The Hydrogenation of Cinnamaldehyde Over Silica Supported Copper and Modified Copper Catalysts

A series of silica supported copper and modified copper catalysts has been prepared, characterised and used for the hydrogenation of cinnamaldehyde. Supported copper catalysts were doped with V, Pd or Ru to investigate their effects on the cataysts activity and selectivity. The catalysts were prepared by impregnation of preformed silica pellets with metal salts of the appropriate ions. The metal components of the catalysts were as follows:- Cu/SiO2 Cu/V/SiO2 Cu/V/Pd/SiO2 Cu/Pd/SiO2 Cu/Ru/SiO2 V/SiO2 The copper, palladium and ruthenium contents of the catalysts were varied. Grace and PQ silicas were used. These silicas were supplied by I.C.I. The catalysts were characterised using temperature programmed reduction (TPR) studies and the copper metal dispersions were calculated by following the decomposition of NgO over the reduced catalysts. Selected catalysts were also characterised by hot stage x-ray diffraction (XRD), transmission electron microscopy (TEM) and mercury porosimetry. TPR studies of copper oxide supported on Grace and PQ silica showed that the TPR profile could be drastically altered by varying 1. copper metal content 2. the silica support 3. the procedure for calcination of the precursors. The reduction temperature was found to increase with increasing copper metal content and extra high temperature peaks were sometimes observed. The reduction temperature of the TPR profiles was lowered and reduction took place over a narrower temperature range when the higher surface area Grace silica weis used as a support rather than PQ silica. Calcination of the imcalcined supported precursors in flowing air rather than in a muffle oven also resulted in a lowering of the reduction temperature. The silica supported CuO and V2O5 calcined catalyst precursor was found to reduce concomitantly at the temperature normally found for the supported CuO although supported V2O5 itself reduced at much higher temperatures. Generally addition of palladium to the supported copper oxide lowered the reduction temperature while a new low temperature reduction peak emerged when ruthenium was added to supported CuO. The copper metal dispersion was highest in the copper oxide on Grace silica catalysts. The V2O5 had no effect on the copper metal dispersion but the addition of palladium generally increased the dispersion. Increasing the content of ruthenium chloride in the catalyst precursor resulted in a decrease in the copper metal dispersion in the reduced catalyst. Dispersion was improved for copper by calcining the catalyst precursors in flowing air rather than in a muffle oven, and also by calcining at lower temperatures. Although in the hydrogenation of cinnamaldehyde, selective reduction of the carbon-carbon double bond was generally favoured, optimisation of the preparative variables resulted in the production of Cu/SiO2 catalysts which were selective for the production of cinnamyl alcohol from cinnamaldehyde. The rate of hydrogenation was found to be greater on the Grace supported copper than on its PQ counterpart. However, the Grace supported copper metal catalysts always selectively hydrogenated the carbon-carbon double bond in the cinnamaldehyde to form hydrocinnamaldehyde. The addition of palladiimi to the catalysts also increased the hydrogenation rate, forming mainly hydrocinnamaldehyde. Selectivity to cinnamyl alcohol was induced by adding RuClg to the supported copper catalyst precursor. Addition of V2O5 to the supported copper catalysts resulted in a loss of activity. Grenerally the catalysts which showed high activities were less selective for cinnamyl alcohol formation. These catalysts also were found to reduce at lower temperatures in the TPR profiles and have the higher copper metal dispersions. The variations in the hydrogenation properties of each of the catalysts was assigned to a combination of the following factors:- 1. the addition of an extra metal 2. the copper metal particle size 3. metal-support interactions. The results were interpreted in terms of a concerted mechanism in which phenyl propanol was formed by the successive hydrogenation of hydrocinnamaldehyde and cinnamyl alcohol