INFLUENCE OF ALKALI PROMOTERS IN THE SELECTIVE HYDROGENATION OF 3-METHYL-2-BUTENAL OVER RU/SIO2 CATALYSTS

The addition of potassium as a promoter to a Ru/SiO2 catalyst resulted in a striking shift in product selectivity in the hydrogenation of 3-methyl-2-butenal. The rate of hydrogenation at the C=O bond to produce the unsaturated alcohol increased concomitant with a decrease in the rate of C=C hydrogenation. IR spectroscopy showed a strong perturbation of the C=O bond for the alkali-promoted catalyst, and volumetric chemisorption and TPD results suggested that the alkali species blocked adsorption at low-coordination Ru sites. These adsorption and reaction studies suggest that polarization of the adsorbed substrate at the C=O bond is responsible for the significant shift in product selectivity upon alkali promotion. This work combines spectroscopic tools with the use of the catalytic reaction itself as a probe of catalyst surface chemistry.