The Photocatalytic Reduction of CO2 with H2O on Titanium Oxide Catalysts

Abstract

UV irradiation of active titanium oxide catalysts in the presence of CO2 and H2O at 275 K led to the photocatalytic reduction of CO2. The characteristic features of the photocatalytic reduction of CO2 with H2O on various types of active titanium oxide catalysts were investigated by in situ photoluminescence, UV-Vis, XAFS, ESR, FT-IR and XPS spectroscopic techniques. The reactions on TiO2 powders and Ti/Si binary oxides prepared by the sol-gel method produced methane as the major product while, on the highly dispersed titanium oxide anchored on a porous glass and zeolites, the formations of CH4, CH3OH, C2-compounds, and CO were observed as the major products. The yields of the photocatalytic reactions strongly depended on the type of catalysts, the value of CO2/H2O, and the reaction temperature. In situ spectroscopic studies of the system indicated that the photocatalytic reduction of CO2 with H2O is linked to a much higher reactivity of the charge transfer excited state, i.e., (Ti3+-O-)3∗ of the tetrahedral coordinated titanium oxides species formed on the surface. Based on the detection of reaction intermediate species such as Ti3+, H atoms, and C radicals, the reaction mechanism for the photocatalytic reduction of CO2 with H2O has been proposed on a molecular scale. © 1995, The Japan Petroleum Institute. All rights reserved.