Identification of Highly Selective Surface Pathways for Methane Dry Reforming Using Mechanochemical Synthesis of...

The methane dry reforming (DRM) reaction mechanism was explored via mechanochemically prepared Pd/CeO₂ catalysts (PdAcCeO₂M), which yield unique Pd-Ce interfaces, where PdAcCeO₂M has a distinct reaction mechanism and higher reactivity for DRM relative to traditionally synthesized impregnated Pd/CeO₂ (PdCeO₂IW). In situ characterization and density functional theory calculations revealed that the enhanced chemistry of PdAcCeO₂M can be attributed to the presence of a carbon-modified Pd⁰ and Ce^4+/3+ surface arrangement, where distinct Pd-CO intermediate species and strong Pd-CeO₂ interactions are activated and sustained exclusively under reaction conditions. This unique arrangement leads to highly selective and distinct surface reaction pathways that prefer the direct oxidation of CH to CO, identified on PdAcCeO₂M using isotope labeled diffuse reflectance infrared Fourier transform spectroscopy and highlighting linear Pd-CO species bound on metallic and C-modified Pd, leading to adsorbed HCOO [1595 cm^-1] species as key DRM intermediates, stemming from associative CO₂ reduction. The milled materials contrast strikingly with surface processes observed on IW samples (PdCeO₂IW) where the competing reverse water gas shift reaction predominates.