Enhanced catalytic performance of single-atom Cu on Mo₂C toward CO₂/CO hydrogenation to methanol: a first-principles study

Abstract

CO₂ emissions harm the environment due to their pivotal role in fostering climate change and ocean acidification. One way to take advantage of CO2 is to use it as a precursor to chemical materials to enable energy transition. The CO₂ to methanol conversion from green H₂ is a promising option. The silica-supported Cu/Mo₂CTₓ (MXene) catalyst displayed higher activity than the industrial reference system Cu/ZnO/Al₂O₃. To better understand CO₂ hydrogenation in Cu/Mo₂CTₓ and related processes under reaction conditions (CO hydrogenation and reverse water gas shift reaction), we performed periodic DFT calculations to evaluate the methanol synthesis reaction mechanism using our previously calibrated theoretical model against experiment characterization. Our results show the crucial role played by the Cu/Mo₂CTₓ interface in providing low-energy pathways to facilitate the hydrogenation of CO₂ to methanol, where both the Cu atom and the Mo₂CTₓ support participate in the reaction mechanism. The findings showcase the unique pathways provided by this supported single-atom catalyst, allowing the successive heterolytic cleavages of molecular hydrogen (H₂) to form HCOO*, HCOOH*, and H₂COOH* species with co-adsorbed hydrogen in contrast with classical heterogeneous catalysts based on Cu NPs supported on oxides. Thus, CH₃OH is readily formed under reaction conditions. CO also forms via the reverse water-gas shift (RWGS) reaction, which can be hydrogenated to methanol. These findings open new avenues to understanding CO₂ and CO hydrogenation by exploiting single-atom catalysts and metal-support interfaces.