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 H2/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–O 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.