Showing papers by "Donna G. Blackmond published in 1992"

Influence of alkali promoters in the selective hydrogenation of 3-methyl-2-butenal over ruthenium/silica catalysts

Abstract: The addition of potassium as a promoter to a Ru/SiO{sub 2} catalyst resulted in a striking shift in product selectivity in the hydrogenation of 3-methyl-2-butenal. The rate of hydrogenation of 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. 40 refs., 6 figs., 3 tabs.

Diffusion effects in the hydrogenation of 3-methyl crotonaldehyde over zeolite-supported Ru

Abstract: The activity and selectivity in gas-phase hydrogenation of the unsaturated aldehyde 3-methyl crotonaldehyde (UAL) over zeolite-supported Ru was found to depend markedly on the partial pressures of the two reactants in the gas phase, with the rate increasing as the ratio\(P_{UAL} /P_{H_2 }\) decreased. Anomalously low apparent activation energies were found compared to the same reaction over Ru/SiO2, and secondary reactions to produce the totally hydrogenated product occurred much more readily in the zeolite-supported Ru. These observations led to the suggestion that these reactions were under diffusion control.