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-Al2O 3 was characterized by extended X-ray absorption fine structure (EXAFS ) spectroscopy, and its stability in operation in a flow reactor was t ested for the dehydrogenation of methylcyclohexane at 1 atm and 400 de grees C. EXAFS data characterizing the unused catalyst measured at bot h 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 simplif ied model of the supported bimetallic structures, consisting of Re4Pt2 entities, with oxophilic Re in a low positive oxidation state interac ting strongly with the oxygen atoms of the gamma-Al2O3 support and sta bilizing the dispersion of the Pt atoms. The catalyst made from [Re2Pt (CO)(12)] was found to be more resistant to deactivation during cataly tic dehydrogenation of methylcyclohexane than catalysts prepared conve ntionally from Re and Pt salt precursors. The catalyst prepared from [ Re2Pt(CO)(12)] was more highly dispersed than the others, and its resi stance to deactivation is attributed to the role of Re in stabilizing the dispersion of the Pt.