High-active nickel catalyst of NiB/SiO2 for citral hydrogenation at low temperature

A high-active supported nickel catalyst of NiB/SiO2 was obtained by impregnation-chemical reduction for liquid-phase hydrogenation. The precursor salt of nickel was mounted on SiO2 by impregnating, drying and calcination at an appropriate temperature without being decomposed, and then reduced with aqueous NaBH4 solution. The factors that governed the preparation of NiB/SiO2 catalysts were examined by the hydrogenation of butyraldehyde. The NiB/SiO2 catalysts were characterized as an ultrafine and amorphous structure, which were much more active than NiB and Ni/SiO2, a conventional supported nickel catalyst reduced by H2. The optimal catalyst of 5% NiB/SiO2 was used to hydrogenate citral to citronellal and citronellol, which was about 14 times as active as NiB, but less selective than NiB. Nevertheless, the reaction could be performed at room temperature to promote the selectivity. A high yield of citronellal/citronellol of about 98% and a yield of citronellal of about 84% over 5% NiB/SiO2 were obtained at a low temperature of 30 deg C.