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

A model catalyst prepared from [Re2Pt(CO)(12)] supported on gamma-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 degrees C. EXAFS data characterizing the unused catalyst measured at both the Re L-III and Pt L-III edges at liquid nitrogen temperature with the sample in the presence of H-2 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 gamma-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.