Nickel nanoparticles supported on silica were prepared by hydrazine reduction in aqueous medium. The obtained solids were characterized by X-ray diffraction (XRD), Transmission Electronic Microscopy (TEM), Electron Diffraction (ED), hydrogen chemisorption, and Temperature Programmed Desorption of hydrogen (H 2 -TPD). The catalytic properties were evaluated for benzene hydrogenation in the temperature range 75-230°C. XRD patterns reveal presence of the metallic nickel particles with fcc structure. Metal dispersion and hydrogen storage increase with decreasing metal particle size. The H 2 -TPD profiles exhibit two domains, one due to desorption of hydrogen from Ni metal and another due to spillover from metal to the support. The catalytic activity strongly depends on the metal loading. It increases with decreasing metal loading. This is attributed to metal surface area, which also increases with decreasing metal loading. Kinetic studies of benzene hydrogenation on the Ni catalysts showed that the benzene partial order is around -2. This significant negative value is ascribed to a strong adsorption of benzene on the catalyst surface.

Non conventional nickel (1%) and nickel (1%)-copper (0.2-0.75%) catalysts supported on silica, prepared by aqueous hydrazine reduction of nickel acetate at 70 degrees C, were studied in acetylene hydrogenation, mainly at 60 degrees C. The obtained results show that the metal dispersion decreases whereas the conversion passes through a maximum with increasing copper content. The reaction produces ethylene, benzene, ethane, n-butane, small amounts of higher hydrocarbons and a paraffinic product. Ethylene and benzene are rather low temperature products (below 80 degrees C) whereas the saturated hydrocarbons, mainly ethane, are rather formed at higher temperature. The presence of water in the feed gas changed the catalyst performances. The carbonaceous deposit during acetylene hydrogenation was studied by means of temperature programmed surface reaction (TPSR). Analysis of the results obtained showed that the changes observed in conversion/selectivity may be correlated with changes in Ni-Cu interactions, chemisorption equilibria or/and coke deposit. A comparative study of classical/non classical Ni/SiO2 catalysts is reported.

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