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 H-2. 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 approximate to 600-650 kJ/mol O-2, 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.