Photocatalytic Conversion of CO2 in H2o over Solid Based Materials

Abstract

Conversion of the greenhouse gas CO2 into carbon and useful carbon sources such as CO, HCOOH, HCHO, CH3OH, and CH4 is a potential method of solving energy and environmental problems. Photocatalytic conversion of manmade CO2 is attractive from the viewpoint of sustainable energy production and greenhouse gas reduction. Layered double hydroxides (LDH) are synthetic or natural crystalline clays that consist of brucite (Mg(OH)2)-like positively charged two-dimensional sheets in which some divalent cations such as Mg2+ are substituted by trivalent cations; further, water and exchangeable charge-compensating anions are present in the interlayer. In this study, we carried out the photocatalytic conversion of CO2 in H2O using various LDHs. Considerable amount of CO was obtained over various LDHs in the photocatalytic conversion of CO2 and photocatalytic H2 evolution from H2O competitively took place in all cases. Ni-Al LDH exhibited high selectivity to CO because the amount of H2 evolved was relatively low. Ni-Al LDH (Ni/Al = 4) which was aged for 20 h under hydrothermal condition at 383 K after coprecipitation showed the highest activity for the evolution of CO. GC/MS analysis for the photocatalytic conversion of 13C-labeled CO2 clarified that 13CO (m/z = 29) was evolved in priority to 12CO (m/z = 28). Accordingly, CO2 introduced in the gas phase was adsorbed on the surface of LDHs, and then reduced into CO in the photocatalytic conversion of CO2 in water.