Carbon Nitride-Based Catalysts for High Pressure CO2 Photoreduction

In the current research, the productivity of CO2 photoreduction has been boosted by performing the reaction in an innovative photocatalytic reactor, which allows for operation up to 20 bar. A set of photocatalysts were used, including three types of pristine TiO2, i.e., one commercially prepared (Evonik P25), one home-prepared by flame spray pyrolysis (FSP), and one obtained by the hydrolysis of TiCl4 (TiO2exCl), a bare thermo-exfoliated carbon nitride (C3N4-TE), and binary materials composed of TiO2 and C3N4-TE. The photoreduction was carried out in water at pH 14 and in the presence of Na2SO3 as a hole scavenger. Hydrogen and very small amounts of CO were detected in the head space of the photoreactor, while in the liquid phase, the main product was formic acid, along with traces of methanol and formaldehyde. The composites P25/TE and TiO2exCl/TE were found to have a higher productivity if compared to its single constituents used alone, probably due to the heterojunction formed by coupling the two materials. Moreover, the high pressure applied in the photoreactor proved to be very effective in boosting the yield of the organic products.