Photocatalytic CO₂ Reduction under Continuous Flow High‐Purity Conditions: Influence of Light Intensity and H₂O Concentration

Abstract

Abstract The present study deals with fundamental investigations on the effect of light energy and intensity on the photocatalytic reduction of CO 2 on TiO 2 P25 under high purity continuous flow conditions. In accordance with previous works, gas chromatographic (GC) online detection identified CH 4 as the main product of photocatalytic CO 2 reduction. It was found that the product formation is dependent on the light intensity, which verifies that CH 4 is formed in a photon induced process on TiO 2 . A variation of the light intensity revealed that charge carrier recombination is more strongly enhanced compared to the charge transfer reaction to adsorbed species. On these grounds, the rate of CH 4 formation increases only by the square root of the light intensity. Furthermore, product formation is predominantly a UV photon driven process. A further part of this study investigated the effect of H 2 O on the CH 4 formation. The photocatalytic removal of carbon‐containing species and the CO 2 reduction can already proceed with traces of adsorbed H 2 O, whereas a continuous flow of gaseous H 2 O results in an inhibition of product formation. Based on our study, we can identify highly promising routes for photocatalyst improvement.