Research On The Behavior Of Three-way Catalysts For Automotive Exhaust With Ceria-Zirconium-lanthanum Complex Oxide And Catalystic Mechanism

The addition of ceria-zirconium-lanthanum complex oxide on catalyst were studied experimentally. The results are as follows,after calcined at 600 癈 , ceria-zirconium-lanthanum complex oxide which is made from Ce0.5~0.65Zr0.4~0.3Lao.i~0.05O2.xls formed according to XRD.The additon methods of Ce-Zr-La complex oxide makes use of doping-precipation, because it can improve more significantly the behaivor of the automotive catalysts including activity and thermal durability than doping, doping-coating or precipitation-mixation. The best additional loading of Ce-Zr-La complex oxide is 8~10%(wt of the total supporter).After the catalyst with Ce-Zr-La complex oxide aged 3h at 830~840癈, its BET surface area decreases 0.14m2/g. and its three-way activity (conversion efficiency of CO, HC and NOx) decreases by 0%,4.3% and 2.7% at 450 "C by comparison of the same fresh catalyst. The addition of Palladium may increase oxidation activity of CuO-CeO2-Mn2O3/y-Al2O3 for CO and HC, which has little contribution to reduction for NOx.. Under the condition of 320癈, CO and HC conversion efficiencys increase by 6.1% and 36.1%.At last, catalystic reaction mechanism on CuO-CeOrMn2O3-Pd/y-Al2O3 with Ce-Zr-La complex oxide is also investigated. Experimental results show that three way activity is higher when oxidation-reduction rate (R) ranges from 0.81 to 0.95, R is equal to 0.9, 53.7% is the best conversion efficiency for NO. NO2 is easier to be reduced N2 than NO. The reaction between CO or HC is very slow beyond 280"C. However, a part of NO is easy to be oxidized NO2 at low temperature.,In addition, the reaction between CO or HC and NO or N02 may take place. At the same time, the wate-gas shift and steam reforming reactions happen. Above 280 癈, the oxidation reaction of CO and HC start and become rapid as the temperature increases. NO is difficult to become NO2 at the prence of O2 in contrast to the former, and NO can directly reacts with CO or HC. But the wate-gas shift and steam reforming reactions are greatly limited. Therefor, the reaction rate of NO decreases.