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Title:Synthesis of Platinum Dirhenium Dodecacarbonyl and Its Use as a Catalyst Precursor (Bimetallic, Rhenium, Heterogeneous)
Author(s):Urbancic, Michael Anthony
Department / Program:Chemistry
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(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.
Issue Date:1984
Description:216 p.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1984.
Other Identifier(s):(UMI)AAI8409844
Date Available in IDEALS:2014-12-15
Date Deposited:1984

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