High-loaded nickel-silica catalysts for hydrogenation, prepared by sol-gel Route: structure and catalytic behavior

Ni/SiO2 catalysts (from 50 to 95 wt.% of nickel) were prepared by the heterophase sol-gel method through impregnation of dispersed hydrated nickel oxide with commercial ethyl silicate-32. Impregnation of a porous metal precursor with alcoholic solution of the ethyl silicate followed by drying makes it condensed to form polysiloxane films directly on the precursor surface. The next steps of calcination and reduction lead to formation of a silica matrix with metal nanoparticles confined in its pores. Si-29 NMR, IR spectroscopy, differentiating dissolution, temperature-programmed reaction (TPR), X-ray powder diffraction (XRD) and transmission electron microscope (TEM) techniques were used for studies of the precursors and catalysts. It was shown that silicate species favoring formation of fine nickel particles under reduction were produced by interaction of hydrated NiO with ethyl silicate. As the silica content increased from 5 to 52%, the nickel particles decreased in size from 10 to 4 nm. The sol-gel catalysts were tested in the reaction of benzene hydrogenation to show that the nickel surface was not blocked by silica but exposed to reactants. As a result, the observed catalytic activity was higher than the activity of a number of commercial nickel catalysts. (C) 2002 Elsevier Science B.V. All rights reserved.