Gamma-Al2O3-Supported Re-Pt Cluster Catalyst Prepared from [Re2Pt(CO)12]: Characterization by Extended X-Ray Absorption Fine Structure Spectroscopy and Catalysis of Methylcyclohexane Dehydrogenation.

Abstract

A model catalyst prepared from [Re2Pt(CO)12] supported on ç-Al2O3 was characterized by extended X-ray absorption fine structure (EXAFS) spectroscopy, and its stability in operation in a flow reactor was tested for the dehydrogenation of methylcyclohexane at 1 atm and 400 ¢XC. EXAFS data characterizing the unused catalyst measured at both the Re LIII and Pt LIII edges at liquid nitrogen temperature with the sample in the presence of H2 distinguish the Re-Pt from the Pt-Pt and Re-Re interactions. The EXAFS results form the basis of a simplified model of the supported bimetallic structures, consisting of Re4Pt2 entities, with oxophilic Re in a low positive oxidation state interacting strongly with the oxygen atoms of the ç-Al2O3 support and stabilizing the dispersion of the Pt atoms. The catalyst made from [Re2Pt(CO)12] was found to be more resistant to deactivation during catalytic dehydrogenation of methylcyclohexane than catalysts prepared conventionally from Re and Pt salt precursors. The catalyst prepared from [Re2Pt(CO)12] was more highly dispersed than the others, and its resistance to deactivation is attributed to the role of Re in stabilizing the dispersion of the Pt.