Regulation of Electron Transfer and Microstructure in RuN Single-Atom Catalysts and Their Catalytic Performance for CO/CO₂ Hydrogenation

In this study, we developed a new type of Ru–N–C single-atom catalyst (SAC) with an excellent catalytic performance for CO/CO2 selective hydrogenation. RuN SACs were synthesized by constructing defects in the support with different coordination numbers and anchoring Ru species onto these vacancies. Three RuNx SACs (x = 2, 3, and 4) were synthesized: RuN2 and RuN4 SACs, which were obtained by direct calcination, and RuN3, which was obtained by high-temperature shock (HTS). HTS combined electrostatic adsorption and strong thermal coupling to anchor Ru atoms to N vacancies with a novel three-dimensional structure. The resulting RuN SACs exhibited excellent catalytic performance for the selective methanation of CO/CO2; in particular, RuN3 achieved a CO conversion of 99% and a CH4 selectivity of 95% under a gas hourly space velocity (GHSV)of 4255 h–1 at 150 °C. Electron transfer was observed between the Ru and N species, facilitating the formation of electron-deficient centers over the catalyst surface, which actively captured CO molecules, even at low CO pressures. Moreover, RuN SACs facilitated the breakage of the C–O chemical bond during the CO hydrogenation reaction and formation of a highly selective alkane product (CH4). Although the hydrogenation of CO2 was performed simultaneously, its reactivity was lower, and only a small amount of CO gas was released to the atmosphere. Additionally, Ru atoms in RuN3 possessed a unique protruding structure supported by the N species, which interacted with the reaction species at a high flux. Therefore, our novel RuN SACs can completely remove the CO species from H2-rich gas, which is beneficial for the stable operation of proton-exchange membrane fuel cells (PEMFCs).