the reaction This temperature was chosen since a change in the FMR signal was observed above 250°C. This could be due to sintering of the metal. The reactor tube was a quarter and the catalyst inch stainless steel tube was supported on fine stainless steel mesh reactor tube was placed in a tube furnace ered by a temperature controller and the monitored on a digital thermometer. screen. The which was pow temperature was Analysis of the reac tant and product gases was done by an in line gas sampling valve and by two in-line The line was vented to gas septa for syringing samples. the hood. The experiments were done on the reactor line shown in Figure 15. R eproduced w ith perm ission o f the copyright owner. F urther reproduction prohibited w itho ut perm ission. 81 Figure 15: Reaction Line O o — CO vent a T lr t * . H- ■©— He c I a W at er b Oxygen c Fu r n ac trap trap R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. Chapter III RESULTS 3.1 INVESTIGATIONS OF SAMPLES BY FISCHER-TROPSCH REACTIONS 3*1.1 Catalysts Prepared By Microwave Reduction 18.104.22.168 Cobalt Catalysts Cobalt loaded by microwaves zeolites were prepared by of Co2 (C0)g on zeolites. were chosen as supports for the cobalt. the reduction Three zeolites A, a small pore zeolite, ZSM-5, a medium pore zeolite, and X, a large pore zeolite, were all loaded with the support pore size on cobalt. The influence of the selectivity of the catalysts was studied. The influence of the support pore size was shown by the hydrocarbon product distributions obtained with the cobalt catalysts. Cobalt on zeolite A (CoA) formed only methane as shown in Figure 16. Also in Figure 16 are the curves for the methane produced by cobalt on ZSM-5 (CoZSM-5) cobalt on X (CoX). ZSM-5 was nearly 100? at first but 40? after 10 minutes. methane. The methane production and by cobalt on fell to approximately CoX produced only a minor amount of Cobalt on ZSM-5, which has a larger pore size than A, also produced some larger hydrocarbons. _ 0? _ R eproduced w ith perm ission o f the copyright owner. F urther reproduction prohibited w itho ut perm ission. Figure CoZSM-5. 17 contains the product The effect of the pore production of methane and ethane. distribution size was shown for by the X is a large pore zeol ite and cobalt on X produced even larger hydrocarbons than cobalt on ZSM-5. Figure 18 contains the Propylene was the major product distribution product at Ethylene and ethane were also These catalysts showed long reaction the effect of the catalyst pore A small pore support small hydrocarbon whereas formed larger hydrocarbons. time. formed in small amounts. size on the hydrocarbons produced. formed a for CoX. a large pore support Further characterization of these catalysts is given in sections that follow. The percent conversion of CO to hydrocarbons cobalt catalysts is given in Figure 19. for the All of the cata lysts were very active initially but then decreased in ac tivity. The catalysts leveled off minutes but reaction did not become times. CoA was in activity after ten inactive after long the most CoZSM-5 had intermediate activity and active (60 min) catalyst. cobalt on X had the least activity. R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 84 Figure 16: Percent Conversion Cobalt Catalysts • 70 20 o 15 \CoA -60 o 10 I \CoZSM-5 -50 o 5 CoX TIME (min) R eproduced w ith perm ission o f the copyright owner. F urther reproduction prohibited w itho ut perm ission. 85 Figure 17: Co Catalysts Methane Production 1001 50CoZS M o CoX 30 TIME ( mi n ) R eproduced w ith perm ission o f the copyright owner. F urther reproduction prohibited w itho ut perm ission. 86 Figure 18: CoZSM-5 Product Distribution 100 o CH o 20 - TIME (m i n ) R eproduced w ith perm ission o f the copyright owner. F urth er reproduction prohibited w itho ut perm ission. 87 Figure 19: CoX Product Distribution 100 80-o q. 6 0- o 20- CH/ C,Hi n 20 TIME A0 60 (m in ) R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 88 22.214.171.124 Iron Catalysts Iron carbonyl, F e 2 (C0)g, and ferrocene, were loaded into various zeolites duction by ites. microwaves method to Fe(C^H^)2 and reduced by the re iron metal on the zeol Zeolites A, Y, X and ZSM-5 were chosen to study the influence of pore were compared size on these catalysts. to the cobalt catalysts. The results Fischer-Tropsch reactions were carried out on these catalysts. Ferrocene was loaded onto zeolite A and the sample was reduced to iron metal by the reduction by microwaves meth od. Figure 20 contains the percent conversion for this catalyst which similar to cobalt on A, produced only meth ane. The activity was high at first but then the catalyst became inactive after fifteen minutes. Ferrocene was also loaded onto zeolite ZSMi5. R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 89 Figure 20: Percent Conversion of Iron on A CONVERSION 40 30 PERCENT 20 10 I 10 f 20 30 TIME ( m i n ) R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 90 Figure 21 contains sample 30 (FeZSM-5) data for the percent which was prepared from the reduction by microwaves of ferrocene. iron on A in that it became Since ZSM-5 is a medium duced some lyst. This catalyst was similar to inactive after pore zeolite, larger hydrocarbons than Figure 22 conversion of shows the 15 minutes. this catalyst pro the iron on hydrocarbons A cata produced by FeZSM-5. Initially, mostly methane was produced. minutes, ethane and an unknown which appeared at a reten tion time of 1.3 minutes were formed. After 5 After 12 minutes, as the catalyst became less active, the unknown became the major product. Similar product distributions were formed with iron on zeolites X and Y. R eproduced with perm ission o f the copyright owner. F urther reproduction prohibited w itho ut perm ission. 91 Figure 21: Percent Conversion of Iron on ZSM-5 2 2 O o 20 . i— 2 - LlJ O cr LU CL TIME (mi n ) R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. Figure 22: Catalytic Properties of Iron on ZSM-5 100 80 o 60 AO o CH4 20 unknown 5 TIME 10 15 ( min ) R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 93 Two large pore zeolites, X and Y, preparation of iron loaded zeolites. were used Also, two metal pre cursors, Fe2(C0)g and ferrocene were used. tains the (FeX). data for the percent in the Figure 23 con conversion of sample 28 This catalyst was prepared by the microwave reduc tion of ferrocene on zeolite X. The products formed by this catalyst were not any higher in molecular weight than for the products from iron on zeolite shows the product distribution. was produced but the ethane minutes. ZSM^. Figure 2M Initially, mostly methane production dominated after 10 This catalyst also became deactivated after fif teen minutes as with the other iron catalysts. knowns were produced by this catalyst, however, No un^ unknowns were produced by iron on Y prepared from Fe2 (C0)g. R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. QU CONVERSION Figure 23: Percent Conversion of Iron on X 30 PERCENT 20 10 5 10 15 TI ME ( m i n ) R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 95 Figure 24: Catalytic Properties of Iron on X 100 CH 80 - o o 10 TIME 15 (mi n ) R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 96 Figure 25 contains a plot of sus time for sample 2H (FeY). by the microwave Figure 26 lyst. the conversion of CO ver This catalyst was prepared decomposition of Fe2 (C0)g on shows the hydrocarbons At first, produced by the major product was zeolite Y. this cata methane but the mixture became 50? ethane as the catalyst became inactive. Two unknown peaks were observed in the gas chromatographic analyses at retention times of 1.3 and 1.5 minutes. The first unknown eluted at the same retention time as the un known in the iron on ZSM-5 case. This catalyst had a longer life than the other iron catalysts but became inac tive after approximately 30 minutes. Figure 27 contains the percent of iron on zeolite X prepared by the waves of ferrocene. way as conversion for a sample reduction by micro This sample was prepared in the same the previous iron on X sample except that it was accidentally heated up to 275°C before the Fischer-Tropsch reaction. The resulting catalyst produced only methane. The percent conversion of this catalyst is very high. R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. Figure 25: Percent Conversion of FeX Sintered 70 (/) cr LxJ > Z 50 o o Ll I o Qd Ll I 30 CL 10 10 20 30 TIME ( m i n ) Reproduced with permission o f the copyright owner. Further reproduction prohibited without permission. 98 The iron catalysts cobalt catalysts all became inactive with remained active. catalytic properties of time but the A comparison the iron and cobalt of the catalysts is given in Table 9. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 99 TABLE 9 Catalytic Properties of Iron and Cobalt Catalysts Sample # 23 28 29 30 35 32 31 Sample % Conv FeX FeX FeA FeZSM-5 CoA CoZSM-5 CoX 113.9 3.4 21 .4 3.6 14.1 0.2 6.7 53.6 c 14.0 c 44.2 c 8.5 c 0.09 c C1/C2+ (a) - ♦ 9.0 0.2 - 0.3 * 0.54 d - a - after 2 minutes reaction b - after 10 minutes reaction c - after 1 minute reaction d - after 30 minutes reaction % conv - percent conversion of CO to products C.j /C2+ ~ ratio of methane to higher hydrocarbons Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 100 All of the previous catalysts duction by were microwaves method. prepared by the reduction were prepared by the re The following by catalysts hydrogen method tested as Fischer-Tropsch catalysts. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. and Percent Conversion of Iron on Y 5.0- PERCENT CONVERSION Figure 26: 1------------ 10 TIME 20 30 (m i n ) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 02 Figure 27: Catalytic Properties of Iron on Y 100 80 - CH 20 - T I M E (m i n ) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 103 3.1.2 126.96.36.199 Catalysts Prepared By Hydrogen Reduction Iron Carbonyl Catalysts Iron catalysts were prepared by the reduction in hydro gen of Fe(C0)j- on several zeolites was zeolites. employed in this zeolite Y (FeY) A wide variety of research but only iron on was tested as a Fischer-Tropsch catalyst. Figures 28 through 30 show some of the results of the re actions using this catalyst. