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

Photo-catalytic reduction of CO2 to methane was studied in CO2-saturated aqueous solution in presence of TiO2 photo-catalyst (0.1%, w/v) as a suspension using 350 nm light. CO2 methanation rate was very much enhanced in the presence of 2-propanol as a hole scavenger. In addition to CO2 reduction, photo-catalytic reduction of methanol in N2-purged system was also tried but no methane was generated in presence of TiO2 without 2-propanol. The yield of methane was quite low even in presence of 2-propanol in this system. In the methanol photolysis CO2 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 CH4 from CO2 does not proceed via methanol as an intermediate under these conditions. In the aerated system also, methane was produced during photolysis of TiO2 suspension in presence of 2-propanol and its yield was comparable to that in CO2-saturated system. This suggests that surface-adsorbed as well as in situ generated CO2 are equally responsible for methane formation through photo-reduction in presence of TiO2. In the aerated system, 45 μmol CO2 was produced by photo-degradation of 2-propanol. In O2-saturated system, the methane yield was lower as compared to that in aerated system whereas CO2 yield was higher. Overall, the yield of methane was quite high if extrapolated to per gram of TiO2.