Completely selective hydrogenation of trans-cinnamaldehyde to cinnamyl alcohol promoted by a Ru–Pt bimetallic catalyst supported on MCM-48 in supercritical carbon dioxide

Abstract

Supercritical carbon dioxide (scCO₂) is a unique reaction medium for the selective hydrogenation of cinnamaldehyde using a well-defined Ru–Pt bimetallic catalyst supported on MCM-48. The reaction is completely selective to the unsaturated alcohol in supercritical carbon dioxide. The selectivity to the desired unsaturated alcohol shows a significant pressure dependence. By varying the pressure at the constant reaction temperature of 323 K, we are able to optimize the selectivity of cinnamyl alcohol to 100%. This is a particularly dramatic enhancement compared to that in organic solvents and under solventless conditions, where Ru–Pt bimetallic catalyst produces cinnamyl alcohol along with hydrocinnamaldehyde and 3-phenylpropanol. More importantly, the excellent physicochemical properties of the scCO₂ medium provide a significant influence on the selectivity, which goes beyond that of simple solvent replacement only.