Photocatalytic CO2 Reduction by Cu loaded TiO2 in the Twin Photoreactor

Currently in the carbon dioxide photocatalytic reduction, the efficiency is not high and is not always reproducible. In this thesis, we got high amount of products and increased the stability by adding hydrogen into the photoreactor. We studied the effects of the weight loadings and the valance states of copper on the efficiency of carbon dioxide reduction. Sol-gel method was used to synthesize titanium dioxide. Copper was loaded on titanium dioxide by incipient-wetness impregnation method. The variations of copper valence state were obtained under different calcination atmospheres. CuO was formed under air calcination while Cu was formed under H2 reduction. Several instruments, UV-Vis, SEM, EDS, XRD and XPS were applied to measure the light absorption, surface morphology, crystalline phase and chemical status. The valence change of copper was found from the oxidation to reduction states before and after the reaction. In the vapor-phase photoreaction, an UVC lamp was used as the light source 254 nm and the light intensity 12 mW/cm2. The temperature was raised up to 90oC. The reaction were carried out by using TiO2, 1%CuO/TiO2, 2%CuO/TiO2, 1%Cu/TiO2 and 2%Cu/TiO2 under 0.01 atm hydrogen. The results revealed that the reduced copper had higher activity for the CO2 reduction under these conditions. There was not much difference in yields between 1%Cu/TiO2 and 2%Cu/TiO2. For these two catalysts, the highest yields were 28.72μmol/g methane, 5.74μmol/g CO and 26.13μmol/g methane, 7.23μmol/g CO, respectively, in 8 hours. Thus, the 1%Cu/TiO2 was used in the twin reactor with Fe2+/Fe3+ as electron mediator. We used artificial sunlight, AM1.5G Xenon lamp, to irradiate the catalysts. Pre-treated Nation cation-exchanged membrane was used for separating two different solutions that were called oxygen side and reduction side. Pt/WO3 was put into the oxygen side solution. In the reduction side, hydrogen catalyst Pt/SrTiO3:Rh, was put into the solution. The hydrogen generated by the catalyst can be used as the hydrogen source of carbon dioxide reduction. 1%Cu/TiO2 was put on the quartz plate in the reduction side to contact with the carbon dioxide in the gas phase. The highest yields in reduction side are 0.5863μmol/g hydrogen, 0.2005μmol/g methane and 1.3008μmol/g CO.