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 28: Catalysis of Fe(C0)^Y 120 2700 - 2600 >_ 60- 2500 > o - 2400 ^ 0 0 0 ^ 9 9.QQQQIQGQQ,Q& Q Q 0 10 20 30 I I ME X 0 40 50 (sec) CO C H4 i co2 0 C2 H 6 0 c 3h 8 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Methane was the major product in Figure 28. by the catalyst was The percent conversion of CO 10.5. The activity of changed with time, as shown in Figure 29. tivity decreased for about 50 This ac seconds of reaction, these specific reaction conditions, FeY Initially, the catalyst was very active for methane production. crease again. as shown Lesser amounts of C02 , ethane and other hy drocarbons were also formed. in H2 formed by FeY, under and then began to in A maximum in activity appeared at about 300 seconds followed by a decrease in activity. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 06 Figure 29: Methane and Ethane Production of Fe(C0),-Y o O ro o JD O O r\l o Q> V) UJ <x> X o o rsl o I _D ^4X O ( a o Lf> o o o lT5 (6-ujLu/ujn) AilMiov Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 107 Hydrogen was passed seconds of reaction, from the catalyst. over the FeY catalyst, after 320 to observe the desorption of species Methane sorbed as shown in Figure 30. and several hydrocarbons de The methane peak consisted of a peak, a shoulder and a tail. Ethane, propane and bu tane also desorbed from the catalyst in lesser amounts. R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 1 08 F i g ur e 30: D e s o r p t i o n of F e ( C 0 ) ^ Y co Lf> O O o o eo o a> ui X cj3" 00 X CO UJ O 1 o <x> X O O CNJ CJ> <r X O o <T> O <£> (6-Ujiu/ujn) oo A1IAI10V R eproduced w ith perm ission o f the copyright owper. R udder reproduction prohibited w ith o u t perm ission o ( <3 109 188.8.131.52 Bimetallic Zeolite Catalysts Bimetallic zeolites were Scherzer and Fort 88 prepared by the method and were reduced in hydrogen. tion resulted in metallic iron in some cases. a mixture of oxidation states was obtained. also contained zinc, copper, troduced as another transition a metal ion. It Reduc Other times The catalysts metal element cobalt or ruthenium. of such as This element was in was not known whether the second metallic element was reduced to the metal. The ef fect of the second metallic element on the catalytic prop erties was studied. Table 9 contains a general results of a few of were studied. comparison of the catalytic the bimetallic zeolite catalysts that Column 2 shows the second was present initially in the catalyst. lysts involved the incorporation of metal ion that All of these cataFe(CN)^N0 p- synthesis and reduction at 400°C for four hours. Y was the zeolite used in catalysts 14, 18 and 22. was used in sample 15. sion of CO in H2 , lyst and the in the Zeolite ZSM-5 Table 9 lists the percent conver the number of active sites on the cata formation of bulk iron carbide for the dif ferent catalysts. Figure 31 shows the activity of duction of hydrocarbons. est percent sample 18 for the pro Sample 18 (CoFeY) had the high conversion of CO for the bimetallic zeolite R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 1 10 catalysts that were studied. lyst changed with time similar ite catalyst. The activity of this cata to the iron carbonyl zeol The activity of this catalyst also changed with temperature as shown in Figure 32. This Figure shows that activity increased as temperature increased. R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 111 Figure 31: Catalytic Properties of CoY - 2900 450 - 2800 - 2700 E 300 - 2600 - 2500 0 0 25 50 75 100 M E (sec 125 # CH^ X CO 0 c 2 h 6 ♦ C3 H8 9 C02 R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 1 Figure 32: CoY Activity Versus Temperature 900 300°C >300 271 °C o 0 100 TIME 150 200 (sec) R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 12 113 The activity of sample 22 time as shown in Figure 33. ane almost entirely. also changed with This catalyst produced meth Figure periment where the CO + (RuFeY) shows the data for an ex mixture was switched to helium after 60 seconds of reaction. When helium was passed over the catalyst, C02 was given off as shown by the growth of the C02 peak. Methane was also given off as shown by the peak in the methane curve at 85 seconds. A comparison of the catalytic zeolite samples results for the bimetallic is shown in Table 10. Characterization of these catalysts and experiments employed to ies that form these products distinguish the surface spec are presented in following sections. R eproduced w ith perm ission o f the copyright owner. F urther reproduction prohibited w ith o u t perm ission. Figure 33: Catalytic Properties of RuY 3000 240 2900 £160 2800 ~120 80o 2700 0 25 7 50 100 TI ME’ (s e c ) 9 CH4 0 CO X • c2 125 h6 C3 H 8 c4 H 10 R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 115 Figure 34 •* 200 RuY Reaction and Helium Purge He CO * H ■ 150 100 > o 0 20 40 TOTAL 50 TIME 50 100 (sec) • - ch4 x - C02 R eproduced w ith perm ission o f the copyright owner. F urther reproduction prohibited w itho ut perm ission. 120 116 TABLE 10 Catalytic Properties of Bimetallic Samples Sample # 1 14 15 18 22 Cation C > Co* Ru3 % Conv 10.5 2 2 9 5 # Sites -1-21 2.4 3.3 2.2 2.5 3.8 Cart 2 2 2 1 1 Y Y Y N N % conv - percent conversion of CO to products C.j /Cp+ - ratio of methane to higher hydrocarbons # sites - the number of active sites from shape of activity curve carbide - presence of iron carbide from M'dssbauer results R eproduced w ith perm ission o f the copyright owner. F urther reproduction prohibited w ith o u t perm ission. 1 17 3.2 SPECTROSCOPIC CHARACTERIZATION OF CATALYSTS 3.2.1 Catalysts Prepared By Microwave Reduction The samples prepared by the microwave discharge techni que did not show any Mossbauer signals. tration was below the detection instrument used. The iron concen limit of the particular For this reason, Mo'ssbauer data for the microwave discharge samples are not presented. Mossbauer spectra for iron were obtained 190 materials with a higher Recently, loading of . The infrared properties of the iron and cobalt zeolites were studied. peak for Before the microwave treatment, an infrared carbonyl was Fe2(C0)g samples. observed ples. 2000 cm 1 for the A doublet at 2000 cm 1 was observed in the COgCCOjg zeolite samples. no signal at was observed at After microwave treatment, this frequency for these sam Also after microwave treatment, samples were stud ied by ferromagnetic resonance. tra are shown in Figure 35. Some representative spec Shown are the spectra and g apparent values for an iron on -160°C (a) zeolite Y (FeY) and room temperature (b). sample at The g values were different at the two temperatures. R eproduced w ith perm ission o f the copyright owner. F urth er reproduction prohibited w itho ut perm ission. 11 8 Figure 35: FeY FMR Spectra o o O CO o <Nl II cn HP/„XP R eproduced w ith perm ission o f the copyright owner. F urther reproduction prohibited w itho ut perm ission. 11 9 A plot of the g apparent value versus shown in Figure 36 for the FeY sample. of inflection at room temperature. temperature is There was a point A plot of the linew- idth versus temperature is shown in Figure 37. The linew- idth decreased with increasing temperature. R eproduced with perm ission o f the copyright owner. Further reproduction prohibited w ith o u t perm ission. 1 20 Figure 36: FeY g Value Versus Temperature o IX) o co <_> UJ cr o Z> i— < cr iu o CL 00 2 : UJ o CD R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 1 pi Figure 37: FeY FMR Linewidth Versus Temperature o (— S UJ o VI 9'i O'I ( 9 M ) H 1 Q I M 3 N 11 R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 122 Representative zeolite X at plot of the ferromagnetic spectra 25°C and -160°C are shown in for cobalt on Figure 38. A g^-apparent value versus temperature same sample is shown in Figure 39. for this A plot of the linew- idth versus temperature is shown in Figure ^0. R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. Figure 38: FMR of CoX O O to LO CNJ o X CM CO CM H P /' . X P R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. Figure 39: CoX g Value Versus Temperature o vo o . CO LU cr Z) ■o I— < ct LU Q_ o 2: ■ 00 UJ o ■ VO ddD R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 125 Figure 40: CoX Linewidth Versus Temperature o o CJ oo o UJ cr -- o D < cr LU o °- 00 X ' LU O <£> — 1-------- 1------- H- 07 S'l O'l (9>l) H 1 Q I M 3 N H R eproduced w ith perm ission o f the copyright owner. F urth er reproduction prohibited w itho ut perm ission. 12 6 Table 11 lists preparations the value of iron of g and cobalt All of these samples were reduced crowaves method. room temperature. on alumina, apparent for on different several supports. by the reduction by mi These g apparent values were measured at Iron and cobalt carbonyls were placed titania and silica tion by microwaves method. and treated by the reduc Ferromagnetic resonance spec tra were obtained containing several peaks. The g values were very large compared to the other samples. R eproduced with perm ission o f the copyright owner. F urther reproduction prohibited w itho ut perm ission. 127 TABLE 11 Values of g Apparent Sample # Metal Precursor 26 Fep (C0)q Fep(C0)q Fep(CO)q Fe,(CO)' 27 Fep(CO)q 28 FetC,. H . U 23 24 25 29 30 31 32 33 34 36 37 Fe<c|H|)| Co 2 (C01 q COp(C0)o COq(C0)o COq(CO)o Co~(C0)p Fe^(CO)° Support Y X ZSM-5 SiOp TiCu X 2 A ZSM-5 X ZSM-5 SiO? TiOp HY B g(apparent) 2.08 2.08 2.08 2.22 2.18 2.08 2.02 2.04 2.18 2.19 2.32 2.55 2.17 2.08 B - bentonite R eproduced with perm ission o f the copyright owner. F urther reproduction prohibited w itho ut perm ission. 128 3.2.2 184.108.40.206 Catalysts Prepared By Hydrogen Reduction Iron Carbonyl Catalysts Fe(C0)j- was deposited on several zeolites. Mossbauer spectra of the untreated samples were obtained. These re sults gave information on the oxidation state of the metal on the catalyst. these samples. Table 12 contains the Mossbauer data for The samples were exposed to air and pelle- tized before the experiment. The iron carbonyl zeolite samples blimation under vacuum. low in color. were prepared by su The products were initially yel Heat was frequently given samples when exposed to air. samples turned brown. dation of the iron. off from these When heat was given off, the This could be an indication of oxi Column 1 contains the sample numbers and column 2 lists the zeolites used in the samples. value of the isomer shift (IS) these samples. or the center is given in column 3 for The isomer shift is the distance of a peak of quadrupole split peaks point or zero point. Our from a reference reference point was the center point of the six line pattern of metallic iron. given a value The of zero mm/sec. Column 4 is the quadrupole splitting (QS) for the sample. reduced samples, This was the value of For the un this was merely the distance between the peaks in a doublet. R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 129 TABLE 12 Iron Carbonyl Samples, Unreduced Sample # Zeolite cm on.