Photocatalytic reduction of CO2 on CuO-TiO2 composite catalysts in the presence of methanol to prepare methyl formate had been investigated. Methanol was used as sacrificial reagent to react with the photogenerated holes in the valence band, and CO2 was reduced by the electrons in the conduction band. CuO-TiO2 was optimized for CuO loading, preparation method and calcination temperature. The catalyst of 1.0CuO-TiO2, calcined at 450 degrees C and CTAB as a dispersant showed the highest overall activity. The heterojunction between CuO and TiO2 demonstrated with HRTEM played an important role in enhancing the photocatalytic activity. (C) 2010 Elsevier Inc. All rights reserved.