Photocatalytic conversion of CO2 into fuels could mitigate global warming and energy shortage simultaneously. In this study, the reaction pressure was optimized for CO2 reduction by H-2. The major products were methane, CO, and methanol, and the observed catalytic activity order was Cu or Pd on TiO2 >> Ag/ZrO2 similar to g-C3N4 > Ag/Zn3Ga-layered double hydroxide similar to BiOCl. Hot/excited electrons due to surface plasmon resonance could be transferred to CO2-derived species and the remaining positive charge could combine with excited electrons in the semiconductor. As the levels of hot/excited electrons became more negative, the catalysts became more active, except for Ag/ZrO2 and Ag/Zn3Ga-LDH, probably due to lower charge separation efficiency for intrinsic semiconductors or hydroxides. The reaction order was controlled by the partial pressure of H-2, demonstrating preferable adsorption of H on Pd. The photoconversion of CO2 into methane was optimum at P-H2 = 0.28 MPa and P-CO2 = 0.12 MPa, but the rates gradually dropped at higher partial pressures due to adsorption of CO2 being hindered by H. (C) 2016 Elsevier Inc. All rights reserved.