Ceria-based fluorite-like oxide solid solutions as catalysts of methane selective oxidation into syngas by the lattice oxygen: synthesis, characterization and performance

Polymerized precursor route [M.P. Pechini, US Patent 3, 330 (1967) 697] was applied for synthesis of dispersed ceria-based solid solutions Ce1-xMex3+O3-y (Me3+ = Sm3+ or Bi3+, x up to 0.5). The surface properties of those samples were modified by supporting Pt. Their bulk and surface structural features were characterized by using XRD, TEM, EXAFS, X-ray wide angle scattering (RED), UV-vis, Raman, FTIRS of lattice modes and adsorbed CO. To elucidate factors controlling the surface/bulk oxygen mobility and reactivity, these results were compared with the data of the oxygen isotope exchange and/or H-2/CH4 temperature-programmed reduction (TPR). Single-phase fluorite-like solid solutions with a nanodomain microstructure are characterized by distortion of the coordination polyhedra caused by dopants followed by the lattice local rearrangement into that of a lower symmetry at a high dopant content. The highest performance in methane selective oxidation into syngas by the lattice oxygen is found for samples where isolated oxygen vacancies dominate. Earlier studied Pt/Ce-Zr-La-0 system [Stud. Surf. Sci. Catal. 143 (2002) 659; T.G. Kuznetsova, V.A. Sadykov, S.A. Veniaminov, G.M. Alikina, E.A. Paukshtis, Ya.N, Kulikova, E.M. Moroz, E.B. Burgina, V.A. Rogov, V.N. Kolomiichuk, V.V. Kriventsov, D.I. Kochubei, O.N. Martyanov, V.F. Yudanov, I.S. Abornev, S. Neophytides, ISO22, Europacat VI, September 2003, Innsbruck, Austria] has a lower oxygen mobility, is less stable in redox cycles and less selective for syngas. Bi-Ce-O system mainly combusts methane and is irreversibly decomposed by deep reduction due to metallic Bi evaporation. (C) 2004 Elsevier B.V. All rights reserved.