Aggregation Mechanisms of Silica Particles in the Sol–Gel Synthesis of Promoted Silver Catalysts

Abstract

As found using in situ small-angle X-ray scattering (SAXS), a porous structure consisting of compact particles with sizes from 2 to 8 nm was formed as a result of the sol–gel synthesis of silicate, silicate–phosphate, and silicate–phosphate–silver gels from tetraethoxysilane. It was established that the aggregation of silica particles in the presence of nitric acid proceeds according to a coalescence mechanism. The presence of phosphoric acid in the system changes the mechanism of aggregation for Ostwald ripening. The introduction of silver nitrate into the system does not significantly affect the size of silica particles and the mechanism of their aggregation.