Structural and Catalytic Properties of Ni/SiO2 Prepared by Solution Exchange of Wet Silica Gel

Abstract

Structural formation of Ni/SiO2 in a solution exchange method, where Ni was supported on silica by exchanging the solution in wet silica gel derived from tetraethoxysilane under acidic conditions, and its catalytic property were investigated. In the preparation of Ni/SiO2, the dispersion of Ni is largely dominated by aggregation in drying, while mesopore structure in the silica support can be controlled to ∼4 nm by exchanging the solution with strong acids. When aqueous nickel nitrate solution is used in the solution exchange, large nickel nitrate crystals are formed within the gel matrix during drying. They decompose into aggregates of NiO crystallites, with sea–island distribution during calcination. On the other hand, the use of citric acid together with nickel nitrate in the solution exchange effectively inhibits the aggregation of Ni species in drying through the formation of nickel citrate, which barely crystalizes in drying. In calcination, the nickel citrates decompose into NiO particles, and their distribution in the silica matrix becomes homogeneous. Additionally, the use of citric acid and calcination in an inert atmosphere has another effect, decreasing the particle size of NiO and Ni. Consequently, we can prepare Ni/SiO2 catalyst with high Ni surface area at high Ni content, which shows superior catalytic activity in the hydrogenation of benzene.