Ni/SiO 2 prepared by sol–gel process using citric acid

Abstract

A Ni/SiO 2 with high Ni content over 50 wt% in NiO form was prepared from a solution of TEOS, nickel nitrate and citric acid. The additive citric acid contributes both the formation of mesopores and increase in the Ni dispersion. The Ni/SiO 2 has large mesopores with size of 5–10 nm. The mesopores are formed by eliminating citric acid from the silica–Ni–citric acid composite with small shrinkage, i.e. the spaces occupied with citric acid in the composite directly turn to pores after elimination. Although large shrinkage in pores occurs when the composite is calcined in air, the calcination in an inert atmosphere is effective to suppress the shrinkage during calcination. In addition to the controlled large mesopores, high Ni dispersion is achieved in the Ni/SiO 2. Nickel citrate formed in the as-prepared silica–Ni–citric acid composite effectively suppresses the aggregation of Ni species during drying because of low crystallization ability of nickel citrate. Furthermore, the following calcination in an inert atmosphere has an additional effect to increase Ni dispersion. Thus prepared samples keep small Ni particle size even at high Ni content of ≈50 wt% after reduction at 500 °C, and show high Ni surface area over 30 m 2 g −1.