SILICA PILLARED METAL(IV) PHOSPHATE MATERIALS AS SUPPORTS FOR NICKEL-CATALYSTS

Two silica pillared phosphate materials containing different amounts o f silica have been used as supports to prepare, by impregnation, two s eries of metallic nickel catalysts (8, 10 and 15% loading). Thermal pr ogrammed reduction curves of nickel show two peaks at ca. 690 and 838 K denoting two different sites for Ni2+ ions assigned to the external and inner surface, respectively. These high reduction temperatures ind icate high dispersion and strong interactions with the supports. XPS a nalyses show that the reduction degree at 873 K (2 h) ranges between 2 2.5 and 30%. The metal dispersion and particle size were calculated fr om hydrogen adsorption isotherms at 298 K. These nickel catalysts are active in the hydrogenation of benzene (at 443 K). In both series of c atalysts no correlation between activities and metal dispersion was fo und, and turnover frequencies indicate an apparent structure sensitivi ty of the reaction, likely to be due to the presence of superficial un reduced nickel ions. TEM micrographs reveal that deactivation of catal yst occurs by formation of coke and filaments of carbon separating the nickel particles from the pillared materials.