Magnesium modified TiO2 photocatalyst has been found to improve the CO2 photoreduction reaction, with a high selectivity towards CH4. Thus, Mg-TiO2 has been synthesized with different compositions up to 2.0 wt%. Unlike the bare TiO2, the surface reorganization originated by the presence of Mg enhances the formation of methane by a factor of 4.5, corroborating that complete reduction of CO2 is achieved. It was found that the enhancement of the overall photocatalytic activity towards carbon dioxide reduction can be increased by a factor of 3, revealing a straightforward correlation with the surface states induced by the presence of the doping element. Finally, the evolution of the selectivity versus methane formation against hydrogen is discussed for the different magnesium loadings. (C) 2013 Elsevier B.V. All rights reserved.