Zr的添加对稀燃天然气汽车尾气净化催化剂Pd-Pt/Al_2O_3性能的影响（英文）

Effects of Zr Addition on the Performance of the Pd-Pt/Al_2O_3 Catalyst for Lean-Burn Natural Gas Vehicle Exhaust Purification

Pd-Pt双金属基甲烷氧化催化剂的催化活性、抗水热老化性和耐硫性在一个通有模拟稀燃天然气汽车尾气成分的固定床反应器中进行检测.研究发现Zr掺杂的Pd-Pt/Al2O3(Pd-Pt/Zrx Al(1–x)O(3+x)/2)提高了催化的催化活性、抗水热老化性和耐硫性.以共沉淀法制备Zr:Al的摩尔比分别为0:1、0.25:0.75、0.5:0.5、0.75:0.25和1:0的材料为载体材料.双金属催化剂的活性组分分别为1.5%(w,质量分数)的Pd和0.3%(w)的Pt,活性组分Pd、Pt通过共浸渍的方法浸渍到以上载体材料上制备得到一系列整体式催化剂.分别采用低温N2吸脱附、X射线衍射(XRD)、H2程序升温还原(H2-TPR)、O2程序升温氧化(O2-TPD)及X射线光电子能谱对制备的催化剂进行表征.结果显示Zr的加入使催化剂的载体材料结晶度提高,活性组分的分散度也得到了相应的提高.同时二价Pd物种与周围电子密度分别增加.相比于Pd-Pt/Al2O3和Pd-Pt/ZrO2催化剂,在不同条件预处理后,Zr的添加对催化剂的性能有明显的提高,其中催化剂Pd-Pt/Zr0.5Al0.5O1.75展现了最好的催化活性、抗水热老化性以及耐硫性.

The catalytic activity, hydrothermal aging resistance, and sulfur tolerance of a Pd-Pt-based methane oxidation catalyst were evaluated in a fixed fluidized bed reactor containing simulated lean-burn natural gas vehicle exhaust gases. Zirconium-doped Pd-Pt/Al2O3（Pd-Pt/Zrx Al（1–x）O（3＋x）/2） was found to significantly improve the catalytic activity, hydrothermal aging resistance, and sulfur tolerance. Zr-modified alumina supports were prepared by co-precipitation with molar ratios of Zr to Al of 0 ： 1, 0.25 ： 0.75, 0.5 ：0.5, 0.75 ： 0.25, and 1 ： 0. The Pd-Pt bimetallic catalysts containing 1.5%（w, mass fraction） Pd and 0.3%（w） Pt supported on the above-modified composite supports were prepared by the co-impregnating method.The catalysts were characterized by N2 adsorption/desorption, X-ray diffraction（XRD）, H2 temperatureprogrammed reduction（H2-TPR）, O2 temperature-programmed desorption, and X-ray photoelectron spectroscopy（XPS）. The results show that the crystallinity of the samples, dispersion of the active component, number of Pd2＋ species, and electron density around Pd2＋ species increase after addition of ZrO2 to Al2O3 supports. Compared with the activity results of Pd-Pt/Al2O3 and Pd-Pt/ZrO2 catalysts after different pretreatment conditions, the performance of the catalyst is greatly enhanced by adding ZrO2 in the Al2O3 supports, and Pd-Pt/Zr0.5Al0.5O1.75 shows the best catalytic activity, strongest hydrothermal aging resistance, and highest sulfur tolerance among the investigated catalysts.