Tuning the hydrogenation of CO2 to CH4 over mechano-chemically prepared palladium supported on ceria
Maila Danielis, Juan D. Jiménez, Ning Rui, Jorge Moncada, Luis E. Betancourt, Alessandro Trovarelli, José A. Rodríguez, Sanjaya D. Senanayake, Sara Colussi
Abstract
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.