载体材料对单Pd三效催化剂性能及催化活性的影响(英文)

Effect of Support Materials on Property and Catalytic Performance of Pd-Only Three-Way Catalyst

采用共沉淀法制备了耐高温高比表面的La2O3-Al2O3(LA)以及铈含量分别为15%、33%和47%的储氧材料Ce O2-Zr O2-La2O3-Al2O3(CZLA)、Ce O2-Zr O2-La2O3+La2O3-Al2O3(CZL+LA)和Ce O2-Zr O2-La2O3(CZL)4类载体材料,并用浸渍法制备了整体式Pd/LA、Pd/CZLA、Pd/CZL+LA和Pd/CZL汽油车尾气净化三效催化剂,考察了载体材料对单Pd三效催化剂的影响。采用低温N2吸附-脱附、H2-程序升温还原(H2-TPR)以及X射线光电子能谱(XPS)对载体材料及催化剂进行了表征,并考察了催化剂的空燃比性能和三效催化性能。结果表明,CZLA有效地结合了铈基和铝基载体材料的优点,表现出了优异的织构性能、热稳定性及还原性能。老化前后,其负载的单Pd三效催化剂在低温还原率、表面元素含量及Pd的电子结合能等性能方面表现出了最小的差异。催化剂活性测试结果表明,Pd/CZLA的三效窗口明显较宽,且拥有最低的起燃温度,尤其经1 000℃老化处理后,其催化活性最高,C3H8、NOx和CO的起燃温度分别为370、257和223℃。可见,相较于其他3种载体材料,CZLA更适合于负载单Pd三效催化剂,从而满足更高标准的三效催化剂的性能要求。

Four kinds of support materials, i.e. a thermally stable material La2O3-Al2O3（LA）, three oxygen storage materials Ce O2-Zr O2-La2O3-Al2O3（CZLA）, Ce O2-Zr O2-La2O3＋La2O3-Al2O3（CZL ＋LA） and Ce O2-Zr O2-La2O3（CZL） with ceria content of 15%, 33% and 47%, respectively, were prepared by co-precipitation. The corresponding Pd-only catalysts Pd/LA, Pd/CZLA, Pd/CZL＋LA and Pd/CZL were obtained by wet-impregnation and further fabricated as three-way catalysts in a monolith form. The support materials were characterized by low temperature nitrogen adsorption-desorption and H2-temperature programmed reduction（H2-TPR）. The catalysts were characterized by H2-TPR and XPS, and were evaluated with a simulated automobile exhaust in terms of the relationships of three way performance with the air/fuel operation window and with temperatures. The results indicate that the support material CZLA integrates the advantages of ceria-based and alumina-based materials effectively thus having superior textural property, thermal stability and reduction property. Additionally, Pd/CZLA catalyst shows little difference in low temperature reducibility, surface elemental distribution and elemental oxidation states before and after aging treatment. As a result, Pd/CZLA exhibits the widest air/fuel operation window and the lowest light-off temperature among the four catalysts, especially after aging treatment, the light-off temperature of C3H8,NOxand CO is 370 ℃, 257 ℃, 223 ℃, respectively. Then material CZLA is the most suitable support for Pd-only three-way catalyst compared with the other three supports.