An investigation of NO/CO reaction over perovskite-type oxide La0.8Ce0.2B0.4Mn0.6O3 (B = Cu or Ag) catalysts synthesized by reverse microemulsion

The perovskite-type oxides La0.8Ce0.2Cu0.4Mn0.6O3 and La0.8Ce0.2Ag0.4Mn0.6O3 prepared by reverse microemulsion and sol–gel methods (denoted as R and S, respectively), have been investigated on their catalytic performance for the (NO + CO) reaction, and characterized by means of temperature-programmed desorption (TPD), X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). XRD measurements proved the presence of the perovskite phase with a considerable amount of CeO2 phase and the formation of CeO2 phase was restrained with the reverse microemulsion method. TEM investigations revealed that the La0.8Ce0.2Cu0.4Mn0.6O3-R nanoparticles were uniform spheres in shape with diameters ranging from 40 to 50 nm, whereas an aggregation of particles was found for the La0.8Ce0.2Cu0.4Mn0.6O3-S catalyst. The activity of NO reduction with CO decreased in the order of La0.8Ce0.2Cu0.4Mn0.6O3-R > La0.8Ce0.2Cu0.4Mn0.6O3-S > La0.8Ce0.2Ag0.4Mn0.6O3-R > La0.8Ce0.2Ag0.4Mn0.6O3-S. In NO-TPD experiments, the principal desorbed species detected in the effluent was NO with a trace amount of O2 and N2O, suggesting that the non-dissociated adsorption of NO on the surface of the perovskite-type oxides was dominant. The XPS results revealed that Ce4+ and Cu+ was the predominant oxidation state for Ce and Cu components in La0.8Ce0.2Cu0.4Mn0.6O3 and La0.8Ce0.2Ag0.4Mn0.6O3 catalysts. The existence of Cu+ ions and its redox reaction (Cu+ ↔ Cu2+) would benefit the NO adsorption and reduction by CO.