Regulating CHO* intermediate pathway towards the significant acceleration of photocatalytic CO2 reduction to CH4 through rGO-coated ultrafine Pd nanoparticles

Tailoring catalytic reaction pathways by using reduced graphene oxide (rGO) to tune the electron-hole separation channels in the active sites of noble metals for achieving ideal yield and selectivity in photocatalytic CO2 reduction of hydrocarbon fuels remains a challenge. Herein, ternary catalyst of rGO-coated SnO2-supported noble metal Pd nanoparticles (Pd4/SnO2@rGO) has been prepared by coassembly between negatively charged graphene oxide and positively charged Pd nanoparticles. By coating with ultrathin rGO, the selectivity can be shifted from CO (44.69 % for Pd4/SnO2) toward CH4 as the prevalent species, in which the Pd nanoparticles acted as catalytic sites and electron capture sites. The rGO coating reduced the recombination of the photogenerated carriers as well as optimized the band gap and reduction potential of the catalyst. The in situ spectroscopic tests and density functional theory calculations revealed that CO2 adsorbed on Pd nanoparticles selectively formed dominant low-energy CHO* intermediates because of the generation of HCOOH* intermediates, thus providing a unique reaction pathway for the reduction of CO2 to CH4. Therefore, under sunlight irradiation, the CH4 selectivity of the catalyst is enhanced to 94.1 % with a production rate of up to 77.8 μmol·g−1·h−1. This work demonstrated the prospect to tune the electronic structure of Pd using rGO, which provided a strategy for enhancing the carbon dioxide reduction reaction and selectively obtaining CH4 products in photocatalytic systems.