Reaction mechanism of 2-propanol dehydrogenation with a carbon-supported Ru-Pt composite catalyst in the liquid phase

The liquid-phase dehydrogenation of (CH3)(2)CHOH, (CH3)(2)CHOD, and (CH3)(2)CDOH to yield acetone and molecular hydrogen was per-formed selectively under boiling and refluxing conditions by heating a suspended solution of a W C 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 82.4degreesC from (CH3)(2)CHOD and (CH3)(2)CDOH, 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)(2)CHOD.