=r invo b- Y X A HM NaM NaZSM-5 HZSM-5 IS(mm/sec) .40 .38 .45 .40 .43 .45 .43 QS(mm/sec) .80 .95 .90 .90 .85 .90 .95 M - mordenite R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 1 30 These iron carbonyl loaded zeolites drogen at temperatures up to 500°C. were heated in hy The samples were cooled to room temperature and analyzed by Mossbauer spec troscopy. The results of these Mossbauer studies are giv en in Table 13- Column 4 is an additional column which contains the hyperfine value that was calculated for these samples. This i3 a measure of the magnetic field strength in a sample. This can be referenced to a value of 330 kOe for alpha iron metal 184 . Figure 41 contains a Mossbauer spectrum of Fe(CO)^ decomposed on zeolite Y. This sample produced a six line pattern centered at zero. R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 131 TABLE 13 Iron Carbonyl Samples, Reduced imple # Zeolite support IS (mm/sec) 1 2 3 4 5 6 7 Y X A HM NaM NaZSM-5 HZSM*-5 -.09 -.08 -.01 0 J .01 -.01 .03 H (kOe) 339.0 3^0.6 329.7 335.9 326.6 329.7 335.9 M - mordenite R eproduced with perm ission o f the copyright owner. F urther reproduction prohibited w itho ut perm ission. 1 32 Figure : Mossbauer Spectrum of Fe(C0)^Y R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 133 o UJ CO >- o o -I UJ CM CM I <O I CM CM CO co CO i N 3 0 a 3 d NI 1 0 3 3 3 3 R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 1 31* Infrared spectroscopy (IR) was employed to study the carbonyl groups on the iron carbonyl zeolite samples. fore reduction, 1985 and 1960 IR peaks were seen at 2120, cm 1 . These peaks correspond groups in the samples. also observed. ites were 2019, to carbonyl Characteristic zeolite peaks were After reduction, studied by 2052, Be the iron carbonyl zeol infrared spectroscopy to determine whether any carbonyl was present from the metal precursor. No carbonyl groups were detected by infrared spectroscopy. The infrared signal for CO that was seen before reduction was absent after reduction. The electronic properties of the iron loaded zeolites were then studied by ferromagnetic resonance. zeolites, after reduction of the gen, um. The iron iron carbonyl by hydro were loaded into quartz tubes and sealed under vacu Ferromagnetic resonance spectra temperatures between -160°C to 250°C. served for the iron loaded were obtained at No peaks were ob zeolites after hydrogen reduc tion. The particle electron size of microscopy. the metals Samples were transmission electron microscopy tron microscopy (SEM). (TEM) was then prepared studied by for both and scanning elec The particular transmission elec tron microscope used had a much higher magnification than the available scanning electron microscope. For this rea- Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 135 son, more TEM studies were done. is shown in Figure 42. 140,000X magnification. This A sample TEM micrograph was a zeolite This particle sentative of the other particles was fairly repre studied. Fe(CO),. on zeolite Y after reduction. particle at The sample was The tiny black par ticles on the zeolite are the particles of iron. erage size of these iron particles was 70 The av to 100 stroms. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Ang 136 Figure 42: TEM of Fe(CO).-Y o Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 137 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 138 The iron zeolite catalysts by hydrogen of iron carbonyl were studied by Mossbauer spectroscopy. iron carbide was formed. spectrum prepared from the reduction for iron on This was after reaction to determine if any Figure 43 contains the Mossbauer zeolite Y after five minutes Fischer-Tropsch reaction. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. of 139 Figure 43: Mossbauer of Fe(C0)^Y Carbide Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 140 1N33U33 NI 133333 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1111 220.127.116.11 Bimetallic Zeolites Table 14 contains Mossbauer data for the OO pared by the method of Scherzer and Fort . ites were loaded with two metals, The reduction of iron was are reproductions of samples 15 through 22 these samples are our own variations. on zeolite All of NH^Y except on HZSM-5 and NaZSM-5. the Mossbauer signal of the signal before reduction. not show a Mossbauer signal for ter reduction. one of which was iron. Samples 8 through 14 OO the work of Scherzer and Fort and were prepared the predominant These zeol studied. numbers 15 and 16 which were data are for samples pre- for The anion which was Sample 22 did iron either before or af Energy dispersive X-ray analysis results indicated that the iron concentration was less than M . R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. TABLE 14 Bimetallic Samples, Unreduced Sample # 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 Cation Fe2 Fe2 Co, Co, Ni? Cu'l Znp Cu^ Cu, f4 Co, K12 ?4 Zn, Ru Anion Precursor K.Fe(CN)fi (NHj.) j,FeiCN)/K^Fe(CN) /(NHj)11Fe(CN)fi (NHjKFeCCN)? Na?Fe(CN) NO Na^Fe(CN )EnO Na^Fe(CN)^NO NapFe(CN)^NO NapFe(CN)^NO NapFe(CN)^NO NapFe(CN)^NO NapFe(CN)^NO K~Fe(CN)r Na^Fe(CN)°N0 IS^ - 0.10 -0-05 0.0 -0.05 -0.05 - 0.20 0.20 -0.15 0.20 0.0 0.20 - - - 0.20 0.35 - 0.10 Samples 8-14, 17-22 were on zeolite Y Samples 15, 16 were on zeolite ZSM-5 a values in mm/sec R eproduced with perm ission o f the copyright owner. F urther reproduction prohibited w itho ut perm ission. 1M3 The bimetallic zeolite samples were reduced in hydrogen at M00°C for four hours. were taken All of to measure the samples M’ o ssbauer peaks, Mossbauer spectra of the samples the oxidation showed the presence of except for samples sample 22 which had no peaks). Mossbauer spectra which state of the iron. two sets of 13 and 1M (excluding Samples 13 and 1M produced contained only the six line pat tern centered at 0 mm/sec indicating the formation of iron metal. All of the other bimetallic zeolites produced spectra containing the six line pattern and a doublet cen tered at 1.2 mm/sec, which indicates ferrous ions present. The Mossbauer results for the bimetallic samples after reduction in hydrogen are given in Table 15. R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. are 1 ix 4 TABLE 15 Bimetallic Samples, Reduced Sample # 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 Cation Anion Precursor Fe ll Fe * Co ll Co 9* Ni * Cu t Zn % Cu p Cu % Fe i Co Ni % Pd Zn , Ru 6 K.FeCCN), (NHZKFeCCN), K^Fe(CN)/- 6 (NHjb,.Fe(CN), (NHZKFeCCN)? Na^FeC CN),-N0 Na,Fe(CN)^N0 NapFe(CN)^N0 NafFe(CN)XNO Na,Fe(CN)^NO Na~Fe(CN)E n O Na~Fe(CN)EnO Na^Fe(CN)E n O Kf Fe(CN)5 Na£Fe(CN)°N0 IS^ H— -0.08 -0.03 -0.03 -0.09 -0.05 -0.03 0.03 0.0 0.01 -0.01 0.0 -0.04 0.03 -0.04 340.6 337.5 337.5 336.5 331.3 323-5 320.4 311-4 322-0 322-0 33 J.3 244-1 312.7 334.4 Samples 8-14, 17-22 were on zeolite Y Samples 15, 16 were on zeolite ZSM-5 a in mm/sec b in kOe R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 145 The Mossbauer spectrum of sample Figure 44. number 18 is shown in The major peaks formed a six line pattern for metallic iron. A doublet for ferrous ions was also pres ent . R eproduced w ith perm ission o f the copyright owner. F urther reproduction prohibited w itho ut perm ission. 1 46 Figure 44: Mossbauer Spectrum of CoY R eproduced with perm ission o f the copyright owner. F urther reproduction prohibited w itho ut perm ission. 147 i ---------------1-------------- 1-------------- 1---------------1--------------- r _ J_________I_________I_________ I_________ I--------------- L o — <m to m l N 3 0 3 3 d NI 1 0 3 3 3 3 R eproduced w ith perm ission o f the copyright owner. F urther reproduction prohibited w itho ut perm ission. 148 Infrared spectroscopic studies of ites were performed iron. were to study Before reduction, observed. groups, These respectively. also observed in these the bimetallic zeol the ligand IR peaks peaks groups on the at 2205 and 1950 cm correspond to CN and NO Characteristic zeolite peaks were samples. After reduction there were no signals observed for CN or NO in the samples. The characteristic zeolite peaks were still present. The bimetallic zeolites were loaded into quartz tubes after reduction in hydrogen and sealed under vacuum. ferromagnetic resonance spectra of these samples tained at various temperatures. The was ob The signals were the same as in the iron carbonyl zeolite samples. A straight line with no peaks was recorded. The reduced bimetallic zeolites electron microscopy to determine the metals. These samples had a were also studied by particle size of the large particle size similar to the reduction by hydrogen samples. The iron particles in these samples were 50 to 80 Angstroms. 18.104.22.168 Aluminoferrisilicate Zeolites Table 16 contains Mossbauer silicate zeolites. The data for the aluminoferri- signal for sample 48 is for the zeolite which was dried overnight at 110°c in an oven. The sample 49 signal is for the same zeolite after calci- R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 1 49 nation at 550°C in air for 6 hours. The signal for 48 is a singlet and for 49 a doublet. R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 1 50 TABLE 16 Aluminoferrisilicate Zeolites, Mossbauer Results Sample # IS(mm/sec) 48 49 Fe(II)Y Fe(III)Y 0.2 0.3 1.2 0.4 Fe(n)Y from Huang and Anderson Q S (mm/sec) 0.7 2.4 0.86 79 R eproduced with perm ission o f the copyright owner. F urther reproduction prohibited w itho ut perm ission. 151 The aluminoferrisilicate drogen at 400°C and 1I50°C. had a Mossbauer in hy^ Before reduction, the zeolites doublet with an isomer mately 0.3 mm/sec. ions. zeolites were reduced shift of approxi This signified the presence of ferric After reduction, the zeolites had a doublet with an isomer shift of 1.0 mm/sec due to ferrous ions. bauer results for the The Moss aluminoferrisilicate zeolites after reduction are given in Table 17. R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 152 TABLE 17 Mossbauer of Reduced Aluminoferrisilicates Sample £ 48R1 48R2 49R3 Fe(II)Y Fe(III)Y Reduction IS temp. (mm/sec) 400 450 400 - 1 .0 1.0 1.0 1.2 0.4 QS (mm/sec) 2.1 2.0 1.9 2.4 0.86 R1 - 48 reduced 400°C R2 - 48 reduced 450°C R3 ~ 49 reduced 400 C Fe(n)Y from Huang and Anderson R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 153 Differential thermal analysis was employed in the study of the aluminoferrisilicate zeolites to observe of water with heat and that might occur. 