Shashkova T. Catalytic properties of composites based on zirconia and transition metal oxides (Cu, Co, Ni) in the oxidation of methane

The thesis is devoted to studying the influence of transition metal oxides (CuO, CoO, NiO) and platinum group metals (PGM: Pd, Pt, Rh) in composites based on yttrium- (scandium-) stabilized zirconia, as prototypes of anode materials of solid oxide fuel cells (SOFC), on their catalytic activities in oxidative conversion of methane. It is shown that composites based on Y-stabilized zirconia and transition metal oxides (CuO, CoO, NiO) show high activity in the heterogeneous catalytic oxidation (deep and partial) of methane: 75-99 % conversion of CH4 is achieved in the temperature range of 600-800 °C - typical for SOFC. Regulation of quantity and mobility of surface oxygen in such systems by optimizing the composition allows to increase their activity. The most active composite (10 %Со,10 %Ni/[YSZ+CeO2]) towards deep oxidation of methane possesses a spinel structure (Сu1-ХCo2+ХO4) which is more active and stable under oxidative process conditions. Increase in activity of composite catalysts, doped by PGM, which is shown for Pd-containing sample, is connected to their influence on redox properties of oxide composites. It is shown that promoting effect of platinum group metals (Pd, Pt, Rh) depends on the composition of the reaction mixture (stoichiometry of partial or deep oxidation, presence of sulfur dioxide). Higher activity of Pt-containing catalyst in partial and deep oxidation of methane in the presence of SO2 is caused by much greater activity of platinum in oxidation of sulfur dioxide and corresponding reduction of active surface blocking by SO2. Binary Сo-Cu and Ni-Cu сomposites based on YSZ displayed high enough thermal stability (up to 1000 С) in the process of methane deep oxidation.