Photoreduction of carbon dioxide with H2 and H2O over TiO2 and ZrO2 in a circulated photocatalytic reactor

The photocatalytic reduction of carbon dioxide (CO2) was studied in a self-designed circulated photocatalytic reaction system under titanium dioxide (TiO2, Degussa P-25) and zirconium oxide (ZrO2) photocatalysts and reductants at room temperature and constant pressure. The wavelengths of incident ultraviolet (UV) light for the photocatalysis of TiO2 and ZrO2 were 365 and 254 nm, respectively. Experimental results indicated that the highest yield of the photoreduction of CO2 were obtained using TiO2 with H2+H2O and ZrO2 with H2. Photoreduction of CO2 over TiO2 with H2+H2O formed CH4, CO, and C2H6 with the yield of 8.21, 0.28, and 0.20 μmol/g, respectively, while the photoreduction of CO2 over ZrO2 with H2 formed CO at a yield of 1.24 μmol/g. The detected reaction products supported the proposition of two reaction pathways for the photoreduction of CO2 over TiO2 and ZrO2 with H2 and H2O, respectively. Additionally, a one-site Langmuir–Hinshewood (L–H) kinetic model was successfully applied to simulate the photoreduction rate of CO2.