Photo-catalytic reduction of carbon dioxide to methane using TiO2 as suspension in water

Photo-catalytic reduction of CO(2) to methane was studied in CO(2)-saturated aqueous solution in presence of TiO(2) photo-catalyst (0.1%, w/v) as a suspension using 350 nm light. CO(2) methanation rate was very much enhanced in the presence of 2-propanol as a hole scavenger. In addition to CO(2) reduction, photo-catalytic reduction of methanol in N(2)-purged system was also tried but no methane was generated in presence of TiO(2) without 2-propanol. The yield of methane was quite low even in presence of 2-propanol in this system. In the methanol photolysis CO(2) was found to be the main product with a yield of 60 x 10(-8) mol to 200 x 10(-8) mol. This shows that the generation of CH(4) from CO(2) does not proceed via methanol as an intermediate under these conditions. In the aerated system also, methane was produced during photolysis of TiO(2) suspension in presence of 2-propanol and its yield was comparable to that in CO(2)-saturated system. This suggests that surface-adsorbed as well as in situ generated CO(2) are equally responsible for methane formation through photo-reduction in presence of TiO(2). In the aerated system, 45 mumol CO(2) was produced by photo-degradation of 2-propanol. In O(2)-saturated system, the methane yield was lower as compared to that in aerated system whereas CO(2) yield was higher. Overall, the yield of methane was quite high if extrapolated to per gram of TiO(2). (C) 2004 Elsevier B.V. All rights reserved.