Photocatalytic reduction of carbon dioxide in the presence of nitrate using TiO2 nanocrystal photocatalyst embedded in SiO2 matrices

Photocatalytic reduction of CO2 in the presence of nitrate ions in various solvents was studied using TiO2 nanocrystals embedded in SiO2 matrices as photocatalysts. Both formate and carbon monoxide were produced as the reduction products of CO2, ammonia as the reduction product of nitrate, and in addition to these products, urea was formed as a major reduction product of both CO2 and NO3-. The selectivity of these reactions was greatly influenced by the kind of solvents used, and with increasing the dielectric constant of solvents, the amount of formate and carbon monoxide produced decreased, while those of urea and ammonia increased. These results suggest that the reduction reaction of nitrate ions was the rate-determining step of the formation of urea. (C) 1998 Elsevier Science S.A. All rights reserved.