Ivashchenko N. Formation of palladium and platinum nanoparticles on the surface of chemically modified silicas

The thesis is devoted to synthesis and studies of supported palladium and platinum nanoparticles by application of the chemically modified silicas with grafted silicon hydride groups. Contact of palladium nitrate and hexachloroplatinic acid water solutions with the silica surface modified with silicon hydride groups was shown to result in reduction of palladium and platinum ions to the metallic state. Variation of metal content in the nanocomposites allows one to regulate the size of palladium and platinum nanoparticles within the certain limits. The possibility of palladium nanoparticles size regulation by using ordered porous silica matrices with pores larger than 4 nm was demonstrated. Thus, the application of triethoxysilane modified SBA-15 silica (dpores=6.2 nm), even with metal content 1.0 wt. % allows to obtain uniform (about 5 nm) spherical palladium nanoparticles incorporated into the pore channels of the porous matrix. It was demonstrated that the formation of a hydrophobic environment around silicon hydride groups grafted to the silica surface, particularly by using hexamethyldisilazane and diizopropylchlorosilane, significantly reduces aggregation of formed particles. Moreover it ensures the formation of palladium nanoparticles with quite narrow size distribution (3-4 nm). The catalytic activity of palladium-containing silicas in reaction of carbon monoxide and methane oxidation was studied.