Pivotal Role of Ni/ZrO2 Phase Boundaries for Coke-Resistant Methane Dry Reforming Catalysts

To identify the synergistic action of differently prepared Ni-ZrO2 phase boundaries in methane dry reforming, we compared an "inverse" near-surface intermetallic NiZr catalyst precursor with the respective bulk-intermetallic NixZry material and a supported Ni-ZrO2 catalyst. In all three cases, stable and high methane dry reforming activity with enhanced anticoking properties can be assigned to the presence of extended Ni-ZrO2 phase boundaries, which result from in situ activation of the intermetallic Ni-Zr model catalyst systems under DRM conditions. All three catalysts operate bifunctionally; methane is essentially decomposed to carbon at the metallic Ni-0 surface sites, whereas CO2 reacts to CO at reduced Zr centers induced by a spillover of carbon to the phase boundaries. On pure bulk Ni-0, dissolved carbon accumulates in surface-near regions, leading to a sufficiently supersaturated state for completely surface-blocking graphitic carbon segregation. In strong contrast, surface-ZrO2 modified bulk Ni-0 exhibits virtually the best decoking and carbon conversion conditions due to the presence of highly dispersed ZrO2 islands with a particularly large contribution of interfacial Ni-0-ZrO2 sites and short C-diffusion pathways to the latter.