Catalytic Intermediates of CO₂ Hydrogenation on Cu(111) Probed by In Operando Near-Ambient Pressure Technique

The in operando monitoring of catalytic intermediates is crucial for understanding the reaction mechanism and for optimizing the reaction conditions to improve the efficiency of the catalytic protocol; however, until now, this has remained a daunting challenge. Herein, we investigated the interaction of CO₂ and H₂ with the Cu(111) surface in a CO₂ hydrogenation model system by using the in operando technique of near-ambient pressure X-ray photoelectron spectroscopy, which is further assisted by ultraviolet photoemission spectroscopy and low-energy electron diffraction (LEED) measurements. These techniques allowed the direct observation of CO₂ dissociation into CO+O on the Cu(111) surface and the adsorption of O on the surface at room temperature. The intermediate HCOO^- was unambiguously detected in the CO₂ +H₂ environment, which corroborated the formate pathway for methanol formation on the Cu(111) surface. We further found that O coverage can prevent the build up of graphitic carbon on the Cu surface. By taking advantage of the competitive interplay between Cu-O and graphitic carbon, we have proposed a feasible strategy for inhibition of the formation of graphitic carbon by tuning the CO₂ and H₂ partial pressures, which may contribute to sustaining the active Cu catalyst under the reaction conditions.