Rh/TiO2 samples, which have been found to be effective for photoenhanced reduction of CO2 by H-2 were characterized by means of infrared spectroscopy and X-ray absorption spectroscopy. Infrared study revealed that adsorbed CO arose even on a strongly reduced samples which showed low activity toward the reaction. Taking the results of X-ray absorption into consideration, it was proposed that the mixture of rhodium in metallic and oxidized states was effective for the release of the adsorbed CO to the gaseous phase. Infrared and X-ray absorption studies further showed that prolonged photoreaction caused the decrease in the particle size of rhodium, and consequently, the ability for the electron transfer from Rh/TiO2 to adsorbates. This is the reason for the deactivation observed during the photoreaction. (C) 2001 Elsevier Science BN. All rights reserved.