The Synthesis Of Lanthanum Cobalt Perovskite Type-oxides Catalysts And Its Catalytic Properties In Simultaneous Removal Of NOx And Soot

A number of catalysts based on the lanthanum cobaltite perovskite type oxides were prepared by solution combustion synthesis or citric acid complexation. The catalysts were characterized using XRD, FT-IR, H2-TPR, XPS, BET, SEM-EDS and TEM. The catalytic activities simultaneously removed soot and NOx were evaluated using a technique of temperature programmed reaction (TPR) under the modeled diesel engine exhaust circumstance.Firstly, the La1-xKxCoO3 (x=0～0.5) perovskite-type oxides were prepared by solution combustion synthesis. The results showed that all prepared catalysts possessed ABO3 perovskite-type structures with porous sponge-like structure, corresponding to a rhombohedral system. For the La1-xKxCoO3 catalysts, since the partial substitution of K for La at A-site resulted in the increase of oxygen vacancy and Co3+-Co4+ system, it enhanced the catalytic performance. La0.7K0.3CoO3 catalyst with the highest catalytic activity was observed, and the maximum NO conversion into N2 and the ignition temperature of soot were 27.5%and 262°C, respectively.Secondly, a number of nan-perovskite catalysts LaCo1-xPdxO3(x=0～0.03) were prepared via solution combustion synthesis. The noble metal Pd in the form of Pd3+ or Pd4+ was successfully deposited onto the LaCoO3 perovskite lattices, leading to improve the catalytic performance significantly . The maximum NO conversion into N2 and the temperature of were 32.8% and 265°C, respectively.Thirdly, the novel La1-xMexCo1-yPdyO3(Me=K, Sr, Ce x = 0,0.2 y=0,0.05) catalysts with ABO3-type structure were prepared using the citric acid complexation. For the LaCoO3 catalyst, the partial substitution of K or Sr at A-site enhancing the catalytic performance was found, while no improve the catalytic activity from the Ce-substituted catalysts was observed. Moreover, the catalytic activities of all the Pd-substituted catalyst further increased and La0.8Sr0.2Co0.95Pd0.05O3 showed the highest activity. The maximum conversion of nitrogen oxide to N2 and the ignition temperature were 31.6% and 258°C, respectively.Finally, Effects of reaction conditions on catalytic performance, including concentrations of O2 and total flow rate, were investigated over three catalysts. the mechanisms were proposed based on both our results and other work. The carbon particulate plays an important role in the reduction of NO, and NO, it also affected the oxidation of carbon particulate. The ignition temperature decreased with increasing O2 concentration. The maximum NO conversion into N2 catalyst increased in range from 1% to 5% using a La0.8Sr0.2Co0.95Pd0.05O3 catalyst. The total gas flow rate did less influence on the ignition temperature of soot. The La0.8Sr0.2Co0.95Pd0.05O3 catalyst showed better performance over the total gas flow rate range of 25 mL/min～50 mL/min.