CO Oxidation, NO Decomposition, and NO + CO Reduction over Perovskite-like Oxides La2CuO4 and La2-xSrxCuO4: An MS-TPD Study

Perovskite-like oxides La2CuO4 and LaSrCuO4, prepared by the citrate combustion method, were studied and used as catalysts for CO oxidation, NO decomposition, and NO + CO reduction. The adsorption and desorption behaviors of the gases on catalyst surfaces were well characterized by mass spectrometric-temperature programmed desorption (MS-TPD) measurements. A large NO desorption peak was observed on LaSrCuO4, but only a small one was observed on La2CuO4, suggesting that the Sr addition or the existence of an oxygen vacancy is the necessary condition for NO adsorption. No CO desorption peak was observed on either LaSrCuO4 or La2CuO4, suggesting that the adsorbed CO was totally oxidized to CO2 before elution. The appearance of N2 desorption peak in the NO MS-TPD spectra of LaSrCuO4 (T = 400 (degree) C) indicated that NO dissociation occurs easily and the crucial step of NO decomposition is O2 desorption. The activity of LaSrCuO4 was low for NO decomposition (34.3%, T = 850 (degree) C), but high for CO oxidation (99%, T = 300 (degree) C) and for NO + CO reduction (98.7%, T = 600 (degree) C), suggesting that the desorption of oxygen, or the regeneration of active site, is difficult in NO decomposition but easy in CO oxidation and NO + CO reduction, due to the existence of CO. Finally, the mechanism of NO + CO reduction was investigated according to the ratio XNO/XCO; the variation of the ratio XNO/XCO suggests that the NO + CO reduction has different mechanisms over different catalysts and at different temperatures.