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

Effect of complex oxide promoters and Pd on activity and stability of Ni/YSZ (ScSZ) cermets as anode materials for IT SOFC

Effect of fluorite-like or perovskite-like complex oxide promoters, Pd and Cu on the performance of Ni/8YSZ and Ni/ScCeSZ anode materials in CH4 steam reforming (SR) or selective oxidation (SO) by O-2 into syngas was studied. The spatial distribution of dopants in composites before and after contact with the reaction feed, features of components mutual interaction and forms of deposited coke were controlled by TEM combined with EDX analysis. The lattice oxygen mobility and reactivity were estimated by CH4 and H-2 temperature-programmed reduction (TPR), and the amount of deposited carbon after operation in the feed with stoichiometric H2O/CH4 ratio was estimated by the temperature-programmed oxidation. Promoters decrease the amount of deposited coke, while doping by Pd or Cu ensures also a good and stable performance at moderate (similar to 550 degrees C) temperatures required for the intermediate-temperature solid oxide fuel cells (IT SOFC) operation. (c) 2007 Elsevier B.V. All rights reserved.</p