银/氧化铝催化乙醇选择性还原氮氧化物微观结构与构效关系研究

Oxides of nitrogen (NOx) in the atmosphere, as key precursory pollutants, induce the formation of haze. Nowadays, catalytic purification of NOx emission from vehicle exhausts, particularly emission from diesel engines, is one of the hot topics in environmental catalysis, and it is also the top urgent target of air pollution control in China. In this project, Ag/Al2O3-ethanol system will be employed for the selective catalytic reduction of NOx. By careful characterization and calculation of the intrinsic properties such as crystalline planes of support exposed at the surface, distribution and chemical species of silver, and bonding state of Ag-Al, microstructure models of Ag/Al2O3 focused on the interface of active component with support will be drawn. On these models, the roles of layer structure and interlayered OH groups presented in boehmite in the confining and anchoring of Ag species will be investigated. The bonding feature of key and reactive intermediates produced during the HC-SCR process on the surface of catalysts will be identified. With this in mind, more accurate knowledge about the structure-activity relationship of Ag/Al2O3-ethanol system for NOx reduction, and the water- and sulfur-tolerance would be achieved. Also, our result may provide a guideline for designing catalysts with high performance and for developing an ideal HC-SCR system using on-board fuel as reductant for the reduction of NOx emissions from diesel engines in the future.

氮氧化物（NOx）是灰霾形成的重要前体污染物。控制以柴油车为代表的机动车尾气NOx排放是当今环境催化领域的研究热点与我国大气污染治理的迫切需求。本项目以银/氧化铝（Ag/Al2O3）催化乙醇选择性还原NOx-这一高效的组合体系为研究对象，通过对载体暴露晶面、Ag的存在形态、Ag-Al键合状态的精确表征与量化模拟，构建以活性组分-载体界面为核心的Ag/Al2O3微观结构模型；探讨拟薄水铝石层状结构及层间羟基对Ag的限域与锚定；研究关键反应中间体的表面键合特征，获取对Ag/Al2O3催化乙醇选择性还原NOx构效关系、抗水耐硫性能更准确的认知；并以此指导高性能催化剂的设计，为实现以车载油品为还原剂来源的未来理想HC-SCR技术提供指导。

柴油车尾气NOx排放污染是造成大气灰霾、光化学烟雾的重要原因。与氨选择性催化还原NOx技术（NH3-SCR）相比，以车载柴油为还原剂来源的碳氢选择性催化还原NOx（HC-SCR）可免除尿素添加基础设施布建、简化后处理系统。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。本研究以银/氧化铝（Ag/Al2O3）催化乙醇选择性还原NOx—这一高效的组合体系为研究对象，通过对活性组分银的存在形态、活性组分键合特性等内在属性的实验表征与量化模拟，建立了Ag/Al2O3催化剂的微观结构模型，从原子层面揭示Ag+锚定于γ-Al2O3 (110)面AlIII位形成了Ag-O-Altetra结构体，该结构中Ag、O、Al三者之间的轨道融合作用显著降低了能隙，是Ag/Al2O3催化剂上HC-SCR的活性中心。确认了乙醇-SCR反应过程中Ag-O-Altetra结构体上反应物（CH3CH2OH）及关键中间体（CH2=CHO-、-NCO）被活化的电子转移机制，提出了HC-SCR的表面反应机理。以同步辐射真空紫外-光电离质谱技术（VUV−PIMS）研究了Ag/Al2O3催化乙醇部分氧化及其还原NOx的过程，发现了烯醇式自由基(vinyloxy radical)，提出了乙醇-SCR中的气-固反应耦合的反应途径。发现银的负载量显著影响有水条件下Ag/Al2O3的H2-C3H6-SCR活性；在2wt% Ag/Al2O3上，水的存在提高了低温条件下NOx的净化效率。原位红外、化学反应动力学及量化模拟研究表明，水的存在抑制了丙烯部分氧化过程中非活性产物甲酸盐的形成，为活性中间体如烯醇式物种的形成及随后的反应提供更多的位点，提升了低温条件下NOx的净化效率。基于载体氧化铝表面基团对活性组分银的锚定作用的认识，实现了Ag/Al2O3催化剂的制备方法优化。.基于上述研究成果，发表SCI论文10篇，申请并授权发明专利1项。