Dry Reforming of Methane on NiCu and NiPd Model Systems: Optimization of Carbon Chemistry

A series of ultra-clean, unsupported Cu-doped and Pd-doped Ni model catalysts was investigated to develop the fundamental concept metal doping impact on carbon tolerance catalytic activity in dry reforming methane (DRM). Wet etching with concentrated HNO3 a subsequent single sputter–anneal cycle resulted full removal an already existing oxidic passivation layer segregated and/or ambient-deposited surface bulk impurities yield ultra-clean substrates. Carbon solubility, support effects, segregation processes, cyclic operation temperatures, electronic ensemble effects were all found play crucial role stability these systems, as verified by X-ray photoelectron spectroscopy (XPS) characterization. Minor Cu promotion showed almost complete suppression coking moderate reduction activity, while high loadings facilitated growth alongside severe deactivation. The improved resistance stems from increased CH4 dissociation barrier, decreased solubility bulk, good prevailing CO2 activation properties enhanced CO desorption. Cyclic DRM surfaces content that is too leads impaired oxidation kinetics causes irreversible deposition. Thus, optimal stable NiCu composition region 70–90 atomic % Ni, which allows appropriate syngas production rate be retained total during DRM. In contrast, more Cu-rich systems limited under reaction conditions, leading undesired processes Cu. much higher deposition NiPd Pd results To achieve conversion de-coking, active oxide boundary required, allowing for clean-off re-segregated via inverse Boudouard reaction. diffusion depends strongly decreases following order: >