Title : Nanocomposite materials for structured catalysts of fuels reforming, catalytic layers in membrane reactors for oxygen and hydrogen separation and fuel cell anodes operating in the internal reforming mode
Abstract:
Approaches to design of nanocomposite materials for advanced energy field including structured catalysts for fuels transformation into syngas, reactors with oxygen and hydrogen separation membranes for fuels conversion into syngas and hydrogen, solid oxide fuel cells operating in the internal reforming mode are developed. These materials are comprised of mixed ionic-electronic conducting oxides (including high entropy samples) with perovskite, spinel, fluorite and Ruddlesden-Popper (RP) structures, ionic conductors (doped ceria, tungstates, molybdates and scandates of lanthanoids, etc.), prepared via Pechini route, in supercritical fluids, one-pot evaporation induced self-assembly method, etc.), electronic conductors (nanoparticles of Ni-based alloys, etc.) and their nanocomposites sintered by advanced methods (microwave sintering and e-beam sintering). Their real structure was characterized by modern structural (TEM with EDX, XRD) and spectral methods (EXAFS, XPS, UV-Vis, FTIRS of adsorbed CO, etc.), and their transport features were studied by impedance spectroscopy and oxygen isotope heteroexchange with C18O2 in the temperature- programmed mode. Several channels of oxygen migration exist in these systems with diffusion coefficients differing by several orders of magnitude, with fast channels corresponding to interfaces in nanocomposites, grain boundaries in complex oxides and to cooperative mechanism of migration in oxides with RP structure. Metal substrates for structured catalysts (microchannel plates, foils and foams) were covered by La2Zr2O7 - LaAlO3 layers and then by porous catalytic nanocomposite layers sintered by e-beam. Ni-Al foam substrates were used as carriers for design of multilayer oxygen and hydrogen separation membranes with catalytic layers supported on their fuel side, as well as anode substrates with Ni/electrolyte nanocomposites covered by dense layers of electrolytes along with perovskite+ fluorite cathode nanocomposites and catalytic nanocomposite layers on the anode side. Structured catalysts were tested in pilot reactors (including equipped with internal heat exchangers) in steam, dry, partial oxidation and autothermal reforming of biofuels at short contact times using concentrated feeds. A high yield of syngas approaching equilibrium and stable performance without coking were demonstrated even for glycerol, acetic acid, acetone, sunflower and turpentine oils. A high catalytic activity and coking stability in biofuels reforming were provided by high oxygen mobility in active components via bifunctional mechanism of reactions including oxygen species generation by support surface sites reoxidation by oxidants, their fast migration to metal alloy nanoparticles and reaction with activated fuel fragments producing syngas, along with absence of heat and mass transfer limitations ensured by structured substrates.
Optimized nanocomposite materials demonstrated a high power density and stable performance as SOFC cathodes and anodes operating in the internal mode of methane reforming (with power density exceeding that of cells with traditional cathodes and anodes). Asymmetric oxygen and hydrogen separation membranes with supported catalytic layers on the fuel side fed by fuels or their mixture with steam or carbon dioxide provided high oxygen/hydrogen fluxes in the intermediate temperature range promising for practice along with a high fuels conversion and hydrogen/syngas yield.
Support by the Russian Science Foundation grant 23-73-00045 is gratefully acknowledged
