Influence of oxygen mobility on catalytic activity of La–Sr–Mn–O composites in the reaction of high temperature N 2O decomposition

Abstract

Previous study suggested that either high oxygen mobility in layer-structured (La 1− y Sr y ) 2MnO 4 perovskite or high oxygen diffusion through intergrain boundaries is the reason why multiphase La 1− x Sr x MnO 3 samples exhibit a high catalytic activity in high temperature N 2O decomposition. The absence of inhibiting effect of oxygen on the reaction rate for these samples allows us to suppose that surface segregation of layered perovskite increases oxygen mobility and facilitates oxygen desorption from the surface. In this paper, we aimed at determining the influence of surface composition on oxygen mobility and catalytic activity in high temperature N 2O decomposition. By means of steady-state isotopic transient kinetic analysis (SSITKA) the mechanism and kinetics of oxygen exchange were elucidated for three La 1− x Sr x MnO 3 ( x = 0, 0.3, and 0.5) samples considerably differing in phase composition and catalytic activity. The results obtained indicate that inactive single-phase LaMnO 3 exhibits both the lowest rate of oxygen exchange on the surface and the lowest rate of oxygen diffusion in the bulk. For La 0.3Sr 0.7MnO 3, the increased values of both rates as compared with LaMnO 3 can be interpreted as the appearance of a fast pathway of oxygen transfer through vacancies formed in the perovskite lattice to compensate the reduced cation charge. The highest values of the content of fast-exchangeable oxygen and oxygen diffusion coefficient were found for a multiphase sample containing layered perovskite, thus providing a strong correlation between oxygen mobility and catalytic activity in the reaction of nitrous oxide decomposition.