Pd(111)与Pt(111)上NO氧化的第一性原理研究  

First Principles Study of NO Oxidation on Pd(111)and Pt(111)

作　　者：李志军[1] 曹飞[1] 王学豹 李世龙 张时杰 李振国[3] Li Zhijun;Cao Fei;Wang Xuebao;Li Shilong;Zhang Shijie;Li Zhenguo(State Key Laboratory of Engines(Tianjin University),Tianjin 300072,China;China North Engine Research Institute,Tianjin 300400,China;China Automotive Technology&Research Center Co.,Ltd.,Tianjin 300300,China)

机构地区：[1]先进内燃动力全国重点实验室(天津大学),天津300072 [2]中国北方发动机研究所,天津300400 [3]中国汽车技术研究中心有限公司,天津300300

出　　处：《天津大学学报（自然科学与工程技术版）》2024年第6期588-594,共7页Journal of Tianjin University：Science and Technology

基　　金：国家自然科学基金资助项目(51976136,51576140);移动源排放控制技术国家工程实验室开放基金资助项目(NELMS2019-B01,NELMS2017A02);清华大学汽车安全与节能国家重点实验室开放基金资助项目(KF1818).

摘　　要：随着排放法规的日益严格,发动机的氮氧化物(NO_(x))后处理已成为当今研究的重点问题.针对目前可有效降低稀燃汽油机NO_(x)的稀燃氮氧化物捕集器中铂(Pt)和钯(Pd)两种贵金属之间的替换问题,进行了密度泛函理论(density functional theory,DFT)计算研究.首先,对一氧化氮(NO)、氧气(O_(2))、二氧化氮(NO_(2))在两种催化剂(111)表面的吸附进行了研究,之后,在两催化剂表面对比研究了氧化过程中涉及的O_(2)解离与NO氧化两反应过程,揭示了NO在Pd与Pt催化剂上的氧化机理.结果显示:3种物质在催化剂表面的吸附强度为NO>O_(2)>NO_(2).氧覆盖度将会改变氮氧化物的最佳吸附构型,随着表面氧原子的增加NO会由三重空位式吸附转变为顶点吸附,NO_(2)会由μ-N,O-亚硝基吸附转变为硝基吸附.在O_(2)解离过程中Pt的催化能力优于Pd,但是两者对NO氧化的催化能力接近.在Pd和Pt表面反应限速步骤都是O_(2)的解离,Pd对O_(2)较弱的解离能力导致了其NO的转化效率低于Pt.氧覆盖度对氧化过程存在影响,通过电子结构分析发现,氧覆盖度的提升使催化剂与吸附物质之间的吸附能下降,这导致了反应由吸热变为放热,使催化可以自发进行.反应生成的NO_(2)需要1.00 eV以上的能量完成脱附,这在原子层面解释了NO_(2)对NO氧化反应的抑制作用.With emission regulations becoming increasingly stringent,the focus of research has turned to the aftertreatment of nitrogen oxide(NO_(x))from engines.In this work,density functional theory(DFT)was used to investigate the potential replacement for platinum(Pt)and palladium(Pd)in a lean-burn nitrogen oxide trap,which can effectively reduce NO_(x) emitted from lean-burn gasoline engines.First,the adsorption of nitric oxide(NO),oxygen(O_(2)),and nitrogen dioxide(NO_(2))on the(111)surfaces of the two catalysts was explored.Further,two reaction processes involved in the oxidation process,O_(2) dissociation and NO oxidation,were compared on the surface of the two catalysts.The NO oxidation mechanism on the Pd and Pt catalysts was obtained.The results show that the adsorption strength of the three substances on the catalyst surface is in the following order:NO>O_(2)>NO_(2).Oxygen coverage changes the optimal adsorption configuration of NO_(x).As the concentration of surface oxygen atoms increases,NO changes from face-centered cubic adsorption to top-point adsorption,and NO_(2) changes from μ-N,Onitrito adsorption to nitro adsorption.Pt has a better catalytic capacity than Pd for O_(2) dissociation,but its catalytic capacity for NO oxidation is similar to that of Pd.Furthermore,O_(2) dissociation is the rate-limiting step of the reaction on the Pd and Pt surfaces.The weak dissociation ability of Pd for O_(2) results in its lower NO conversion efficiency,compared to Pt.The Oxygen coverage has an influence on the oxidation process.Electronic structure analysis reveals that increasing Oxygen coverage decreases the adsorption energy between the catalyst and adsorbent,resulting in the reaction becoming exothermic;hence,the catalysis proceeds spontaneously.The NO_(2) generated by the reaction re-quires more than 1.00 eV to complete desorption,which explains the inhibitory effect of NO_(2) on NO oxidation at the atomic level.

关 键 词：稀燃氮氧化物捕集器 第一性原理 铂族催化剂 一氧化氮氧化 

分 类 号：TK411[动力工程及工程热物理—动力机械及工程]