铈基氨选择性催化还原氮氧化物催化剂的结构调控及SO2中毒机理

The selective catalytic reduction (SCR) of nitrogen oxides (NOx) with ammonia is one of effective technologies for abating NOx in the flue gas from stationary sources. However, there are some problems，including high toxicity of vanadia, high activity for oxidation of SO2 and high reaction temperature, for the traditional vanadium-titanium based SCR catalysts. Ceria seems to be a promising environment-friendly catalyst for the SCR of NO with ammonia due to its unique redox properties, oxygen storage capacity and acidity or alkalinity. SCR catalysts are easily deactivated in the presence of SO2 in real flue gas due to the competitive adsorption of SO2 and reactant molecules, as well as the oxidation and transformation of SO2 on catalyst surface, but the clear understanding on the SO2 poisoning mechanism of ceria-based SCR catalysts is severely limited until now. It has been found that the sulfur tolerance of SCR catalysts is related to the acidity of support, the texture of catalyst and the electron deficiency of center metal. In this project, CeO2/TS catalysts with different Ce4+/Ce3+ ratio, oxygen vacancy concentration, surface acidity or alkalinity and etc., will be synthesized controllably through adjusting the Ti/Si ratio of composite titanium-silicon oxide and using the organic ligand-assisted deposition technique. The adsorption/desorption and reaction of reactant molecules, such as SO2, NO and NH3, on the surface of CeO2/TS catalysts will be investigated, and the changes of catalysts and reactant molecules in the NH3-SCR reaction will be tracked with the aid of various in situ characterization techniques, to reveal the SO2 poisoning mechanism of CeO2/TS catalysts and the relationship between the catalyst structure and the SO2 poisoning mechanism in the NH3-SCR reaction.

NH3-SCR技术是去除NOx的有效途径，但传统钒钛基SCR催化剂存在钒物种毒性大、催化SO2氧化活性高及工作温度高等问题。氧化铈具有独特的氧化还原性、储氧能力及酸碱性，成为极具希望的绿色SCR催化剂。但实际烟气中的SO2在催化剂表面的竞争吸附及氧化转化会导致SCR催化剂严重失活。迄今人们对铈基SCR催化剂的SO2中毒机理尚缺乏清楚认识。研究发现SCR催化剂的抗硫性能与载体表面酸性和金属缺电子状态等结构因素相关。本项目拟通过调节钛硅复合氧化物(TS)的Ti/Si比例和采用有机配体辅助沉积技术调控CeO2/TS催化剂中Ce4+/Ce3+比例、氧空位浓度及表面酸碱性等结构因素，考察SO2、NO和NH3等反应物分子在CeO2/TS表面的吸/脱附行为和反应过程，追踪催化剂结构因素和反应物分子在NH3-SCR反应中的演变过程，揭示CeO2/TS催化剂的SO2中毒机理及其与结构因素之间的关联。

氧化铈具有独特的氧化还原性、储氧能力及酸碱性，成为极具希望的绿色SCR催化剂。但实际烟气中的SO2在催化剂表面的竞争吸附及氧化转化会导致SCR催化剂严重失活，而且人们对铈基SCR催化剂的SO2中毒机理还缺乏清晰认识。本项目旨在揭示铈基SCR催化剂的SO2中毒机理及其与催化剂结构因素之间的关联。受机械化学法在金属-有机骨架材料（MOFs）合成中的成功应用的启发，我们开发了一种“有机羧酸配体辅助球磨法”来合成高活性铈基SCR催化剂。发现有机配体可以有效地调节铈基复合氧化物的表面微结构、Ce4+/Ce3+比例、氧化还原性、分散度等性质。FT-IR、XRD、TPR、XPS、SEM及TEM等表征结果表明，铈基SCR催化剂良好的氧化还原性能及独特的多级孔结构是其具有较高NH3-SCR活性的主要原因。进一步研究还发现铈基SCR催化剂的表面微结构及氧化还原性等因素对SO2的吸附及硫物种在催化剂表面的氧化转化有显著影响。铈基SCR催化剂样品上亚硫酸盐转化为硫酸盐的速度越低，催化剂体系中残存的硫物种就相对越少，则抗硫性能好。这可能是影响铈基SCR催化剂抗硫性能的主要原因。