中文摘要：

机动车污染物排放是我国大气复合污染形成的重要原因之一.尽管柴油车在我国机动车保有量中所占比例不到20%,但其排放的颗粒污染物（PM）和氮氧化物（NOx）分担率均超过60%.因此,控制柴油车尾气排放成为我国亟待解决的大气污染问题.目前,氨选择性催化还原NOx技术（NH3-SCR）已规模化应用于柴油车污染排放控制,出于安全性考虑,以尿素水溶液作为氨的来源.但NH3-SCR技术应用于柴油车尾气净化存在如下缺点：需要布建庞大的尿素添加基础设施、后处理系统复杂等.与此相反,以车载燃油为还原剂来源的HC-SCR技术可有效规避上述难题,展现了较好的应用前景.但是,直接以柴油为还原剂时,HC-SCR对NOx净化的效率还难以满足日益严格的排放法规的要求,因此需要深入研究HC选择性还原NOx的微观机制与构效关系,并以此为指导,发展以车载燃料为还原剂来源的高效净化NOx的新原理和新方法.已有的研究表明,银/氧化铝（Ag/Al2O3）具有优异的催化乙醇选择性还原NOx的能力,是最有希望应用于柴油车尾气NOx净化的催化剂-还原剂组合体系.鉴于此,本论文以Ag/Al2O3催化剂上乙醇-SCR反应为研究对象,以密度泛函理论计算方法（DFT）搭建了Ag/Al2O3催化剂的理论模型,考察了反应物乙醇（CH3CH2OH）、关键中间体（烯醇式物种CH2=CHO-和-NCO）在Ag/Al2O3催化剂上的吸附特征,采用电子态密度分析（DOS）研究了以上物种被活化的电子机制,以期甄别Ag/Al2O3催化乙醇选择性还原NOx的活性位结构,为高性能的HC-SCR催化剂设计提供指导.依据化学态的不同,Ag/Al2O3催化剂上活性组分银可分为：高度分散的离子态（Ag＋、在催化剂表面以Ag-O形式存在）、部分氧化团簇（Agn^δ＋）和金属颗粒银（Agn^0）,其中氧化态的银是催化乙醇选择性还原NOx的活性组分.Al2O3载体的主要暴露晶面为（110）和（100）,在上?

英文摘要：

The adsorption of ethanol and important intermediates onto Ag/Al2O3 catalyst employed in the selective catalytic reduction of NOx by ethanol was simulated by density functional theory. Consid-ering the interaction between Ag metal and Al2O3 support, typical Ag–O–Al entities, i.e., Ag–O–Altetra and Ag–O–Alocta, （tetra =tetrahedral and octa= octahedral refer to the coordination sites of Al）, were selected as potential adsorption sites on the surface of the catalyst. Ethanol, and enolic and isocyanate species were preferentially adsorbed and activated by Ag–O–Altetra entities rather than by Ag–O–Alocta entities. The strong Lewis acidity of Altetra in the Ag–O–Altetra entity was very im-portant, enabling the entity to accept an electron via forward donation from either the C–Oσbond in ethanol or the N–Cσbond in the-NCO species. Moreover, the hybridization of the Ag and Al orbitals was critical for electron back donation from the Ag–O–Altetra entity to the C–Cπbond in the enolic species or N–Cπbond in the-NCO species. The significant activation of the N–C bond in-NCO on the Ag–O–Altetra sites facilitated cleavage of-NCO to form N2. Thus, we can conclude that the acidity of the Al site and the interaction between Ag and Al play key roles in the selective cata-lytic reduction of NOx by ethanol over Ag/Al2O3.