45 and 46. to study any phase transformations A few of the runs are shown in Figures These experiments showed the loss of water as the zeolites were heated. ing off of the loss Analysis of the substance com the zeolite was not done but the temperatures suggest that the substance was water. R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w ith o u t perm ission. Figure *15: DTA of Aluminoferrisilicate o LOt"- EMPERATURE (°C) o LDLD O lo - o LO oxe iv opue R eproduced w ith perm ission o f the copyright owner. Further reproduction prohibited w itho ut perm ission. 1 55 Figure 46: DTA of Aluminoferrisilicate o LO- o o LO UD LLj <—> rv- lO- < O ce ld - 2 o LLi ID CNJ O lO- O LO 0X0 I V * opue Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 56 The types of ferric zeolites was studied with ions in the aluminoferrisilicate ferromagnetic resonance. ures 47 and 48 show some examples of the results. Fig Signals were seen for framework ferric ions and non^-f ramework fer ric ions. The framework ion signal is labeled A and the non-framework signal is labeled B. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 157 Figure 47: FMR of Aluminoferrisilicate HP/..XP Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. FMR of Aluminoferrisilicate H (kG ) Figure 43: Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 159 3.2.3 Catalysts Prepared By Sodium Vapor Reduction Iron was ion^exchanged into several zeolites to be used in the sodium reduction experiments. Zeolites A, X and Y were employed These in these experiments. samples were studied by Mossbauer spectroscopy to observe the oxidation states. The results of these studies are shown in Table 18. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 160 TABLE 18 Ion-Exchanged Zeolites, Mossbauer Results Sample # 35 36 37 IS (mm/sec) .50 .50 .50 Q S (mm/sec) 1.0 0.9 0.9 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 151 During the vaporization of the could be seen production of a sodium, in the reduction tube. a purple color This could be the color center similar to those crowave experiments. The samples were in the mi This color faded quickly. reduced with sodium vapor and loaded into air tight Mossbauer containers in the dry box. bauer spectra were run to in the samples. observe the extent of reduction Before reduction, these samples showed a doublet with an isomer shift of 0.5 mm/sec. tion, iron on Y had an isomer shift of iron on zeolites A and X still proximately 0.5 mm/sec. Mossbauer pattern small doublet After reduc 1.3 mm/sec while had an isomer shift of ap Sodium reduction was ducted on sample 3 (Fe(CO)j. on six line Moss with an isomer A). also con This sample showed a centered at 0 mm/sec shift value of plus a 1.2 mm/sec. Sodium reduction was also done on a bimetallic zeolite ca talyst. Sample 13, which contained copper and iron on zeolite Y, was reduced and showed a doublet with an isomer shift of 0.4 mm/sec. The Mossbauer results for these sam ples are given in Table 19. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 62 TABLE 19 Mossbauer Results After Sodium Reduction Sample # 35 36 37 3 13 IS (mm/sec) 1.3 0.4 0.5 0.0 0.4 QS (mm/sec) H (kOe) 2.6 1 .0 1 .0 1 .0 322.0 F Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 163 Potassium vapor samples. reductions were performed on similar Some reduction of the iron was detected but the samples were not reproduced due to lack of time. tassium vaporized at a lower temperature than The po the sodium so that the experiments were run at a lower temperature. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Chapter IV DISCUSSION 4.1 FISCHERFTROPSCH RESULTS 4.1.1 Catalysts Prepared By Microwave Reduction 22.214.171.124 Cobalt Catalysts The cobalt zeolite catalysts that microwave reduction of the support which of cobalt carbonyl showed pore size on the the Fischer^Tropsch reaction. contained reduced small hydrocarbon. 56 The small pore cobalt formed The critical molecu- all have a critical of 4.2 Angstroms (NaA). tive for a long time and n- diameter of be Zeolite A has a pore size This effect particles are very small. Ethane, Methane could fit inside of A but was inside the zeolite cage. vated. a The size of the cage would not permit tween 4.6 and 4.9 Angstroms^. ethane could not. zeolite A only methane, of methane is 4.00 Angstroms. propane and n^butane the effect hydrocarbons produced in a larger hydrocarbon to be produced. lar diameter were prepared by the indicated that the cobalt This implies that the metal This catalyst also remained ac did not appear to become deacti Products did not block the pores and cause deacti vation . - 164 - Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 65 The larger products. pore zeolites produced larger Cobalt on ZSMi5, which is a larger pore zeolite than A, formed methane and ethane. Ethane is a larger hy drocarbon than methane and requires talyst pores. can the larger hydrocarbons. which is a larger pore takes up more space formed propy in the zeolite. size of the hydrocarbon product this to be The large formed. sites were inside of This indicated that the zeolite cages. The metal particles must therefore be very small. The hydrocarbons once formed were free to desorb from the catalyst. sites were on The hy zeolite cages and were lim ited in size by the volume of the cage. active metal The was related to the physi cal size of the pore in the catalyst. drocarbons were formed in the on X, Propylene is larger than eth in zeolite X allowed the active metal Cobalt zeolite than ZSM-5, lene, ethylene and ethane. pore size more space in the caF ZSM-5 has a pore size of 5.5 Angstroms and accommodate ane and hydrocarbon the outside of then the small pore catalyst would If the the catalyst, form the same size hy drocarbons as the large pore catalyst. The activity of the cobalt catalysts changed during re action which implied time. that the catalyst was At these temperatures, al atoms could move around increase in particle size. changing with it is possible that the met in the catalyst This was not and possibly studied except for ferromagnetic resonance experiments of the spent cata Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 66 lysts. Cobalt on A and ZSM-5 produced methane and ethane which are saturated hydrocarbons, whereas cobalt on X pro duced propylene and ethylene carbons. which are unsaturated hydro The metal particles on zeolite outside of the zeolite due to A may be on the the small pore size of A. There might have been another effect influencing the prod ucts in the case of zeolite X besides shape selectivity. Zeolite acidity is one possibility. The physical size of the hydrocarbon products was determined by the of the degree of saturation catalyst but the been determined by some other factor. pore size might have Catalyst acidity or some reaction condition such as reactant gas concentration could have an effect. The exact reason for the formation of unsaturated hydrocarbons is not known. *126.96.36.199 Iron Catalysts The iron zeolite catalysts produced by the reduction by microwaves of Fe2 (C0)g fect of the catalyst pore size on the size carbons produced. like cobalt and ferrocene also showed of the hydro Iron on zeolite A produced only methane on A. The shape of the graph showed only one peak. after thirty minutes. tion of bulk the ef percent conversion The catalyst became inactive This is probably due to the forma iron carbide as seen in the other Fischer- Tropsch reactions with iron zeolite catalysts. Verifica tion of this theory by Mossbauer spectroscopy could not be Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 167 done due to the low concentration of iron present. on ZSM-5 produced methane, Iron ethane and an unknown species. This unknown was possibly an oxygenated species since iron can produce such products. The identity of was not determined but methanol, ethanol and acetone did not have retention times equivalent retention time for the unknown to the unknown. the unknown was 1.3 minutes The at a flow rate of 25 ml/min of helium using Alltech VZ-10 columns at an oven temperature of 50°C. Methanol, ethanol and ace tone are not separated by VZ^IO columns and elute with the air peak at 0.32 minutes under these conditions. The un known’s retention time of 1.3 minutes is between the peaks for ethylene (1.07 minutes) and propane (1.87 minutes) un der these conditions of flow If this peak rate and is for an oxygenated species, large molecule that is similar Iron on ZSM^5 appeared it must be a to a hydrocarbon since the unknown was separated from the air umn. oven temperature. peak by the VZ-10 col to have two active sites, similar to other iron catalysts in this dissertation. Fischer-Tropsch reaction about 5 minutes these specific showed a formation. The reaction conditions. probably formation of iron firmed since Mossbauer to the low conversion maximum and a second maximum at quickly became deactivated, at 12 minutes under The catalyst then due to iron carbide carbide was spectra could not be amount of iron present. The It not con obtained due is possible that Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 168 iron carbide could have that the iron formed in the zeolite could have migrated to the pores or surface to form iron carbide there. Two large pore zeolites were the iron catalysts. products formed by These zeolites were Y these catalysts though both catalysts the same structure. and X. The were different even included iron and were reduction by have different also used as supports for microwaves method. Si/Al ratios The zeolites and acidities but the same The particle size of the iron was the same for both catalysts as shown by ferromagnetic resonance. pore size of the zeolites was the same, difference in the products was determined have been bound Perhaps the by the precursor or the acidity of the catalyst. cursors could The so that shape se lectivity would form the same size products. zeolite. prepared by metal The metal pre at different sites in the Different binding sites can have varying effects on the metal because of different binding strengths. Iron on X was prepared from the reduction by microwaves of fer rocene. This catalyst formed larger hydrocarbons case of cobalt on X. duction by methane and were produced as ethane. were formed No in the Iron on Y was prepared from the re microwaves of ethane and two unknowns. Fe^CCO)^. It formed methane, One of the unknowns was probably the same unknown as was formed by iron on ZSM-5. Both of these catalysts became inactive with time. