基于理论计算结合原位红外光谱的铈基低温脱硝催化剂硫中毒机理及结构-抗硫性能关系研究

Improving the ability of low-temperature sulfur-poisoning resistance in the selective catalytic reduction of NOx with NH3 (NH3-SCR) over ceria-based de-NOx catalysts is one of the important challenges in environmental catalysis. The lack of deep insights into the sulfur-poisoning mechanism and structure-performance relationship seriously hinders the rational design and development of ceria-based low-temperature de-NOx catalysts with high sulfur-poisoning resistance ability. In this project, choosing CeO2-supported highly dispersed TiO2 catalysts as the research system, combining theoretical calculation and in-situ DRIFT methods, the structure-tuning mechanism to improve the sulfur-poisoning resistance ability at the atomic scale will be explored. Firstly, the reaction mechanism and sulfur-poisoning mechanism will be systematically investigated, revealing the structure of active sites and the catalytic origin of the synergy effect between CeO2 and TiO2, clarifying the detailed steps in the sulfur-poisoning process; then, the effect of surface structure tuning and doping on the catalytic activity and sulfur-poisoning will be investigated, revealing the relationship between the geometric and electronic structures and the activity as well as the ability of sulfur-poisoning resistance over ceria-based catalysts, summarizing the tuning mechanism which can improve the catalytic activity of the active sites and simultaneously inhibit SO2 adsorption at the active sites, achieving the separation of catalytic active sites and SO2 adsorption sites. The achievements in this project will provide a scientific guidance for the rational development of ceria-based low-temperature de-NOx catalysts with high sulfur-poisoning resistance ability.

如何提高铈基氨选择性催化还原（NH3-SCR）脱硝催化剂的低温抗硫性能是环境催化领域的重要挑战之一。对硫中毒机理和构效关系缺乏深入认识严重阻碍了高抗硫性铈基低温脱硝催化剂的设计与开发。本项目针对CeO2负载高分散TiO2催化剂体系，采用理论计算结合原位红外光谱的方法，从原子层面上探索能够提高抗硫中毒性能的结构调控机制。首先系统研究反应机理和硫中毒机理，揭示活性位结构以及CeO2-TiO2协同作用影响催化性能的本质，明确硫中毒的详细步骤；在此基础上，研究催化剂的表面结构调变与掺杂改性对催化活性与硫中毒的影响，阐明铈基催化剂的几何结构与电子结构影响活性与抗硫中毒性能的构效关系，归纳出即能提升活性位点的催化活性而同时又能抑制SO2在活性位点吸附的调控机制，达到分离催化活性位与SO2吸附位的目标。研究结果可为开发高抗硫性铈基低温脱硝催化剂提供科学指导。

工业废气和机动车尾气排放的氮氧化物（NOx）是大气污染物细颗粒物和臭氧的主要前体物之一，还可产生光化学烟雾和硝酸型酸雨，严重危害人体健康和生态环境。研发高效氮氧化物催化净化（脱硝）催化剂是实现氮氧化物减排的关键与核心。本项目采用“DFT理论计算指导催化剂结构设计”的研究手段，从原子水平上精确调控稀土二氧化铈的表面结构，获得了高效的铈基低温脱硝催化剂，主要研究内容与结果如下：.1、设计与制备出高效Ce-Ti催化剂，该催化剂在低温条件下（200-250℃）具有优异的催化活性，转化率在90%以上，在200ppm二氧化硫的条件下，转化率仍可达到90%以上。构筑的Ce-Cr催化剂具有高抗硫中毒性能，在低温、200ppm二氧化硫存在的情况下，转化率可达到100%，并能够长时间保持稳定。.2、揭示活性位微观结构、反应机理与硫中毒机理，发现临近掺杂元素的Ce位点及次临近掺杂元素的O位点是NH3-SCR催化活性位，NH3-SCR反应主要遵循Eley-Rideal机理。决定活性的本质参数是EH/ENH3和Evac值。.3、阐明结构调变影响催化活性与抗硫性能的作用机制，固溶体结构的CeTiOx催化剂具有优异的本征活性和抗硫中毒性能，这与其表面适中的氧化还原性能和酸性有关，同时，固溶体中Ti位点特殊的几何结构和电子结构使其扮演着SO2捕获位点的作用，从而有效保护催化活性位点；而CeO2-TiO2界面的Ce-O-Ce结构被SO2硫化后会阻止NH3的解离，同时界面Ce-O-Ti结构存在着NH3与SO2的竞争吸附问题。.4、揭示掺杂改性影响催化活性与抗硫性能的作用机制，通过对Ce-Ti、Ce-W、Ce-Cr等不同类型掺杂改性的铈基催化剂分析，发现Ce基NH3-SCR催化剂的催化性能极大地依赖掺杂元素，这是由于不同的掺杂元素呈现出不同的表面配位结构和配位环境，四配位、四面体M-O构型是高活性与高抗硫性的关键。.本项目对铈基NH3-SCR催化剂的活性位结构、催化作用机制、硫中毒机理提供了原子层面上的认识，并揭示了几何结构和电子结构调变影响活性与抗硫性能的构效关系，这将为理性设计高效稀土铈基低温脱硝催化剂提供科学指导。.