Reaction Mechanism of 2-Propanol Dehydrogenation with a Carbon-Supported Ru-Pt Composite Catalyst in the Liquid Phase

The liquid-phase dehydrogenation of (CH3)2CHOH, (CH3)2CHOD, and (CH3)2CDOH to yield acetone and molecular hydrogen was performed selectively under boiling and refluxing conditions by heating a suspended solution of a carbon-supported ruthenium and platinum composite catalyst. The Ru-Pt/carbon composite catalyst gave kinetic isotope effects of 1.54 and 1.96 for dehydrogenation at 82.4 °C from (CH3)2CHOD and (CH3)2CDOH, respectively, which were contrasted to the corresponding magnitudes of 1.69 and 1.57 with a Ru/carbon catalyst and those of 1.13 and 1.81 with a Pt/carbon catalyst. The rate constants of dehydrogenation as a function of the H/D ratio in molecular hydrogen suggest that the step to form molecular hydrogen from surface hydrogen species was slow on the Ru catalyst, whereas the step to split the methine C-H bond was rather difficult for the Pt and Ru-Pt catalysts. Reflecting the facile dissociation at the hydroxy group on the catalyst surface, deuterium transfer from the hydroxy to the methyl groups of both acetone and 2-propanol proceeded tremendously for (CH3)2CHOD.