Hydrogenation of citral and cinnamaldehyde over bimetallic Ru-Me/Al2O3 catalysts

Hydrogenations of citral and cinnamaldehyde have been investigated over Ru-Me/Al2O3 (Me = Ge, Sn, Pb). Two series of catalysts have been prepared by using the controlled surface reaction (CSR) technique (RuEC series) and the more conventional co-impregnation method (RuNI series). Addition of Ge increases the catalytic activity on the RuEC series whereas no modifications are found on the samples prepared by co-impregnation. The selectivity to unsaturated alcohols is not influenced by the presence of Ge. Addition of tin increases both the activity and the selectivity regardless of the preparation method. The presence of lead does not modify the selectivity and a slight decrease in the catalytic activity is observed on the sample of the RuNI series. On the basis of the characterization data available on the investigated catalysts, it is suggested that Ru and Ge interacts when the samples are obtained through the CSR technique, Such an interaction increases the catalytic activity likely through a decrease of the strength of adsorption of one of the reaction components. The positive effect of tin on the catalytic activity and selectivity is discussed.