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 169 4.1.2 Catalysts Prepared By Hydrogen Reduction 188.8.131.52 Iron Carbonyl Catalysts Fe(CO)j- was placed hydrogen, on several zeolites and reduced in but only the iron on zeolite Y was studied as a Fischer-Tropsch catalyst. All of the catalysts prepared by this method had similar states. The samples all contained large particles of iron metal. particle sizes and oxidation The iron on Y catalysis results were taken as rep resentative of samples prepared by this technique. The iron catalyst prepared by the reduction by hydrogen of iron carbonyl on zeolite Y had a fairly high conversion of CO. 28. The major product was methane as shown in Figure The reasons for this high methane production were the reaction conditions. These reactions were run at ?85°C and a reaction mixture of 10? CO in H2 which represent methanation conditions. Temperatures above the formation of methane. 250°C promote Hydrocarbon chain formation is inhibited at higher temperatures since molecular motion is increased and surface groups are temperature increases. bound less Methane desorbs from the catalyst before any chain growth can occur. drogen present and less carbon ments than in the reactions ples. The reactant strongly as There is also more hy present in these experi on the microwave reduced sam gas mixture is 10? CO the reactions with the microwave in whereas reduced samples used 50? Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 70 CO in . Lower amounts of promote methane formation. CO in the Iron on reactant mixture Y formed other prod ucts than methane but in smaller concentrations. crowave reduced samples were run at 250°C mixture of 50? CO in The mi and a reaction These conditions promoted chain growth of the hydrocarbons. Significant amounts by iron on Y as of the by-product CO^ indicated by Figure 28. synthesis ideally involves the and water. The oxygen from CO were formed Fischer-Tropsch production of hydrocarbons is reacted to form water. This oxygen can also react to form C02 or oxygenated spec ies such as methanol. oxygenated species. Iron catalysts can produce a lot of When hydrocarbon chain growth is de sired, loss of carbon to a by-product such as CO,, is unde sired. imum. The amount of CO^ formed is usually kept at a min There also appeared to be at least two active sites on the catalyst as suggested curve in Figure surface of 30. by the These sites must be the zeolite since electron indicate that the iron particles were the zeolite cages. in hydrogen active initially One site show the microscopy results too large to fit in shape selectivity reduced catalysts did. and probably was became active seconds for on the outside For this reason, the catalysts reduced did not that the microwave hydrogen desorption One the clean with time with these reaction conditions. site was iron metal. a maximum This effects at 300 could have Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 171 been the formation of an active carbide species. Surface carbides that form early in Fischer-Tropsch reactions have been shown to be active gresses, inactive bulk catalysts. carbides tion of the catalyst. The stantly reduced changing from carbides to time. form and cause deactiva catalysts appeared to be con bulk carbides. Bulk As the reaction pro metal to active FeY became iron carbide formation Mossbauer studies at surface deactivated with was observed the point where the in the catalyst became inactive. This is shown in the Mossbauer spectrum in Fig ure ^3- The desorption studies with three portions. showed a methane curve The three portions (peak, shoulder and tail) might be related to the active sites observed in the reaction product curve. desorption curve could same types of three portions in the be due to three on the catalyst that desorb be the These as methane. species but different species They could also on sites with varying binding strengths. 184.108.40.206 Bimetallic Catalysts Many samples were prepared which contained iron and an other metallic element on a zeolite. Tropsch catalysis were selected of reduction. Samples for Fischer- according to completeness The samples containing copper and zinc con tained completely reduced iron metal. chosen with variations in the Other samples were second metallic element and Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 172 the zeolite. The other samples contained cobalt, rutheni um and zeolites Y or ZSM-5. These samples were believed to be representative of the sample technique. The bimetallic catalysts showed the ond metallic element on the effect of the sec percent conversion of CO, on the number of active sites on the catalyst and on the for mation of bulk iron carbide. This is shown in Table 10. The second metallic element did not, unfortunately, it the formation of large metal shown in the electron of iron are large particles of microscopy results. and therefore must surface of the zeolite. These be on inhib iron, The particles the outside catalysts do not show the shape selectivity of the microwave reduced catalysts. catalysts that contained iron and balt and ruthenium. zinc or The rea the Fischer-Tropsch activity of co The catalysts that contained iron and copper had low also produced The ruthenium or cobalt had high activity as catalysts as shown in Table 10. son for this could be as activity. catalysts with Cobalt only one and ruthenium active site, as shown by the shape of the reaction products curves in Fig ures 31 and 33* to the There were formation of another there were two no increases in activity due It is possible that active sites that were both active at the start of the reaction. site. The shape of the reaction product curve would only indicate more than one site if the activ ities had maxima at different times. This is a possibili Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 73 ty that was not investigated. carbide species was not detected taining cobalt and ruthenium. allic elements also carbide. for the catalysts con The presence of these met inhibited the formation of The helium titration shown in Figure 34 was bulk iron of the ruthenium catalyst conducted at the reaction tempera ture and showed the formation ide. The formation of an active of methane and carbon diox The carbon dioxide might indicate that there were CO and 0 groups on the catalyst during reaction. formation might indicate that there groups on the catalyst. The methane were also CHx and H Under these particular reaction conditions it appeared that there were more CO groups than CHx on the catalyst since more carbon dioxide was formed. C02 could formed from the also have been surface carbon with 0 groups. catalysts and the formation of combination of The types of groups on the bulk iron carbide inferred by the catalytic results. can be A more direct method of analysis of these types of systems was done using spec troscopy . 4.2 SPECTROSCOPIC CHARATERIZATION OF CATALYSTS 4.2.1 Catalysts Prepared By Microwave Reduction The concentration of the iron was fairly low in the ca talysts prepared by reduction Mossbauer spectra could be by microwaves obtained. tron microscopy determined the iron to so that no Results from elec be less than 1* in Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 174 the catalyst. This was still enough metal to catalyze the conversion of carbon monoxide and cobalt to hydrocarbons. The iron carbonyls were completely decomposed carbonyl peaks were observed ter microwave treatment. since no by infrared spectroscopy af The ferromagnetic resonance also indicated that the decomposition was complete since ferro magnetic metal particles were formed. particles was smaller less than since the The size of these 20 Angstroms catalysis results and probably even suggested that the metal was inside the zeolite cages. Ferromagnetic resonance was iron and cobalt on supports, performed for the supports in Table 11. reduction. The g values cobalt on the different iron and The g apparent values measured by ferromagnetic resonance were the suggesting that smallest on the zeolites the metal particles zeolites than on the other supports for iron on X but g = 2.22 for iron indicate that the metal particles than on zeolite X. of such as silica and titania, that were prepared by microwave were compared on samples were smaller on the (for example g = 2.08 on SiO^). This may were bigger on silica The g apparent values were very close for the iron prepared from ferrocene and for the iron pre pared from Fe^CCO)^. This indicates that small particles can be prepared from different metal precursors. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 175 These ferromagnetic species were unstable. on X air. catalyst was pyrophoric The cobalt and smoked when exposed to The oxidation of these small high surface area par ticles appeared to be very exothermic. The small metal particles generated by the reduction by microwaves technique prove that the the carbonyl compounds without microwaves might temperature sintering the metal. create local hot of the microwaves decompose spots but sample during The the overall sample preparation is room temperature, as measured by a thermocouple. The microwave discharge experiments had the number of problems with reproducibility. ites prepared by the reduction by The cobalt zeol microwaves of carbonyl were fairly easy to reproduce. prepared by reduction by microwaves of iron carbonyl were This could be due nature of iron metal to form iron oxide. oxygen or water oxidation of the metal). could causesintering and low powers could compose the metal complex) to Any trace amount The thoroughly dehydrated supports, microwave power (high powers sure tothe reactive contaminate these samples. samples were dependent on composition of supports cobalt The iron zeolites harder to reproduce. of oxygen or water could greatest or de fail to de and sample handling (any expo vapor Often results in immediate the contamination of the sample was not evident until the Fischer-Tropsch reactions Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 176 when the catalyst was found to be inactive. Repetition and careful attention to detail resulted in increased re producibility in these samples. The microwave discharge samples often seemed heterogeneous before microwave treat ment. The side of the zeolite closer to the metal complex and away from the vacuum pump appeared darker. the metal deposited on this side, Initially, but as time progressed the rest of the zeolite became saturated with the complex. A few times after microwave treatment, the zeolite parti cles appeared blacker on the top or on the surface. did not seem to affect the This catalytic activity of the sam ples. The initial Fe^CCO)^. microwave Carbonyl volatile enough to samples involved the species were chosen since sublime and easy enough use of they were to decompose. Reduction was not necessary since the iron was in the zero oxidation state. flow system and Fe(CO)^ was too Fe^CCO)^ F e ^ C C O ) ^ was also of the zeolites. (it sublimed was not volatile too large to fit in the in a enough. pores of some Fe2 (C0)g appeared to be volatile enough at 35°C) and small enough to The technique was successful in ticles on volatile to use zeolite Y as shown by preparing small iron par ferromagnetic resonance but the iron concentration was less than electron microscopy. merit study. Reaction studies as measured by were done but the percent conversion of the CO was fairly low. Other metal precursors were investigated. