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

Abstract

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.