(530c) Photocatalytic Conversion of CO2 and H2O to CO and CH4 by Cu/TiO2-SiO2 Nanocomposites
The rapid increase in atmospheric CO2 levels has been recognized as the principal cause of current trends in global warming. Besides sequestering CO2 in geological formations, it is more preferable to recycle CO2 as a fuel feedstock. The recent innovations and advances in the photocatalysis technology have introduced CO2 conversion as a potentially promising application. This process utilizes ultraviolet (UV) and/or visible light as excitation source and converts CO2 and H2O into other valuable compounds such as syngas (CO and H2) and hydrocarbons (e.g. CH4 and CH3OH, etc). A variety of photocatalysts have been studied in literature and TiO2 based catalysts are the most convenient candidates in terms of cost and stability. Doping of transition metals such as copper on TiO2 was reported to enhance the photoreduction efficiency in that the metal particles serve as charge carrier receptors and reduce the rate of electron-hole pair recombination. In addition, batch reactors were used for most of the studies in literature for CO2 photoreduction, whereas, proper design of continuous flow reactors is desirable for potential scale-up of the technology. In this work, nanostructured Cu/TiO2-SiO2 composites were synthesized through a sol-gel method and by impregnation using CuCl2 as the Cu source. The highly porous structure of the Cu/TiO2-SiO2 composites gives a specific surface area over 300 m2/g, much larger than that of TiO2 nanoparticles (50 m2/g). The catalysts were applied in a continuous- flow reactor for photocatalytic conversion of CO2 and H2O under UV/visible light irradiation using a 400 W Xe lamp. The inlet CO2 flow rate was controlled at 3 ml/min and the reactor temperature was approximately 42 C. CO and CH4 were found to be the major reaction products in the gaseous phase. The production yield per unit mass of TiO2 was dramatically enhanced both due to the high surface area SiO2 substrate and due to the Cu doping. In addition, the production of CH4 was not observed without Cu doping, indicating possible involvement of Cu species in the chemical reactions. An optimal concentration of Cu loading on the catalyst is also being investigated in this study.