Abstract:  Photocatalytic reduction of CO₂ by water was performed in the presence of a Ag/TiO₂ catalyst under illumination by lamps with different wavelengths (254, 365, and 400 nm). The yields of the main products (methane and methanol) were higher with the 254 nm lamp than with the 365 lamp while no products were observed with the 400 nm lamp. This was because the electron-hole generation rate increased with increasing energy of irradiation (decreasing wavelength) and there were higher densities of electron states at higher energies in TiO₂. The increased efficiency of electron-hole generation with a shorter wavelength irradiation increased the efficiency of the catalyst. The energy of the electrons excited by visible light (400 nm) was too low for CO₂ photocatalytic reduction.

Key words: silver doping, titania, carbon dioxide reduction, photocatalysis, wavelength