Photo-catalytic reduction of carbon dioxide to methane using TiO 2 as suspension in water

Abstract

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 60×10 −8 mol to 200×10 −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 μmol 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.