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

Perovskite-like oxides La 2 CuO 4 and LaSrCuO 4, 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 LaSrCuO 4, but only a small one was observed on La 2 CuO 4, 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 LaSrCuO 4 or La 2 CuO 4, suggesting that the adsorbed CO was totally oxidized to CO 2 before elution. The appearance of N 2 desorption peak in the NO MS−TPD spectra of LaSrCuO 4 ( T = 400 °C) indicated that NO dissociation occurs easily and the crucial step of NO decomposition is O 2 desorption. The activity of LaSrCuO 4 was low for NO decomposition (34.3%, T = 850 °C), but high for CO oxidation (99%, T = 300 °C) and for NO + CO reduction (98.7%, T = 600 °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 X NO / X CO; the variation of the ratio X NO / X CO suggests that the NO + CO reduction has different mechanisms over different catalysts and at different temperatures.