Photoreduction Of Co₂ In Methanol To Prepare Methyl Formate Using Cuo-tio₂

The rapid increase in the level of carbon dioxide is a matter of great concern. While discussions have begun on means to reduce carbon dioxide emissions, it is apparent that atmospheric carbon dioxide concentration will increase continuously and monotonically in the near future due to fossil fuel consumption. Suggestions have been made to capture and sequester carbon dioxide, although the ability to store several billion tons of carbon emitted in the form of carbon dioxide every year, the environmental consequences are questionable. Recycling of carbon dioxide via conversed into fine chemicals or high-energy content fuel which is suitable for use in the existed hydrocarbon based energy infrastructure, is an attractive option; however, the process is energy intensive and useful only if a renewable energy source can be used for the purpose. A possible pathway for the sustainable development is to use photocatalysts for the conversion of CO₂ into hydrocarbons with the help of solar energy. In this paper, the following were systematically investigated.Firstly, CuO-TiO₂ photocatalysts were prepared through a sol-gel method using CTAB as a dispersion agent . The prepared catalysts had small particle size and were well dispersed. The effects of CuO loading, preparation method and calcination temperature were studied. The optimum CuO loading was 1%. The catalysts prepared with CTAB had a small particle size so the surface area was large; the small particles were dispersed well so the agglomeration was avoided. The optimum calcination temperature was 450℃because at low calcination temperature the crystallization degree was low and at high calcination temperature the catalysts were sintered.Secondly, the catalysts were characterized by UV-Vis DRS,XRD and TEM to obtain the structure, crystal phase. The results of UV-Vis DRS indicated that the light absorption field had shifted to the visible light distinctly by CuO loading. XRD showed that the crystalline size was 13.8nm calculated from Scherrer formula and CuO was well-dispersed on the surface of TiO₂. From HRTEM the surface-phase junction between CuO and TiO₂ was visible. The formation of the junction could promote the spatial charge separation and enhance the photocatalytic activity.Thirdly, in the deaerated anhydrous system photocatalytic oxidation of methanol could produce methyl formate. The photocatalytic oxidation of methanol to methyl formate mainly proceeded through an intermediate of formaldehyde and followed by its dimerization.Finally, we used CuO-TiO₂ catalysts in the photoreduction of CO₂ with methanol as sacrifice reagent. Methanol reacted irreversibly with the photogenerated VB holes and could enhance the photocatalytic electron/hole separation resulting in higher quantum efficiency. CO₂ was reduced to formic acid and formaldehyde and then followed by esterification of formic acid with methanol and dimerization of formaldehyde via Tishchenko reaction. It was found that the presence of CO₂ could enhanced the methyl formate(MF) formation rate. The highest MF formation rate was 11420μmol/g/h, and the corresponding photoreduction rate of CO₂ was 6632μmol/g/h。...