Mechanism of CH₄ Dry Reforming on Nanocrystalline Doped Ceria-Zirconia with Supported Pt, Ru, Ni, and Ni–Ru

Specificity of CH₄ dry reforming mechanism for Me-supported doped ceria-zirconia catalysts with high oxygen mobility was elucidated using a combination of transient kinetic methods (TAP, SSITKA) with pulse microcalorimetry and in situ FTIRS. Steady-state reaction of CH₄ dry reforming is described by a simple redox scheme with independent stages of CH₄ and CO₂ activation. This is provided by easy CO₂ dissociation on reduced sites of oxide supports followed by a fast oxygen transfer along the surface/domain boundaries to metal sites where CH₄ molecules are transformed to CO and H₂. The rate-limiting stage is irreversible transformation of CH₄ on metal sites, while CO₂ transformation proceeds much faster being reversible for steady-state surface. The oxygen forms responsible for CH₄ selective transformation into syngas correspond to strongly bound bridging oxygen species with heats of desorption ≈600–650 kJ/mol O₂, most probably bound with pairs of Pr and/or Ce cations able to change their oxidation state. Ni + Ru clusters could be involved in CO₂ activation via facilitating C–O bond breaking in the transition state, thus increasing the rate constant of the surface reoxidation by CO₂. Strongly bound carbonates are spectators.