Synthesis and catalytic activity of porous blocked Ag/SiO2 composites in low-temperature carbon monoxide oxidation

The Ag/SiO₂ composites were synthesized based on porous blocked silica with a pore size of 30–50 nm and a specific surface area of 99 m²/g. Silver particles were introduced into the pores of the support by its impregnation with a solution of an ammonium complex of silver followed by reduction with hydrogen. The liquid-phase reduction of silver ions in pores was performed in the absence of stabilizing agents with the use of ethylene glycol (a polyol method) or formamide as a reducing agent. The methods used in the preparation of composites made it possible to vary the particle size of silver. The greatest size that is almost comparable with the pore size was achieved with the use of formamide. The catalytic activity of the Ag/SiO₂ composites was studied in the reaction of CO oxidation. It was found that the catalysts obtained upon the reduction of Ag⁺ ions by formamide exhibited considerable low-temperature activity. A necessary condition for the manifestation of low-temperature activity is redox treatment, in the course of which the particle size of silver considerably decreases.