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 77 Experiments with iron samples. FeCl^ failed Ferrocene, however, tion of small metal particles. volatile than Fe^CCO)^. erature. to prepare which the pink of the argon did yield the produc Ferrocene was much more It sublimed readily at room temp The initial plasma was the carbonyls) any reduced purple (it was blue for made it harder to distinguish from plasma but long decomposition times resulted in total decomposition. 4.2.2 220.127.116.11 Catalysts Prepared By Hydrogen Reduction Iron Carbonyl Zeolites The iron carbonyl zeolites spectroscopy were studied immediately after sublimation carbonyl and before any further treatment. summarized in Table 12, on the zeolite. showed same as temperatures. The signal ions in zeolites. These studies, the condition of the iron was similar to that The iron as shown by the ferric The carbonyls were still infrared results, somehow changed. of probably was oxidized rather The iron Fe(C0)^L species where the L or the zeolite matrix.The Mossbauer results types of species have been reported 154-160 but the iron carbonyl could have formed an isomer shifts iron reported for iron carbonyl at low than remaining in the Fe° state. carbonyl had of the The Mossbauer signal for the iron carbo nyl was not the present, by Mossbauer . and quadrupole splittings for is an oxygen for these The range of the Fe(C0)^L Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 178 species is similar to the zeolites. The use of careful precaution prevented the results for our iron carbonyl thoroughly dehydrated supports and to exclude formation of air and water might this oxidized species. have The high temperature that was needed to reduce the iron carbo nyl also points to an oxidized shift and were not form of iron. quadrupole splitting the same served in as those for for the The isomer oxidized species the unreduced the Mossbauer spectrum after iron (ob reduction). The unreduced iron has an isomer shift and quadruple splitting very similar to ferrous ions. temperatures up to absence of with X and Y being the The isomer shifts zeolites were close to greatest. the iron signal. 0 mm/sec, This is shown in Table values for also different than the rest. environment in other smaller pore kOe. metallic iron quadrupole splittings and hyperfine iron on X and Y were haps the indicated that some unreduced iron. on all of the The pattern and the Reductions at temperatures below 500°C of ten resulted in 13* The six line any other peaks was produced. for iron 500°C. The reduction was done at X and Y was different zeolites and that effect Per than the was shown in Alpha iron has a hyperfine value of 330 Iron on zeolites A, mordenite and ZSM-5 gave hyper fine values close to that of alpha iron. gave hyperfine values closer to the value H is not known. Iron on X and Y 3^0 kOe. The experiments The reason for were done in Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 79 the in-situ Mossbauer reactor so oxygen or water occurred. ed for alloy formation that no contamination by- High H values have been report- 95 but that is not the case here since iron is the only metal present. The absence of any carbonyl peaks in the infrared spec tra of the reduced iron zeolites indicated that the carbo nyl was completely gone. Complete occur during reduction. not occur since the decarbonylation must Decomposition of the zeolite did characteristic zeolite peaks were still present. The iron carbonyl zeolite samples appeared at times to be heterogeneous before reduction (containing regions of higher and lower metal concentrations). samples appeared to have more iron the zeolite, where contact was These carbonyl at the top of initially made with the carbonyl vapor. Ferromagnetic resonance indicated that no ferric ions were present since ferric ions give a strong electron par amagnetic resonance signal due in the high spin state. The iron zeolite samples prepared from the reduction by hydrogen bulk metallic This was iron, to five unpaired electrons of iron carbonyl contained as indicated also proven by by the the electron straight line. microscopy results which indicated a large metal particle size. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 18.104.22.168 Bimetallic Zeolites The M6'ssbauer signals for the iron atoms tallic zeolites before reduction were ies. The anion component usually nal. Samples 8, in the bime for the anion spec gave the stronger sig 9 and 17 in Table 14 also had Mossbauer peaks before reduction with an isomer shift of 1.2 mm/sec characteristic of ferrous ions. The Mossbauer were similar with the same anion, with due the presence of the second metal. nal due to ammonium hexacyanoferrate fected by the second metal. p p^, with Fe is not , Co and Ni seemed to be unaf as the initial second ions. second metallic are probably still ions since these 2+ The Mossbauer sig It appeared in the same place still ions or if reduction did occur. Co small variations p^ known whether these reduce. results It elements are The zinc and copper ions are very hard to The potassium ferricyanide showed a singlet with and a doublet with Zn 2+ . The samples containing so dium nitroprusside showed similar Mossbauer signals except when Fe 2+ and Fd 2+ were present. palladium sample was the most Tne isomer shift of the positive value for the sam ples studied. These bimetallic zeolites reduced to The samples that reduced the 13 and 14 in Table 15. peaks for unreduced iron. varying degrees. most completely were numbers These two samples did Surprisingly, not show these two bime- Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. tallic zeolites had very Tropsch reactions. low activity All of the in the Fischer- other samples showed some amount of unreduced iron as well as metallic iron by Mossbauer spectroscopy. The isomer shift of all of the bime tallic zeolites was close to 0 mm/sec. The hyperfine val ues ranged from 294.1 kOe to 340 kOe. of H were for the side. The lowest values samples prepared from sodium nitroprus- The highest H values involved combinations of the iron anion species with iron or cobalt. Higher values of H can be an indication of alloy formation. Alloys of iron and cobalt in catalysts has been reported. These samples showed that the second metal influenced the degree of re duction of the electronic properties of the iron. iron and the It has already been mentioned that the second met allic element in the bimetallic zeolites affected the ac tivity and life of a catalyst. These samples involved a two Initially, a cation, such as Co method. , was exchanged into the 2like Fe(CH)^N0 was ex zeolite. Secondly, changed. When the anion exchanged into the zeolite, of two things an anion 2+ fold exchange must have happened. If it was one a true ex change, then it replaced an anion that was present in the _ p_ zeolite (N0^ or S0^ from the initial exchange). If this did not happen then the cation from the anion (K+ or Na+ ) must have been present somewhere in the zeolite in order to maintain a neutral charge. It is Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 82 not known which process actually occurred. The important fact was that the anion did go in and it attached to some thing (probably the transition metal cation) was not lost in the washing of anion that of the catalyst. exchanged into the zeolites it produced more so that it The amount was high since than 3% iron in the sample and since it could be detected by Mossbauer experiments. Before reduction, the anion complex such as Fe(CN)^NO was probably on the inside of the zeolite cage iron was exchanged into the zeolite. ion-exchange sites on the outside p- since 3% There are not enough of the zeolite to ex change 3% iron into the samples, therefore the anions must also be exchanging with internal ions must be on the inside sites. Some of the an of the zeolite before reduc tion. Before reduction, the peaks for CM and NO in the infra red spectra of these samples indicated that the complexes did exchange into the zeolites. ter reduction, The infrared spectra, af indicated that the complexes were decom posed, since no CN or NO peaks were observed. The oxida tion state of the initial cation was not known. The ferromagnetic resonance studies of ferric ions and the presence electron microscopy showed large. showed the absence of bulk iron metal. the metal particle size The to be The metal must therefore be on the outside surface Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 183 of the zeolite. The bimetallic zeolite catalysts did not show any influence of size selectivity on the hydrocarbons produced from CO like the microwave catalysts did. is further evidence that the metal This is on the outside sur face of the zeolite. 