Promotional effect of Au on reduction of Ni(II) to form Au–Ni alloy catalysts for hydrogenolysis of benzylic alcohols

Gold-nickel bimetallic catalysts were prepared from Au/NiO and Au(OH)3—Ni(OH)2—NiCO3 coprecipitates which showed exelent catalytic activities and selectivities for the hydrogenolysis of benzylic alcohols into alkylbenzene derivatives. •Au on NiO promoted Ni(II) reduction to produce active Au–Ni bimetallic catalysts.•Reduction of Au(OH)3–Ni(OH)2–NiCO3 coprecipitates with H2 produced Au–Ni alloys.•The Au–Ni alloy catalyzes hydrogenolysis of benzylic alcohols with high selectivity. Gold–nickel bimetallic catalysts were prepared from Au/NiO and Au(OH)3–Ni(OH)2–NiCO3 coprecipitates by treatment with hydrogen. Gold promoted the reduction of Ni(II) to Ni(0) at relatively low temperatures in the range of 100–150°C, which was confirmed by H2-TPR and in situ XAFS measurements, whereas NiO without Au was not fully reduced even at 300°C. The obtained catalysts were characterized by XRD, HAADF-STEM, XAFS, and 197Au Mössbauer, and these analyses revealed the formation of Au–Ni alloy components in the obtained catalysts. Au existed as Au nanoparticles together with Au–Ni alloy components in Au–Ni-1 prepared from Au/NiO by H2 treatment. When Au(OH)3–Ni(OH)2–NiCO3 was treated in a flow of H2 to produce Au–Ni-2, the formation of Au NPs was not clearly observed, thereby meaning that Au atoms were highly dispersed as a single atom and/or small clusters in the obtained catalysts. Moreover, most of the Au atoms were alloyed with Ni atoms for Au–Ni-2. The obtained Au–Ni-1 and Au–Ni-2 exhibited superior catalytic activities for the selective hydrogenolysis of benzylic alcohols into alkylbenzene derivatives in terms of reaction rates normalized by catalyst surface area. Accordingly, Au–Ni-1 and Au–Ni-2 recorded the reaction rates of 4.79 and 9.79mmolL−1h−1m−2, respectively. These values were greater than that obtained for Raney Ni (0.14mmolL−1h−1m−2). In addition, Au–Ni-2, which contains higher Au–Ni alloy content, showed greater reaction rates when compared to Au–Ni-1. Since Au/TiO2 showed poor catalytic activity for the hydrogenolysis, Au–Ni alloy enhanced the catalytic activities of Ni(0).