Understanding the effect of co-doped N,Pd/TiO2 dopants on the efficiency and product selectivity of the photocatalytic CO2 reduction

Carbon dioxide photoreduction using solar energy has emerged as a promising strategy to address challenges related to climate change. TiO2 is the most used catalyst, due to its excellent properties regarding reagents adsorption, light absorption, and electron-hole pair recombination rate. Supercritical synthesis allows fine-tuning of its physicochemical and photocatalytic properties by simple changes in the synthesis conditions. In this work, this technique has been used to increase the TiO2 photocatalytic activity and selectivity to methane by doping it with metal (Pd) and non-metal elements (N). Regarding the mono-doped catalysts, it has been observed that nitrogen-doped TiO2 (0.1 wt%) exhibits an improved visible light sensitization, while the palladium-doped material (1-3 wt%) leads the selectivity towards low chain fuel hydrocarbons and provides active sites for CO2 reduction. These characteristics are further improved in the TiO2-based photocatalysts co-doped with N and Pd. Specifically, band gaps of N,Pd co-doped TiO2 are 0.4-0.6 eV lower, and photogenerated charges in the co- doped catalysts are separated more efficiently due to their lower resistance to charge transfer. In the case of the co-doped photocatalysts the CO2 conversion rates are 40 % larger than mono-doped TiO2, this increase being mainly due to CH4 production, which reaches a selectivity of 60 %.