Photocatalytic reduction of CO2 using H2 as reductant over ATaO3 photocatalysts (A = Li, Na, K)

ATaO3 (A = Li, Na, K) compound oxides exhibit photocatalytic activity for the reduction of CO2 in the presence of H2. Only CO gas was generated over all samples under photoirradiation. The photocatalytic activity was higher in the order corresponding to KTaO3, NaTaO3 and LiTaO3 (LiTaO3 > NaTaO3 > KTaO3). The order of the photocatalytic activities was consistent with that of the Eg (optical gap) values. After 24 h of photoirradiation, the amount of evolved CO reached 0.42 μmol g−1 over LiTaO3. TPD experiments indicated that the broad peak which is assigned to chemisorbed CO2 gas was observed at 573 K in the case of LiTaO3. On the contrary, there was no peak in the spectra of NaTaO3 and KTaO3. The amount of evolved CO gas almost strongly depends on the amount of chemisorbed CO2 in the case of ATaO3 (A = Li, Na, K). In addition, the photocatalytic activity increased with increasing the calcination temperature of LiTaO3. This means that a smooth charge separation in a LiTaO3 photocatalyst and chemisorption of CO2 on the surface contribute to effective reduction of CO2 in the presence of H2.