DARK CATALYTIC REDUCTION OF CO2 OVER PHOTO-PRETREATED NIO/KSGR CATALYST

A NiO/ksgr (kieselguhr) catalyst was pre-irradiated in hydrogen atmosphere and subjected to flowing CO2 in the dark. CH4 Was preferentially formed, with small amounts of C2H6 and C3H8 also detected. The reduction of CO2 Was performed by chemisorbed hydrogen atoms which were produced during the pre-irradiation of the catalyst in H-2. By the bandgap excitation of NiO, electron-hole pairs are generated, H-2 is oxidized by h+ (conduction), and H+ is reduced by e- (valence) to form adsorbed H atoms. Further reduction of CO2 by the chemisorbed hydrogen was discussed based on a reaction scheme involving an enol form of formaldehyde as the intermediate.