Studies on nickel oxide mixed catalysts. Part 12.—Characterization of NiO/Al2O3–SiO2 catalysts

Abstract

NiO/Al₂O₃–SiO₂ catalysts containing 5 mol% NiO and various amounts of alumina have been prepared by precipitation. Nitrogen adsorption–desorption isotherms on both the calcined samples and the corresponding Al₂O₃–SiO₂ precursors have been measured. Surface areas S_B.E.T. and S_t have been calculated and the pore structure analysed. The composition and electronic structure of the surface have been characterized by ESCA and the state of the nickel component also by magnetic susceptibility and reflectance spectroscopy studies.

The results indicate that reactions between the components take place in the course of the preparation, forming X-ray amorphous nickel layer silicates and nickel alumino layer silicates, which influence the textural properties of the NiO/Al₂O₃–SiO₂ catalysts. In general, a decrease in the specific surface areas and the total pore volumes has been found. The presence of micro- and meso-pores has been observed in samples with low alumina contents.

Thermal activation of the catalysts above 700 K leads to the formation of coordinatively unsaturated nickel ions and small amounts of nickel oxide, depending on the alumina content.