High-Pressure CO2 Photoreduction, Flame Spray Pyrolysis and Type-II Heterojunctions: A Promising Synergy

In this work, three catalysts, TiO2, WO3 and TiO2/WO3, have been synthesized through flame spray pyrolysis synthesis (FSP) and have been tested for CO2 photoreduction. The catalysts were fully characterized by XRD, DRS UV–Vis, N2 physisorption and SEM. Experimental tests were performed in a one-of-a-kind high-pressure reactor at 18 bar. TiO2 P25 was used as a benchmark to compare the productivities of the newly synthetized catalysts. The two single oxides showed comparable productivities, both slightly lower than the P25 reference value (ca. 17 mol/kgcat·h). The mixed oxide, TiO2/WO3, instead showed an impressive productivity of formic acid with 36 mol/kgcat·h, which is around 2.5 times higher than both of the single oxides alone. The formation of a type-II heterojunction has been confirmed through DRS analysis. The remarkable productivity demonstrates how FSP synthesis can be a crucial tool to obtain highly active and stable photocatalysts. This approach has already been successfully scaled up for the industrial production of various catalysts, showcasing its versatility and efficiency.