Promotion Effects of Cesium on Perovskite Oxides for Catalytic Soot Combustion

Abstract

The cesium-promoted LaCoO3 perovskite-type catalysts were synthesized for catalytic soot combustion. The cesium promoter was introduced into the perovskite system via two different ways with the same Cs loading: one is Cs doping (La0.8Cs0.2CoO3), and the other is Cs supporting (Cs/LaCoO3). The physicochemical properties of the catalysts were characterized by XRD, N2-sorption, SEM, EDS, H2-TPR, NO oxidation and NOx sorption techniques. For Cs-supported sample, the promotion effect on the redox properties of transition metal has been observed. The catalytic NO oxidation activity on Cs-supported sample was higher than that on Cs-doped sample due to the improved reducibility. Under O2 atmospheres, the two kinds of Cs-containing catalysts exhibited similar ignition activities under tight conditions with soot ignition temperature decreased to about 350 °C, which can be related to the enhanced oxygen mobility and the improved contact between soot and catalysts. In the presence of NOx, the superior soot oxidation activity on Cs-supported catalyst was related to its higher NO2 productivity, larger NO2 consumption and more stored nitrates accessible in soot oxidation process. Thus, the different ways to introduce cesium have different impacts on the properties and activities of the perovskite catalysts. Cesium surface promotion is much more effective than the bulk promotion in soot oxidation over LaCoO3 perovskite catalysts.