TEXTURE, STRUCTURE, SURFACE AND CATALYTIC PROPERTIES OF SILICA-GEL MODIFIED BY METHODS OF CHEMICAL MIXING .2. HYDROPHILIC, ACID, AND ELECTRON-ACCEPTOR PROPERTIES

The hydrophilic, acid, and electron-acceptor properties of SiO2 doped with Al3+, Ti4+, Zr4+, and Ce4+ cations were investigated. It was shown that doping of SiO2 is accompanied by a significant increase in adsorption of NH3 and especially H2O in comparison to pure SiO2, and incorporation of cations in the surface layer of SiO2 is accompanied by the formation of several adsorption sites, each of which adsorbs one molecule of NH3 or 2-3 molecules of H2O. The higher heats of adsorption of NH3 on the doped samples suggests that there are acid sites on their surface whose strength is close to the strength of the acid sites of zeolite. It was found that in addition to acid sites, electron-acceptor sites are also formed on the surface of doped SiO2, and their concentration is maximum on the surface of the samples doped with Ti4+ and Ce4+ cations.