22.214.171.124 Aluminoferrisilicate Zeolites These zeolites 450°C. were reduced in hydrogen at 400°C and Before reduction, the Mossbauer signal was that of ferric ions. reduction, The results are the shown in Table 16. signal appeared to be for After ferrous ions. The results for the reduced samples are in Table 17. duction to the metal did not occur. sults were obtained Similar Mossbauer re with the dried and This suggests that the calcination is calcined samples. not a vital step to the reduction of the iron to the ferrous state. cination is a vital step in from the zeolite. for the presence Re the removal of The cal the template The uncalcined samples were not studied of the template or for residue from the template. The thermal analyses of ites shows several peaks. ably due to the loss of above are probably late. the aluminoferrisilicate zeol Low temperature peaks are prob water. The peaks at due to the decomposition 450°C and of the temp Above 700°C, the zeolite itself might be decompos ing . Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 184 11.2.3 The Catalysts Prepared By Sodium Reduction samples used in these experiments were from the ion-exchange of ferrous nitrogen. ions into zeolites under The Mossbauer experiments on these samples in dicated that ions. prepared the ferrous ions became oxidized to ferric Adjustment of the pH was attempted without success. The ferric zeolites were used periments. in the sodium reduction ex After reduction, iron on zeolite Y appeared to be ferrous ions but no metallic iron was detected. Iron on zeolites A and X appeared to be ferric ions as they did before reduction. Sample number 3 (iron carbonyl on zeol ite A) did reduce to form some metallic iron but some fer rous ions were still present. and iron bimetallic on zeolite ions after reduction. peared to state. Y) reduction of the never successfully accomplished. 13 (copper appeared to be ferrous The failure of the be in the oxidation The Sample number technique ap of the iron to the ferric original ferrous ions was The potassium reduction experiments appeared to have potential. The lower vapori zation temperature of the potassium could have caused less sintering than were incomplete did the and the sodium reductions. experiments were The results halted due lack of time. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. to 1 85 4.3 COMPARISON OF SAMPLE REDUCTION METHODS It important to compare reduction by hydrogen carbonyl zeolites and bimetallic zeolite samples), vapor reductions The various and reduction by a (iron sodium microwave discharge. reduction methods varied in completeness and quickness of reduction. 4.3.1 Completeness of Reduction The microwave discharge method was the most versatile and complete method of reduction. Iron and cobalt carbo nyls ferrocene on and organometallics could be reduced to the successful in such as metal. Hydrogen reductions were producing metallic iron from zeolites and in certain bimetallic produce small metal particles. 15 . iron carbonyl zeolites but failed to The iron carbonyl zeolites required a much higher temperature been reported zeolites for reduction than has This could be due to the formation of a Fe(CO)^/zeolite species. This species could be harder to reduce, especially if the iron is in an oxidized state. The degree of reduction of the anionic complex by hy drogen to metallic iron in the bimetallic zeolites was in fluenced by three factors. pendent on the initial First, cation. reduction of iron was achieved with initial cation. the reduction was de The highest degree of copper or zinc as the With these cations there was no detecta Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 186 ble unreduced iron. Different cations interacted differ ently with the iron complex. Perhaps the strength of the interaction influenced the reduction of the iron. The second factor complex itself. much more that influenced reduction was the Sodium nitroprusside, Na2 Fe(CN)^N0, was effectively reduced This complex even reduced at than the temperature other complexes. a lower temperature, used with the other effect could be due to the These ligands than the 300°C, samples. This ligands present in the sample. influenced the charge of the central iron atom, the coordination environment of the complex and per haps have varying leaving abilities due to their binding strength with the iron. The third important factor was the support. Reduction was easier on NH^Y than on either NaZSM-5 or HZSM-5. ple 13 differed from samples 15 port. Sample 13 showed complete reduction whereas 15 and 16 contained some and 16 only by Sam unreduced iron. This effect the sup could be due to the type and strength of sites to which the complex binds. Sodium vapor reductions failed reduced iron metal. of Fe *3+ to produce completely This was possibly due to the presence from the oxidation of Fe to reduce in zeolites. 2+ . Several others Ferric ions are hard 99 100 ’ have suggest ed that this is a difficult task. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 87 4.3.2 Length of Reduction Time The microwave discharge reduction was one of the quick er reduction techniques studied. Typically, reductions by this technique could be done in a few minutes. reductions to the ferrous state duration. Complete The sodium were also fairly short in reduction did not occur reduction. After the temperature, vaporization of the sodium and reduction oc curred quickly. hours. Samples were heated reduced in hydrogen The reached the The reduction by hydrogens long experiments. higher and zeolite had with sodium samples then had to room temperature. faster and could 400°C and twenty four be cooled back down to The microwave discharge reductions were be done at room reductions could have of the metals. were fairly up to from four to correct temperature. had an effect on The long the particle size The migration of iron to the surface of the catalyst could proceed slowly, but since the reduction time is long, most of the iron migrates during reduction. Perhaps reduction of the iron species slow but as the iron migrated in the pores was to the surface of the cata lyst, where the hydrogen concentration was greater, reduc tion occurred. tures or the It is not known whether the high tempera long reduction time caused the sintering of the iron particles. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 188 H.4 COMPARISON OF PARTICLE SIZE This was a very important area in this research. of the goals of this research cles that were small cages of zeolites. One was to produce metal parti enough to fit into Therefore, the the pores and particle size of the metal is very important in these studies. The microwave discharge reduction, was done at room temperature, particles; carbonyl zeolites The The reduction by hydrogen of iron prepared particles These particles were metal was zeolite. prepared the smallest metal the only metal particles small enough to fit in the pores of a zeolite. stroms. probably because it probably on Hydrogen samples prepared of 70 to 100 Ang larger than zeolite pores. the external reduction of surface of the bimetallic metal particles of 50 to the zeolite 80 Angstroms. These particles also were too large to fit in the pores of zeolites. The metal was probably on the zeolite in this case, too. particles Initially, similar in size outside of the The sodium reductions prepared to some iron was in the all of these preparation methods. the hydrogen reductions. cages of the zeolites in In all cases except for the reduction by microwave discharge, the iron metal was on the outside surface of the zeolite after the reduction. At some point, the iron migrated to the surface. probably due to the high temperatures employed. This was This mi- Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 189 gration could have occurred at tion. One possibility migrated to reached the the is that the metal surface before surface it were formed. two points in the prepara complex or ion reduction. was reduced After and large Another possibility is particles that the complex or ion was reduced in the zeolite to the surface and formed large particles.At high temp eratures, and atoms ions Perhaps both of cage and are very it then it migrated mobile in these processes occurred to zeolites. some extent. The microwave discharge experiment was unique in preparing reduced metal cages. Table particles 20 this research. percent reduction that remained the zeolite compares the reduction methods used in It contains lists of the metal and in of the particle sizes, the time needed for each method. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 190 TABLE 20 Comparison of Reduction Methods Method Microwave Hydrogen Bimetallic Sodium Particle Size <20 70-100 50-80 large % Reduction 100 100 100a 0 Particle size in Angstroms Time in hours a Totally reduced for some samples. Others Time short 2H H 80% reduced. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 191 4.4.1 Mechanisms of Reduction of Metal Complexes in Zeolites The method of reduction by microwaves involves the pro duction of a plasma state plex. This plasma is since microwaves alone which decomposes the metal com very important did not reduce the shown by experiments with no reduction complexes, argon gas present. microwave powers (100 Watts), posed and the metal complex The plasma is to the as At high the zeolite support decom formed large metal particles. the actual reducing agent in the method of reduction by microwaves. The plasma is a highly energetic state ionized argon species and electrons. ic state usually emits light. compose the metal complex consisting of This highly energet The argon plasma could de by several different processes. The argon plasma could penetrate the zeolite and decompose the metal complex in the pores. occurs, This penetration, if it is not too deep since the samples must be agitated to expose fresh zeolite to the plasma in pose all of the metal complex. of penetration arise Limitations in the degree from the fact that collision the argon plasma would lose its wall. The size of the argon ion also limits the degree of penetration. energy upon order to decom Miller and coworkers 191 with the zeolite have noted that ar gon species can be an 80 times bigger the ground state ar gon atom. These large argon ions would not fit into the Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 92 pores of a zeolite to decompose the metal complex. Pene tration of the electrons in the plasma into the zeolite is possible but the energy of the electron is to its small mass. Argon is probably the species in the plasma that causes the reduction the metal cess. the zeolite, since metal. the Reduction of be a surface pro diffuse to the surface of the experiments were done pressures(0.3 torr). face, to occur. complex could alternatively The metal complex could much less due at reduced Once the complex reaches argon plasma would the sur reduce the complex to the The small metal particles could then diffuse back into the zeolite pores. The reduction could also be a vapor state process. metal complexes are The volatile species and could be vapor ized under these reduced atmosphere conditions. The argon plasma would decompose the complex in the vapor state pro ducing the metal. The metal particles could then condense into the pores of the zeolite. close to the This vapor state could be surface of the zeolite. The zeolite might promote the vaporization of the complex. The size of the argon ion in the plasma makes the pene tration process questionable. vapor state reduction are production of metal. The surface reduction and both possible The absence duction causes the metal particles routes for the of heat during the re to remain small. