Selective hydrogenation of cinnamaldehyde over supported copper catalysts

The selective hydrogenation of cinnamaldehyde in the liquid phase has been studied using silica-supported catalysts. Selectivity to cinnamyl alcohol was found to be dependent on both the silica used and the way in which the catalyst had been prepared. The highest selectivity was achieved using a 13.7 wt% Cu/PQ-silica catalyst prepared by an impregnation route. This catalyst contained large copper crystallites and small amounts of Cu2O at the metal-support interface. Modification of the catalyst by doping with palladium resulted in an acceleration of the rate of reaction but a loss in selectivity. CuO/V2O5/PQ-silica formed a copper-vanadia bronze on reduction, but the rate of hydrogenation of cinnamaldehyde was much lower than for Cu/PQ-silica and the catalyst was not selective for cinnamyl alcohol. The hydrogenation of cinnamaldehyde over the supported copper catalysts proceeded on a modified surface formed from adsorbed hydrocinnamaldehyde. Cinnamaldehyde was hydrogenated to hydrocinnamaldehyde and, in some cases, also cinnamyl alcohol. Hydrocinnamaldehyde was then further hydrogenated to phenyl propanol. Selectivity to cinnamyl alcohol using the 13.7 wt% Cu/PQ silica catalyst remained high even at 80% conversion. (C) 1997 Academic Press.