The selective hydrogenation of alpha,beta-unsaturated aldehyde was studied over cobalt borides. The effects of Fe, Cu, Sn, Mo and Th additions were examined for the hydrogenation of cinnamaldehyde. Fe and Sn did not promote the formation of unsaturated alcohol as expected. Molybdenum effectively promoted the overall rate and the yield of unsaturated alcohol. Thorium not only promoted the activity, but also slightly promoted the selectivity. The promotional effects of molybdenum and thorium were attributed to the affinity between carbonyl and promoter ions. This model is very similar to that proposed for their promotional effects on group VIII metals in CO hydrogenation. A lower reactant concentration, a higher pressure and temperature (in the range of 373-403 K) favored the formation of unsaturated alcohol. A protic solvent such as ethanol or isopropanol is preferable to an aprotic solvent for this reaction. The addition of an appropriate amount of water to ethanol increased the rate of reaction by 100%.
