University of Illinois Urbana-Champaign

Synthesis of Platinum Dirhenium Dodecacarbonyl and Its Use as a Catalyst Precursor (Bimetallic, Rhenium, Heterogeneous)

Urbancic, Michael Anthony

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https://hdl.handle.net/2142/70241

Description

Title
Synthesis of Platinum Dirhenium Dodecacarbonyl and Its Use as a Catalyst Precursor (Bimetallic, Rhenium, Heterogeneous)
Author(s)
Urbancic, Michael Anthony
Issue Date
1984
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
Abstract
  • The use of a mixed-metal compound as a precursor to oxide-supported bimetallic catalysts offers the potential to control the composition of the resulting bimetallic particles. The reaction of HM(CO)(,5) (M = Re,Mn) with Me(,2)Pt(COD) (COD = 1,5-cyclooctadiene) in the presence of CO leads to the formation of the heterobimetallic compounds Re(,2)Pt(CO)(,12) and Mn(,2)Pt(CO)(,12) in high yield. HM(CO)(,5) can be readily prepared and isolated in (TURN)85% yield by the reaction of M(CO)(,5)Br with Zn dust and H(,3)PO(,4) in tetraglyme, followed by vacuum distillation. A single-crystal x-ray diffraction analysis of Re(,2)Pt(CO)(,12) shows that the molecule ideally possesses D(,2h) symmetry with octahedral coordination about each rhenium atom and square planar (trans) geometry about the platinum atom.
  • The Re(,2)Pt(CO)(,12) cluster has been supported on activated (gamma)-alumina and decomposed by temperature programmed heating in flowing H(,2). The decomposition profile shows that methane formation occurs at a significantly lower temperature than for a rhenium-only catalyst prepared from Re(,2)(CO)(,10).
  • The reduced catalysts derived from Re(,2)Pt(CO)(,12) have been characterized by H(,2) and CO chemisorption measurements, temperature programmed decomposition of adsorbed CO, as well as by the following catalytic reactions: CO methanation, propylene metathesis, and ethane or n-butane hydrogenolysis. Catalysts prepared from conventional precursors {(NH(,3))(,2)Pt(NO(,2))(,2) + NH(,4)ReO(,4)} have nearly identical metal dispersions as indicated by the chemisorption measurements. Nevertheless, the two catalysts show significant differences in catalytic behavior. For example, the cluster-derived catalysts exhibit higher activities ((TURN)threefold at 225(DEGREES)C) and higher apparent activation energies ((TURN)6 kcal/mole) for the hydrogenolysis reactions. Treatment of the reduced cluster-derived catalyst in air at 500(DEGREES)C followed by a second H(,2) reduction changes the catalyst in such a way that its catalytic properties are nearly identical to those of a conventionally-prepared catalyst. Taken altogether, the catalytic results are consistent with the presence of bimetallic particles in the cluster-derived catalyst, while segregation of the individual metals presumably occurs under oxidizing conditions.
Graduation Semester
1984
Type of Resource
text
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http://hdl.handle.net/2142/70241

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