Effect of surface decoration with LaSrFeO4 on oxygen mobility and catalytic activity of La_(0.4)Sr_(0.6)FeO_(3-δ) in high-temperature N2O decomposition, methane combustion and ammonia oxidation

摘要

This article is an attempt to elucidate the role of lattice oxygen mobility in catalytic activity of Sr-substituted ferrites at high temperatures. For this goal, three catalysts with close element (La, Sr, Fe) content but different phases and surface compositions: LaSrFeO4(surface)-La_(0.4)Sr_(0.6)FeO3 (LSF-N), La_(0.15)Sr_(0.85)FeO3-La_(0.7)Sr_(0.3)FeO3 (LSF-C) and LaSrFeO4 have been studied in high temperature reactions of N2O decomposition, ammonia oxidation and methane combustion. The kinetics of ~(18)O/~(16)O oxygen exchange have been analyzed at 800 °C and 0.005 atm oxygen partial pressure, which is closely corresponding to the reaction conditions, and the rates of surface oxygen exchange and the coefficient of lattice oxygen diffusion have been evaluated. It allowed us to reveal the direct correlation between the surface exchange rate constant and the rate of N2O decomposition. For NH3 oxidation, evidence of the same order of the samples activity both in surface oxygen exchange and ammonia oxidation reaction was shown. In methane oxidation it was found that activity correlates with the rate of exchange for 20 monolayers of oxygen atoms indicating the growing influence of lattice oxygen mobility. The results show that improvement of catalytic properties can be achieved when synthesizing "LaSrFeO4(surface)-La_(0.4)Sr_(0.6)FeO3" composites. Such composites exhibit increased rate of surface oxygen exchange on retention of high lattice oxygen mobility, which can be attributed to formation of heterostructured interfaces.