Benzene hydrogenation over Ni–Cu/SiO2 catalysts prepared by aqueous hydrazine reduction

Non conventional nickel (1%) and nickel (1%)–copper (0.2%–0.75%) catalysts supported on silica have been prepared by aqueous hydrazine reduction of nickel acetate at 70 °C. They were characterized by TEM, H2-adsorption, H2-TPD and tested in the gas phase hydrogenation of benzene at atmospheric pressure in the temperature range 75 °C–230 °C. The obtained results show that nickel is in a whisker-like shape or as a film of low density for the Ni/SiO2 and Ni–Cu/SiO2 catalysts respectively. Copper is in the shape of facetted particles in the mono or bimetallic systems with a mean particle size varying from 25 to 100 nm. The presence of copper decreased the nickel phase dispersion as well as the conversion whereas it increased carbon deposit in benzene hydrogenation. The results obtained are ascribed to nickel phase shape changes and Ni–Cu interactions. A kinetic reaction mechanism model is proposed. The comparative study of a pair of classical/non-classical Ni/SiO2 catalysts showed much higher surface and catalytic properties of the hydrazine catalyst.