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. For 193 this reason, the metal particles, by whatever process they are formed, are probably located in the pores and cages of the zeolites. Heat could be generated by of the argon ions with the microwaves or collision the zeolite. Vaporization of the complex could be promoted by this heat. This vaporization may be a necessary step before any postulated mechanism of argon-metal interaction could take place. Cooling of the sample by liquid nitrogen during microwave treatment could explore this concept. 1}.5 COMPARISON TO ZEOLITE CATALYSTS PREPARED BY OTHERS Table 21 contains a comparison of our results with some of the results of Stencel and coworkers similar 73 studies in the literature. prepared cobalt catalysts from the impregnation of metal nitrate solutions. The samples were reduced at 350°C in hydrogen for 24 hours. The catalysts 70 prepared by Stencel and coworkers 63$ pentane and formed 24? methane and hydrocarbons larger found that cobalt on ZSM-5 than pentane. We formed mostly methane and ethgo ane. Ozin zeolite Y by lysts and coworkers prepared metal atom vaporization. formed mostly butenes whereas iron and The cobalt on cobalt cata the iron formed methane and butenes as shown in Table 21. on Y catalyst formed mostly methane and ethane. catalysts Our iron Our cata Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. lysts formed similar products to *70 workers those of Stencel and co- QQ and Ozin and coworkers carbon products are smaller. ple preparations except that our hydro Perhaps differences in sam has influenced the samples. 73 lysts of Stencel and coworkers J The cata- could have cobalt on the outside of the zeolite because of the high reduction temp eratures. Perhaps the particle sizes of the metal in the catalysts of Ozin samples. and coworkers fin are different than our The effect of the zeolite cage on the hydrocar bons produced is more evident in our samples than in these other cases. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 195 TABLE Comparison of Catalyst Metal Support Coa Coa Coa Co Coc Fea Fec X ZSM-5 A ZSM-5 Y Y Y With Literature ci C2 C2T C3 C31 C4 0 35.1 100 24.4 25 50 19 19.5 43.9 0 2.7 0 50 - 22.0 1 .8 0 0 0 0 2 0 19.3 0 2.7 0 - 58.5 0 0 0.8 5 0 9 0 0 0 5.4 70 0 47 a Our results for microwave reduced samples b From Stencel and coworkers c From Ozin and coworkers Fe is sample III C1 - methane C2 - ethane C 2 ’ - ethylene C3 - propane C 3 ’ ~ propylene C4 - butane and butenes Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Chapter V CONCLUSIONS 5.1 INFORMATION GAINED This research shows small particles that it of iron is on various possible to supports. prepare It also shows that these samples are selective Fischer-Tropsch ca talysts. The size of the hydrocarbon produced from CO can be predetermined pore size. by choosing a Small zeolite with the correct metal particles of cobalt and iron on zeolites are ferromagnetic species and give characteristic ferromagnetic resonance spectra. These highly reactive and are pyrophoric in air. cobalt particles can be stabilized such as nitrogen or in vacuum The necessary lines and inert conditions for This technique, however, are Small iron and in an inert atmosphere for long periods preparation such atmosphere glove boxes make dures not easily transferable particles of time. as vacuum these proce to industrial applications. is novel and surely will find ap plication in other areas besides catalysis. - 196 - Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 197 5.2 FUTURE EXPERIMENTS 5.2.1 Catalytic Studies Important through some values information about these systems further catalytic studies. for iron and cobalt •on silica higher than on the zeolites. The can be g apparent and alumina were A comparison of the catalyt ic results of the metals on the zeolites versus silica and alumina might shed the supports. some light on the differences between Catalytic studies should show the influence of zeolite cages on the catalysts. Another experiment involves the use of microwaves in stead of heat as an activator in the Fischer-Tropsch reac tion. Rather than heat the catalysts to 250°C in a stain less steel reactor at one atmosphere of pressure, perhaps the reactions could be run at room temperature on a vacuum line in a quartz reactor. the activation energy. The microwaves could provide The products could be trapped and analyzed by gas chromatography after the reaction. 5.2.2 Characterization Studies The unknowns in the catalysis studies of the iron zeol ites prepared by to be identified. the reduction by microwaves method need Gas chromatography with mass spectros copy detection should help identify the unknown compounds. The size of the products as well as the functional groups attached will give some information about the reaction. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 198 The homogeneity couple of ways. of the samples If enough iron were present, «O Electron Mb'ssbauer the samples. could be studied Spectroscopy a in a Conversion oc ’ could be done on By varying the energy of the gamma rays that are analyzed, the depth of penetration or a depth profil ing experiment could be done. of the iron In this way, the variation concentration with sample depth could be ob served. Also, surface versus bulk metal concentration could be studied. Surface concentrations electron microscopy or Auger tration values could be could be obtained spectroscopy. obtained by Bulk concen by atomic absorption spectroscopy. Mossbauer studies would be possible of the microwave discharge if more iron could be deposited on the zeolite or a stronger source could be used. of 57 samples Also, the use Fe instead of common iron would give a stronger Moss bauer signal. Low temperature studies might also provide useful informa' 4on. 5.2.3 New Preparations Several new preparations are suggested by of this research. how samples The of iron and the results bimetallic zeolite studies showed either cobalt or duced catalysts that do not ruthenium pro^- carbide and do not apparently Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 99 deactivate. lyst, A cobalt-iron or ruthenium-iron zeolite cata perhaps prepared from carbonyls of the metals or even a mixed metal carbonyl cluster, could form such a ca talyst . The success of the reduction by microwaves of ferrocene experiment opens samples. a wide range of dation state. already in the zero oxi Iron ions can be reduced to the metal. reduction by microwaves of iron dicyclooctatetrene might give so that small metal particles some informa iron on the outside of a This molecule is too large to fit in a zeolite could possibly be formed on the outside surface of the zeolite. Other carbonyl spec ies could be studied such as R u ^ C C O ) ^ or W(C0)g. tion of cobaltocene The a large organometallic complex tion in the catalytic studies of zeolite. new The starting material does not have to be a car bonyl species where the metal is such as possibilities for to cobalt metal would Reduc be interesting to study the similarities with the cobalt catalysts formed from cobalt carbonyl. num would be Reduction of some complex of plati interesting since platinum is a catalyst in various reactions. The failure of the sodium that needs work. reductions is Experiments with another area careful pH control to 2+ stabilize Fe might produce and careful dehydration metallic species. of the supports Perhaps reactions in a Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 200 closed system where the entire reactor is in the oven might be successful. Microwave treatment of lead to the aluminoferrisilicates might further reduction past non-framework iron the ferrous might be reduced to state. The metallic species. Also microwave treatment of the bimetallic zeolite samples that reduced completely might form metallic iron. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. R E FE R E N C E S 1. Muetterties, E. L. Chem. E n g . News 1982, 2 8 - 4 1 . 2. Lauher, J. W. 5315. J. _Am. Chem. S o c . 1978, 100, 5305 - 3. Lauher, J. W. 2607. J.* AS!’ Chem. S o c . 1978, 101 , 2604 - 4. Muetterties, E. L. Chem. Rev. 1979, 79, 91. 5. Dixon, J. K . ; Longfield, J. E. in "Catalysis” , Vol 7; Emmett, P. H., Ed.; Reinhold: New York, 1960; pp 281 - 345. 6. Breck, D. W. 7. Boles, J. R . ; Flanigen, E. M . ; Gude, A. J. 3d; Hay, R. L . ; Mumpton, F. A . ; Surdam, R. C. "Mineralogy and Geology of Natural Zeolites"; Vol. 4, Southern Printing Company: Blacksburg, Virginia, 1977. 8. Breck, D. 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Kostapapas, A.; Zhang, Z . ; Suib, S. L . ; unpublished results. R eproduced with perm ission o f the copyright owner. F urther reproduction prohibited w itho ut perm ission. 213 VITA The author was born in Pittsburgh, Pennsylvania on Feb. 3> 1957 to Mr. and Mrs. his elementary Howard T. school and McMahon. high school He received education in Chartiers Valley school district in Bridgeville, vania. He graduated from Chartiers Valley the Pennsyl Senior High School in June 1975. His undergraduate degree was received from Geneva Col lege in Beaver Falls, Pennsylvania. lor of Science in Chemistry 1979. Presently, He received a Bache with Research Honors in May he is attending the University of Con necticut and will receive his Doctor of Philosophy in In organic Chemistry in March 1985. The author is a member of American Chemical Society. Phi Lambda Upsilon He and the has accepted the position of staff chemist at Union Carbide Corporation, Linde Divi sion, in Tonawanda, New York beginning in March 1985. R eproduced with perm ission o f the copyright owner. F urther reproduction prohibited w itho ut perm ission.