基于活性组分微化学状态调控的高性能Rh/CeO_(2)-ZrO_(2)-Al_(2)O_(3)催化剂构筑及三效催化性能

Construction of a Highly Active Rh/CeO_(2)-ZrO_(2)-Al_(2)O_(3) Catalyst Based on Rh Micro-Chemical State Regulation and Its Three-Way Catalytic Activity

近年来,贵金属Pt、Pd、Rh价格不断攀升,提高贵金属利用效率成为未来汽油车三效催化剂的发展趋势之一。本文协同液相还原和气氛热处理技术精细调控贵金属铑(Rh)的微化学状态,以优化低含量Rh基催化剂的催化性能。同时,采用X射线粉末衍射(XRD)、H2-程序升温还原(H2-TPR)、CO化学吸附、X射线光电子能谱(XPS)、CO-漫反射红外(COFTIR)、透射电镜(TEM)和原位漫反射傅里叶变换红外吸收光谱(in situ DRIFTS)等催化剂表征方法,详细研究了Rh微化学状态(价态比例、分散性等)与催化性能之间的关系。活性测试结果表明,通过上述协同方法制备的re-Rh/CeO_(2)-ZrO_(2)-Al_(2)O_(3)-H2(re-Rh/CZA-H2)催化剂表现出最好的催化活性,并且拓宽了空燃比操作窗口,其T90值分别比液相还原法和浸渍法合成的催化剂低30–73℃和51–86℃。此外,通过协同方法制备的催化剂老化后也表现出优异的催化活性和高温热稳定性,其T50和T90值均低于新鲜样品。构效关系结果表明,re-Rh/CZA-H2催化剂优异的催化性能归因于Rh物种具有最佳价态比例和高分散性,从而增加了活性位点的数量。同时,re-Rh/CZA-H2-a催化剂具有相当优异的高温热稳定性,这归因于载体材料的结构稳定性,及活性Rh物种的高含量和高分散,从而暴露出更多的活性位点,促进反应物的吸附和转化。因此,采用本工作提出的协同方法来调整贵金属的微化学状态,可以提高催化剂的催化活性、高温稳定性以及空燃比操作窗口,为设计低负载量Rh基三效催化剂提供一个新思路。

With the increasing number of automobile vehicles,the exhaust emitted poses a severe menace to the environment and human health,necessitating the purification of exhaust pollutants.Meanwhile,the high price of noble metals and their limited supply require a decrease in noble metal loading to reduce the costs of three-way catalysts(TWCs).Therefore,improving the utilization efficiency of noble metals and their catalytic behavior is critical for the development of next-generation TWCs with low noble metal loading.Herein,the Rh micro-chemical state was modulated using the liquid-phase reduction method combined with atmospheric heat treatment to enhance the catalytic behavior of Rh-based catalysts with low Rh loading.The catalyst was characterized using X-ray diffraction(XRD),hydrogen temperature programmed reduction(H2-TPR),CO chemisorption,X-ray photoelectron spectroscopy(XPS),the FTIR spectroscopy of chemisorbed CO(CO-FTIR),transmission electron microscopy(TEM),and in situ diffuse reflectance IR(in-situ DRIFTS)to illustrate the relationship between Rh micro-chemical state(including valence state ratio and dispersion)and catalytic activity.The asprepared catalyst re-Rh/CeO_(2)-ZrO_(2)-Al_(2)O_(3)-H2(re-Rh/CZA-H2)exhibited better catalytic activity and a wider air/fuel ratio(λ)operating window with T90 values 30–73℃ and 51–86℃ lower than those of the catalysts synthesized by liquid-phase reduction and traditional impregnation method,respectively.In addition,aged samples prepared by the combined scheme also exhibited excellent activity and stability,where the T50 and T90 values were lower than the fresh catalyst.Structureactivity relationship results demonstrated that the better catalytic activity of re-Rh/CZA-H2 could be attributed to the optimal valence state ratio and highly dispersed Rh species,which increased the number of effective active sites.The considerable stability was attributed to the stable structure of the CeO_(2)-ZrO_(2)-Al_(2)O_(3)(CZA)support,improved dispersion,and the high contents of active Rh species,which exposed more active sites to promote reactant conversion.In addition,the synergistic effect between the metallic Rh and oxygen vacancies could facilitate the anchoring of Rh nanoparticles to inhibit Rh sintering.Therefore,adjusting the micro-chemical state of noble metals by the combinatorial scheme developed herein provides a novel route for improving the catalytic activity,high-temperature stability,and air/fuel operating window of these catalysts.