Ceria-Based Fluorite-Like Oxide Solid Solutions as Catalysts of Methane Selective Oxidation into Syngas by the Lattice Oxygen: Synthesis, Characterization and Performance

摘要

Catalytic oxidation of methane (natural gas) into syngas by oxygen transferred through the membranes comprised of complex oxides with mixed ionic-electronic conductivity is now considered as a vial option in the natural gas conversion technologies including such application as hydrogen generation for fuel cells. Ceria modified by low-valence cations (Sm, Bi etc) possess a good ionic conductivity, while electronic conductivity can be generated either by forming nanocomposites with precious metals (Pt, Ag etc) or through a partial reduction of those mixed oxides. For a side of membrane contacting with methane, the rate and selectivity of methane transformation into syngas and/or combustion products is expected to depend upon the surface oxygen bonding strength and mobility determined in turn by the mixed oxide chemical composition and real structure. Moreover, specific activation of methane on the metallic components (Pt etc) could be important as well. However, this aspect of the catalytic oxygen conducting membranes design has not yet been properly addressed. It is also of primary importance for design of mixed oxide catalysts able to convert methane into syngas by the lattice oxygen in red-ox cycles (with reoxidation of reduced systems by air or even by water or carbon dioxide) or by the gas -phase oxygen at short contact times on monoliths.