整体式Pd/La_2O_3-Al_2O_3和Pd/CeO_2-ZrO_2-Y_2O_3催化剂上汽油车尾气净化性能的比较

Comparison of Automotive Exhaust Purification Performance of Monolith Catalysts Pd/La_2O_3-Al_2O_3 and Pd/CeO_2-ZrO_2-Y_2O_3

采用共沉淀法制备了耐高温高比表面积的La2O3-Al2O3(LA)材料和CeO2-ZrO2-Y2O3(CZY)储氧材料,并用浸渍法制备了整体式Pd/LA和Pd/CZY汽油车尾气净化三效催化剂,考察了它们的三效催化性能和空燃比性能,并单独通过水煤气变换和CO氧化反应性能的考察,探讨了两种催化剂空燃比窗口扩大的原因.结果表明,Pd/CZY催化剂三效窗口明显较宽,且催化氧化CO的性能明显更优;对于CO+NO反应,Pd/CZY催化剂的活性较高.当反应中逐步通入O2后,抑制了该反应的进行,但CO氧化的转化率升高,而NO转化率降低,直至CO+NO反应完全被抑制,表明CO氧化反应对于抑制催化剂在NO贫燃方向的窗口具有一定的作用.另外,Pd/CZY催化剂上对于水煤气变换反应性能明显优于Pd/LA催化剂,在一定温度下逐步通入O2后,不会抑制水煤气变换反应的发生;当逐步通入NO时,可以促进水煤气变换反应的进行,表明Pd/CZY催化剂在富燃时对扩展CO转化窗口的性能明显优于Pd/LA催化剂.

Two kinds of support materials,the thermal-stability material La2O3-Al2O3（LA） and oxygen storage material CeO2-ZrO2-Y2O3（CZY）,were prepared by co-precipitation.Pd/LA and Pd/CZY catalysts were prepared by impregnation and they were further fabricated as three-way catalysts in a monolith form.The Pd/LA and Pd/CZY three-way catalysts thus prepared were evaluated with a simulated automobile exhaust in terms of the relationships of three way performance with the air-to-fuel ratio（A/F） window and with temperatures.The results indicated that the A/F window and the three-way activity of the Pd/CZY catalyst were broader and higher than those of the Pd/LA catalyst.To investigate in more details,several reactions that involved CO in exhaust purification process such as CO oxidation,water-gas shift（WGS） reaction,and NO reduction by CO were examined over Pd/LA and Pd/CZY catalysts.These preliminary studies revealed that the advantages of the Pd/CZY catalyst are mainly from the unique properties of the CeO2 oxygen storage material.Furthermore,it was found that addition of either O2 or NO in reactant gases is favorable for the WGS reaction,which gives some clues for developing an advanced three-way purification process.