Properties of Bimetallic Catalysts Prepared From Alumina Supported Mixed Metal Catalysts
Hardwick, Steven John
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https://hdl.handle.net/2142/67262
Description
Title
Properties of Bimetallic Catalysts Prepared From Alumina Supported Mixed Metal Catalysts
Author(s)
Hardwick, Steven John
Issue Date
1981
Department of Study
Chemistry
Discipline
Chemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Inorganic
Language
eng
Abstract
Supported bimetallic catalysts represent an important class of commercial catalysts. Despite intensive study, a great deal remains to be learned about these systems. One difficulty associated with the characterization of supported metal catalysts is the variability of sites. Classically prepared bimetallic catalysts usually contain metal sites of varying size and stoichiometry. The decarbonylation of mixed metal carbonyl clusters has been suggested as a method of preparing highly dispersed crystallites of well defined size and stoichiometry.
Hydrogenation of ethene was investigated over a series of alumina supported iron-ruthenium mixed metal carbonyls. The observed order of activity was:
Ru(,3)(CO)(,12) was approximately two orders of magnitude more active than Fe(,3)(CO)(,12). The catalytic activities of the mixed metal carbonyls were approximately what one would expect from additive behavior of Ru(,3)(CO)(,12) and Fe(,3)(CO)(,12).
A series of complexes of the general formula CpMOs(,3)(CO)(,12)H, where M = Mo or W, supported on alumina were also investigated. During activation in hydrogen most of the carbonyl ligands were hydrogenated to form methane. RTD of alumina supported Os(,3)(CO)(,12) and CpMOs(,3)(CO)(,12)H complexes showed similar decarbonylation behavior for all three complexes. CO/Os ratios of 1-1.2 indicated that the resulting metal particles were highly dispersed. Studies employing catalytic methanation of carbon monoxide showed that all three clusters had similar activity, selectivity and activation energies, indicating that osmium was solely responsible for the catalytic behavior of these supported metal catalysts.
Very small supported bimetallic crystallites were prepared on alumina using precursors of the general formula Cp(,n)W(,n)Ir(,4-n)(CO)(,12-n), where n = 0-2. Hydrogen and carbon monoxide chemisorption indicated that the catalysts were very highly dispersed; probably containing metal particles less than 10 A in size. Activation in hydrogen resulted in the hydrogenation of most of the carbonyl ligands to methane. The persistance of a tungsten-iridium interaction was indicated by differences in reactive thermal desorption curves observed over this series of catalysts. Differences observed in the activity, selectivity and activation energies for n-butane hydrogenolysis over the tungsten-iridium catalysts relative to pure iridium catalysts also supported the suggestion of continued metal-metal interactions on activation.
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