PREPARATION OF NICKEL-TUNGSTATE CATALYSTS BY A NOVEL IMPREGNATION METHOD

Nickel-tungstate/gamma-alumina (NiW) catalysts were prepared by an inc ipient wetness impregnation method using citric acid as a complexing a gent. Citric acid has been used by our research group in preparing cob alt-molybdate and nickel-molybdate catalysts. The extended X-ray absor ption fine structure (EXAFS) data of the impregnating solutions indica ted that citric acid contributes to the formation of polytungstate ani ons that are smaller than the dodecarungstate ions formed when convent ional ammoniacal solutions are used. Sulfided NiW catalysts prepared b y using citric acid showed higher hydrogenation activity and hydrogena tion selectivity than NiW catalysts prepared using the conventional am moniacal solutions.