Effect of La as Promoter in the Photoreduction of CO2 Over TiO2 Catalysts

In this work, TiO2 has been modified by treating it thermally together with different proportions (0.5–15 wt%) of La2O3. The resulting materials have been extensively characterized by XRD, TEM, N2 adsorption isotherms, temperature-programmed CO2 desorption, Raman, UV–Vis photoluminescence and X-ray photoelectron spectroscopies. The activity tests of these materials for the gas-phase photocatalytic reduction of carbon dioxide show that the main products of the reaction are in all cases CO and CH4, together with H2 from the parallel reduction of water. After the preparation procedure, La phases are best described as oxycarbonates, and lead to improved activity with respect to TiO2 with La contents up to 5 wt%. Higher loadings do not, however, lead to further enhanced activity. Retarded electron–hole recombination and enhanced CO2 adsorption are invoked as the key factors contributing to this activity improvement, which is optimized in the case of 0.5 wt% La leading to higher productions of CO and CH4 and increased quantum efficiency with respect to titania.