Identification of Highly Selective Surface Pathways for Methane Dry Reforming Using Mechanochemical Synthesis of Pd-CeO 2 .

The methane dry reforming (DRM) reaction mechanism was explored via mechanochemically prepared Pd/CeO 2 catalysts (PdAcCeO 2 M), which yield unique Pd-Ce interfaces, where PdAcCeO 2 M has a distinct reaction mechanism and higher reactivity for DRM relative to traditionally synthesized impregnated Pd/CeO 2 (PdCeO 2 IW). In situ characterization and density functional theory calculations revealed that the enhanced chemistry of PdAcCeO 2 M can be attributed to the presence of a carbon-modified Pd 0 and Ce 4+/3+ surface arrangement, where distinct Pd-CO intermediate species and strong Pd-CeO 2 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 x to CO, identified on PdAcCeO 2 M 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 CO 2 reduction. The milled materials contrast strikingly with surface processes observed on IW samples (PdCeO 2 IW) where the competing reverse water gas shift reaction predominates.