Conversion of the greenhouse gas CO2into carbon and useful carbon sources such as CO, HCOOH, HCHO, CH3OH,and CH4 is a potential method of solving energy and environmentalproblems. Photocatalytic conversion of manmade CO2 is attractivefrom the viewpoint of sustainable energy production and greenhouse gasreduction. Our group found that CO is generated in the photocatalyticconversion of CO2 over ZrO2, MgO, ATaO3 (A =Li, Na, and K), and Ga2O3, which have the properties ofsolid base catalysts, in the presence of H2 or CH4(reductant). However, these oxides did not function as a photocatalyst inwater. Layered double hydroxides (LDH) are synthetic or natural crystallineclays that consist of brucite (Mg(OH)2)-like positively charged two-dimensionalsheets in which some divalent cations such as Mg2+ are substituted bytrivalent cations; further, water and exchangeable charge-compensating anions arepresent in the interlayer. Mg-Al LDH catalyzes the aldol condensation ofcarbonyl compounds in aqueous solution because of the high water tolerance of thesurface base sites. In this study, we carried out the photocatalytic conversionof CO2 in H2O using various LDHs. Considerable amount of CO andtiny amount of CH4 were obtained over Mg-Al, Ni-Al, Mg-In, Ni-In,Zn-Al LDHs. Photocatalytic H2 evolution from H2O competitively tookplace in all cases. In the case of Ni-Al LDH, CO was obtained with highselectivity. GC/MS analysis for the photocatalytic conversion of 13CO2clarified that CO2 introduced in the gas phase is reduced into CO inH2O under photoirradiation.

Photocatalytic conversion of CO2 in H2O using layered double hydroxides (LDHs)

247th National Meeting (2014)

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