Photo-enhanced reduction of carbon dioxide with hydrogen over Rh/TiO2

Photoreduction of gaseous carbon dioxide to carbon monoxide with hydrogen over Rh-loading TiO2 was investigated. As the reaction proceeded even in the dark but was enhanced under irradiation, the reaction should be considered as "photo-enhanced reaction". When Rh in Rh/TiO2 was strongly reduced to be in a fully metallic state, the activity was lowered and the main product changed from CO to CH4. A similar effect was obtained by changing the loading amount of Rh: when the loading amount of Rh was raised, the activity was lowered and the main product shifted from CO to CH4. The results of an X-ray absorption spectroscopic analysis showed that the ratio of Rh in a metallic state to that in an oxidized stale increased along with the increase of the amount of Rh loading on Rh/TiO2. The photocatalytic activity was higher as Rh was richer in the component of metallic and oxidized state. (C) 1999 Elsevier Science S.A. All rights reserved.