Mo2Ti2C3TX MXene performance in catalytic CO2 hydrogenation and its promotion with single Pt atoms

Mo₂Ti₂C₃T_x MXene materials, bare or loaded with strongly anchored single Pt atoms, were investigated using various methods, including STEM, XPS, XAS and DFT calculations. Upon Pt impregnation, the delaminated Mo-rich MXene surface undergoes partial oxidation, which is reversed by an H₂ thermal treatment at 400 °C. The optimized MXene shows high catalytic activity for CO₂ hydrogenation to CO and smaller amounts of methane and methanol. Around and above the pretreatment temperature of 400 °C, the MXene is gradually defunctionalized from O- and F-containing groups and depleted in carbidic carbon, leading to deactivation. Single Pt atoms are cationic after impregnation, and reduce upon H₂ treatment, filling surface Mo vacancies. Pt addition increases the MXene activity, in particular by facilitating H₂ dissociation, but has little effect on the single-atom catalyst selectivity and on the rate dependence upon reactant partial pressures. The lowest Pt loading leads to the highest turnover frequency, indicating that the MXene surface sites are key to CO₂ activation.