【作者】 尚建程；

【导师】 沈美庆；

【作者基本信息】 天津大学 ， 环境化学工程， 2008， 硕士

【摘要】 随着汽车尾气污染的日益严重与汽车排放法规的日益严格,对三效催化剂（TWCs）性能提出愈加苛刻的要求。面对复杂的汽车工况运行情况,优良的TWCs在具有高催化转化率同时还应具备宽的空燃比工作窗口。本文针对Pd/Ce_0.67Zr_0.33-Al₂O₃三效催化剂体系,考察了高温水热老化、水蒸气及碱土金属掺杂改性对空燃比窗口特性的影响。采用柠檬酸溶胶-凝胶法制备了碱土金属掺杂的Pd/M-Ce_0.67Zr_0.33-Al₂O₃催化剂（M=Ca、Sr、Ba）,考察了改性催化剂的空燃比窗口特性及动态储放氧性能（OSC）,通过XRD、BET等表征手段探寻引起催化剂活性变化的原因。研究表明:采用溶胶-凝胶法制备的Pd/Ce_0.67Zr_0.33-Al₂O₃催化剂,结晶度差,晶粒较小,具有较好的热稳定性。5%水蒸气气氛下,1050℃水热老化10 h后铈锆固溶体（CZ）未发生分相,催化剂的表面和体相结构得到修饰,空燃比窗口保持了0.125的宽度。反应气氛中存在水蒸气,促进了水煤气变化反应和蒸汽重整反应的进行,进一步扩宽空燃比窗口。碱土金属掺杂改性后,对催化剂结构与性能产生较大影响:①Ca掺杂进入氧化铝晶格中,虽然抑制了氧化铝的烧结,但对拓宽空燃比窗口作用不大;②Sr掺杂同时进入氧化铝和铈锆固溶体晶格中,提高了CO的转化性能以及贫燃时的NO_x还原性能,使空燃比窗口向贫燃方向移动,3%的Sr掺杂量具有较优的空燃比窗口特性;③Ba掺杂影响铈锆固溶体结构,提高了其高温稳定性,并大幅提高贫燃时NO_x的转化率,拓宽了空燃比窗口。催化剂的空燃比窗口与催化剂的比表面积大小无直接关联,主要受催化剂OSC性能的影响。催化剂OSC性能越好,空燃比窗口越宽。更多还原

【Abstract】 Increasing strict regulations for automotive exhaust emission control inevitably demand advanced technologies in three-way catalysts （TWC）. The complexity of vehicle operation conditions not only requires high catalytic efficiency of TWCs at stoichiometric air-fuel ratio, but also needs being compatible for application under wider air-fuel ratios. This thesis aims to investigate the doping effect of alkaline earth metals （Ca, Sr, Ba）, steam in net reaction and hydrothermal ageing for model Pd/Ce_0.67Zr_0.33-Al₂O₃ TWCs.Alkaline earth metals doped Pd/MCe_0.67Zr_0.33O₂-Al₂O₃ （M=Ca, Sr, Ba） were synthesized by a citric acid sol-gel method. TWC, dynamic oxygen storage capability （OSC） tests were performed to evaluate the catalytic redox activities. Contributions from texture modifications were obtained from XRD and BET analysis.Research result reveals that all as prepared samples maintained as fine particles with less crystallization and desirable thermal stability. Due to the optimized bulk and surface texture, phase separation did not take place for ceria-zirconia （CZ） solid solutions after hydrothermal ageing at 1050℃for 10 h, in conjecture with the unchanged 0.125λ-windows’width. Injection of steam in the TWC operating atmosphere promoted the water gas shift （WGS） reaction, and therefore facilitating widen theλ-windows to further extent. Doped alkaline earth metals profoundly influence the catalysts’texture and activity in discrepant ways.①Ca dopants entered the lattice of alumina and depressed the sintering of the latter, without significant effects for the width ofλ-window;②Besides entering alumina lattice, Sr dopants also worked for the lattice of CZ, fueling CO and NOx conversion in lean condition. It is estimated that 3% doped Sr has the optimized effect for widenλ-windows;③Ba dopants affected the structure of CZ in elevating thermal stability and promoting NOx conversion in lean conditions, thus broadening theλ-windows.Width ofλ-windows is of less correlation with the surface areas of TWCs. Instead, higher OSC activity of TWCs is of critical and positive role for widening theλ-windows.更多还原