PHOTOCATALYTIC CONVERSION OF CO2 IN H2O USING LAYERED DOUBLE HYDROXIDES (LDHS)

摘要

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. Our group found that CO is generated in the photocatalytic conversion of CO2 over ZrO2~1 MgO~2, ATaO3 (A = Li, Na, and K)~3, and Ga2O3~4, which have the properties of solid base catalysts, in the presence of H2 or CH4 (reductant). However, these oxides did not function as photocatalysts in water. Layered double hydroxides (LDHs) are synthetic or natural crystalline clays that consist of brucite (Mg(0H)2)-like positively charged two-dimensional sheets in which some divalent cations such as Mg~(2+) are substituted by trivalent cations; further, water and exchangeable charge-compensating anions are present in the interlayer. Mg-Al LDH catalyzes the aldol condensation of carbonyl compounds in aqueous solution because of the high water tolerance of the surface base sites.5 In this study, we carried out the photocatalytic conversion of CO2 in H2O using various LDHs.