Photocatalytic reduction of CO2 by Pt-loaded TiO2 in the mixture of sub- and supercritical water and CO2

Photocatalytic reduction of CO2 by Pt-loaded TiO2 in the mixture of CO2 and water has been examined as a function of temperature and pressure up to 400 degrees C and 30 MPa. The abrupt increase in the yields of CO, CH4, HCOOH and HCHO was observed as temperature was elevated from 300 to 400 degrees C at a constant pressure of 30 MPa. This is attributed to the formation of uniform single phase mixture of water and CO2 under supercritical condition, leading to the enhanced efficiency of CO2 reduction. In contrast, the yield of H-2 produced by water reduction showed a monotonous increase with temperature because of the thermal acceleration of photocatalytic reaction. It is suggested that the control of the phase state of reaction medium has a key role in the determination of conversion efficiency for the photocatalytic reduction of CO2 with water. (C) 2016 Elsevier B.V. All rights reserved.