Preparation And Property Of Ce-based Catalysts For Simultaneously Catalytic Removing NOx And Diesel Soot

Incresing attention has been paid to the air deterioration caused by massive vehicles, therefore it is urgent to find a optimized solution to alleviating the problem. However, NOx and particulate matters(PM), the major pollutants of diesel cars emissions, are of the trade-off relationship, which indicates the restrain of one pollutant will lead to the boom for the other one. It is necessary to introduce post process system in order to meet the regulation due to the limitation of in-engine purification.Ce-based catalysts, prepared by citric acid complex method, were evaluated by the thermogravimetry analysis and temperature programmed reaction and characterized by BET, XRD, TEM, H2-TPR, Soot-TPR and XPS.The Ce1-xLaxO2 solid solution catalysts, prepared utilizing citric acid complex method under different calcination temperature, were studied. It was found that La3+ entered into the CeO2 lattice forming the Ce1-xLaxO2 solid solution. Surface area was a determinant for the reaction. Moreover, the grain size of CeO2 could be significantly restrained by doping with La with the variation of redox properties; higher calcination temperature showed a negative effect on catalytic soot oxidation; the enhanced catalytic activity was acquired under the the gas flow composed of 5% O2 and 2000 ppm NO, which implied the reduction of NOx being in favor of the oxidation of soot. CeLa0.05 was a promising candidate, with the initial temperature at 308 oC.CeO2 doped with transition metals(Co, Fe, Mn, Cu) complex oxides, which contributed to the activity of the simultaneous removal of soot and NOx, were investigated. It was observed that cobalt was dispersed on the surface of CeO2 in the form of Co3O4. The interaction between Cobalt and CeO2 gave rise to the mutual transformation for the metal ions valence, and thus the improvement of redox ability.The improved performance was achieved over optimized Ce-Co complexes oxides catalyst doped by lanthanum. The experiments revealed that a majority of cobalt compounds were dispersed on the surface of Ce-La solid solution in the form of oxides. The contents of Ce-Co complex oxides shrinked after modified by lanthanum, which resulted in the formation of trace amount of LaCo O3, which in turn contributed to increasing the oxygen cavity and thus the catalytic activity. Co0.1/CeLa0.05 showed the best catalytic performance in simultaneous removal of both soot and NOx, with T10=289 oC and T50=357 oC in air; while under the gas flow composed of 5% O2 and 2000 ppm NO, T10 and T50 were 269 oC and 301 oC respectively, with 41.4% N2 yield and 95.1% N2 selectivity.