Study of nickel catalysts supported on silica of low surface area and prepared by reduction of nickel acetate in aqueous hydrazine

Nickel metal nanoparticles supported on low surface area silica were prepared by reduction of nickel acetate with hydrazine in aqueous medium. The catalysts were characterized by atomic absorption, XRD, TEM, BET surface area, and H2 chemisorption and TPD. Their hydrogenating properties were evaluated in the gas-phase hydrogenation of benzene. It was found that gas-phase stability and surface properties of the supported nickel particles depended on the nature and temperature of pretreatment. Small nickel particles, in an oxidized or reduced state, were strongly resistant to reducing or oxidizing treatment, respectively. For H2-treated catalysts, H2 chemisorption and TPD results suggested the occurrence of hydrogen spillover between the metal nickel phase and the silica. For air and H2-treated catalysts, hydrogen spillover seemed to involve, in addition, the NiO phase. The activity of the catalysts in benzene hydrogenation also depended on the thermal pretreatment. Precalcined and then reduced catalysts exhibited higher TOFs than nonprecalcined catalysts, suggesting that the presence of the NiO phase may have influenced the hydrogenation process. A comparative study showed that a catalyst prepared by reduction of nickel acetate by hydrazine in aqueous medium stored more hydrogen and was more active in benzene hydrogenation than a conventional catalyst.