Photocatalytic reduction of CO2 with H2O on various titanium oxide catalysts

Abstract

Abstract UV irradiation of highly dispersed, anchored titanium oxide catalyst and finely powdered TiO2 catalysts in the presence of a mixture of CO2 and H2O led to the formation of (CH4 + CH3OH + CO) and CH4, respectively, into the gas phase at 275 K. The efficiency of these photoreactions depended strongly on the kind of catalyst, the ratio of CO2 to H2O, and the reaction temperature. In the case of highly dispersed titanium oxide catalysts, the charge transfer excited state, i.e. (Ti3+ O−)3* of the tetrahedral coordinated titanium oxide species was found to play an important role in the appearance of a highly efficient reactivity. The anatase-type TiO2 catalyst with large band gap and numerous surface OH groups showed high efficiency for the formation of CH4. Detection of Ti3+, H, C and CH3 radicals by electron spin resonance at 77 K suggests that the photoreaction of CO2 with H2O proceeds via the formation of CO and C radicals from CO2. The Cu-loading on the small powdered TiO2 catalyst brought about new formation of CH3OH, and the Cu+ species on TiO2 were found to play a significant role in this photocatalytic reaction. In the case of single crystals of rutile TiO2, the surface of TiO2(100) exhibited a higher efficiency for the formation of CH4 and CH3OH than TiO2(110). Measurements of the intermediate species formed on the TiO2(100) single crystal were carried out using high resolution electron energy loss spectroscopy.