Tuning the hydrogenation of CO2 to CH4 over mechano-chemically prepared palladium supported on ceria

CO2 methanation reactivity, reaction mechanism, and surface structure were investigated on a mechanochemically prepared Pd/CeO2 catalyst (PdAcCeO2-M), where an oxidative pretreatment (-o) increased methane yield by a factor of two compared to a reductive pretreatment (-h). Methanation rates were maintained for over 48 h and further increased upon oxidative regeneration treatments. The surface species of both PdAcCeO2-M-o and PdAcCeO2-M-h were explored via in situ CO2 and CO hydrogenation DRIFTS, where CO hydrogenation effectively models the dissociative CO2 mechanism (CO2 → CO → CH4). PdAcCeO2-M-o yielded distinct Pd-CO adsorption and the absence of monodentate carbonate at ∼ 1400 cm−1, while AP-XPS showed that PdAcCeO2-M-o yielded a unique Pdδ+ contribution at 335.9 eV. By gaining insights from various in situ spectroscopic techniques, and by breaking the CO2 hydrogenation mechanism into piecewise steps, a deeper understanding of the direct CO2 reduction towards methane and CO over mechanochemically prepared Pd/CeO2 catalysts was obtained.