The influence of Si-modified TiO2 on the activity of Ag/TiO2 in CO oxidation

Nanocrystalline TiO2 and Si-modified TiO2 with Si/Ti ratios 0.01, 0.05, 0.1, and 0.3 were prepared by the solvothermal method and employed as the supports for Ag/TiO2 catalysts for CO oxidation reaction. The incorporation of Si into the TiO2 lattice in the form of Ti–O–Si as revealed by FT-IR results could inhibit the agglomeration of TiO2 crystallites, resulting in an increase of both surface area and metal dispersion. However, there existed an optimum content of Si/Ti at ca. 0.05–0.1 which resulted in an improved catalytic activity of Ag/TiO2 in CO oxidation. Based on the O2-temperature program desorption (O2-TPD) results, the catalysts with appropriate amounts of Si/Ti exhibited higher amount of O2 adsorption and much lower desorption temperature. It is suggested that the presence of Ti–O–Si promoted the formation of active oxygen species and increased the mobility of lattice oxygen so that the catalytic activity was enhanced. There was no improvement in CO oxidation activity of the Ag/TiO2 catalyst when the Si/Ti was further increased to 0.3 due probably to the formation of amorphous SiO2 instead of the Ti–O–Si bond.