The Catalytic Behavior of Supported Ruthenium Cluster Compounds

Payne, Virgil Lynn

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Description

Title

The Catalytic Behavior of Supported Ruthenium Cluster Compounds

Author(s)

Payne, Virgil Lynn

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

• The suggestion that metal cluster compounds may serve as models for chemisorption on metal surfaces has led to their use as precursors for catalytically active species with well-defined structures. Previous research {1-3} using supported metal cluster carbonyl compounds suggests that under comparatively mild thermal conditions (< 200(DEGREES)C), CO may be reversibly dissociated from the cluster with no apparent loss of structural integrity.
• The present research concentrates on the preparation, catalytic behavior and characterization of supported metal particles derived from the cluster compounds Ru(,3) (CO)(,12) and Ru(,6)C (CO)(,14)C(,7)H(,8). These clusters were dispersed in very low concentration on high surface area alumina and silica and low area titania in an effort to produce isolated triplets, quartets and sextets of ruthenium atoms.
• Using the hydrogenolysis/dehydrogenation of n-butane as a diagnostic tool, it was observed that the catalytic behavior depends on the particular cluster as well as the pretreatment conditions and the support. While the Ru(,3)- and Ru(,4)-derived catalysts were similar with respect to selectivity towards the formation of methane, they differed greatly in comparison with the Ru(,6)-derived catalysts, which produced almost twice as much methane under similar conditions.
• There were no dramatic differences between the activities of the supported clusters, although catalysts derived from the traditional impregnation of supports with RuCl(,3) were nearly twice as active as the cluster-derived catalysts. Silica-supported catalysts were generally more active than alumina- or titania-supported catalysts.
• Physical characterization of the catalysts using hydrogen and carbon monoxide chemisorption revealed an uptake of less than 0.2 hydrogen atoms per ruthenium atom, indicative of a poorly dispersed catalyst. However, the samples exhibited an average CO uptake of one molecule per ruthenium atom. Since no large ruthenium particles could be observed using electron microscopy, this behavior could be attributed to metal-support interactions, as suggested by Bell {4} and Bassett and coworkers {5,6}.
• In conclusion, the evidence gathered using the ruthenium cluster compounds as precursors for supported metal particles suggests that decarbonylation and activation of the compounds gives rise to catalytically active species which interact strongly with the support, perhaps leading to oxidation of the metal. The observed product distributions suggest an increase in the extent of cracking of the butane molecule as the nuclearity of the initial cluster compound increases. This further suggests some retention of structure of the original cluster, even under severe catalytic conditions.
• References
• {1} A. K. Smith, et al., Inorg. Chem., 18, 3104 (1979). {2} J. Lieto, J. J. Rafalko, and B. C. Gates, J. Cat., 62, 149 {3} Z. Otero-Schipper, J. Lieto, and B. C. Gates, J. Cat., 63, 175 (1980). {4} A. T. Bell, et al., Abst. 179th A. C. S. Nat. Meeting, Colloid & Surf. Sci. Division, no. 36 {5} J. M. Basset, et al., J. Chem. Soc. Chem. Comm., p. 569 (1980). {6} J. M. Basset, et al., J. Organometal. Chem., 192, C31 (1980).

Graduation Semester

1981

Type of Resource

text

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