Efficient Photo-Assisted Thermal Catalytic CO2 Methanation by Synergy of Ru Single Atoms and Ni Nanoparticles

Abstract Photoassisted thermal (PAT) catalytic CO2 methanation represents one of the most pivotal chemical conversion routes for the resource utilization of CO2. However, current PAT catalysts still suffer from inadequate low-temperature catalytic activity and high recombination rates of photogenerated carriers. Herein, efficient low-temperature PAT CO2 methanation was achieved by constructing a synergistic catalytic system between Ru single-atom-doped CeO2 and Ni metal nanoparticles (Ni/CeRux, x = 0.01, 0.025, 0.05, and 0.10). Synchrotron radiation characterization results confirmed that Ru was doped into the lattice of CeO2 in the form of single atoms, which induced the formation of abundant surface oxygen vacancies (Ov) and enhanced the adsorption and activation of CO2 molecules. In situ X-ray photoelectron spectroscopy analysis revealed that Ru doping and light irradiation facilitated electron enrichment on the Ni surface, thereby promoting H2 dissociation and CO adsorption. Additionally, Ru doping narrowed the bandgap of CeO2, expanded its light absorption range, suppressed the recombination of photogenerated carriers, and strengthened the photothermal effect. Compared with the Ni/CeO2 catalyst, the Ni/CeRux catalysts exhibited improved low-temperature methanation performance, with an optimal Ru doping amount identified. Specifically, the Ni/CeRu0.025 catalyst achieved a maximum CH4 production rate of 223 mmol gcat−1 h−1 at 225 °C under a light intensity of 1.2 W cm−2. Moreover, the catalyst demonstrated sustained stability; after 100 h of continuous reaction, the conversion of CO2 remained at approximately 76%, and the CH4 selectivity remained above 99.6%. In situ diffuse reflectance infrared Fourier transform spectroscopy results indicated that formate (HCOO*) served as the dominant reaction intermediate. Density functional theory calculations further demonstrated that Ru single-atom doping regulated the stabilization and transformation of intermediates involved in the formate pathway, altered the rate-determining step (RDS) of the reaction, and reduced its energy barrier, thereby accelerating the overall reaction process. This work developed a synergistic catalytic system based on Ru single atoms and Ni nanoparticles for low-temperature CO2 methanation, providing a promising strategy for the efficient resource utilization of CO2.