Experimental and Computational Investigation of Effect of Sr on NO Oxidation and Oxygen Exchange for La1-xSrxCoO3 Perovskite Catalysts

NO oxidation rates over La1-xSrxCoO3 (x = 0-0.3) perovskite catalysts are reported as a function of Sr doping in the absence and presence of NO2 in the feed. Sr substitution is found to increase the rate of oxidation and to diminish the inhibitory influence of NO2. Temperature programmed desorption and isotopic exchange (TPIE) experiments were used to identify surface species and oxygen exchange processes expected to correlate with NO oxidation activity. Oxygen exchange in the LaCoO3 perovskites occurred primarily through a heteroexchange process that was enhanced by doping with Sr. Density functional theory (DFT) calculations were used to further investigate the oxygen exchange processes on (100) facets of undoped and doped LaCoO3. Vacancy formation is predicted to be more facile on CoO2-terminated than LaO-terminated surfaces. The Sr dopant segregates to the LaO-terminated surface and diminishes oxygen bonding consistent with the TPIE results. The results suggest a model in which multiple oxygen species contribute to low- and high-temperature oxygen exchange.