高抗硫抗水性低温脱硝催化剂的结构设计和反应机制研究

To develop low temperature SCR catalysts with high resistance to sulfur dioxide and water has drawn great attention at home and abroad, and is also crucial for the development and application of low temperature SCR technologies. The objective of this project is to study the regularity of adjustments for the porous structure and chemical environment of manganese loaded silicoaluminophosphate molecular sieves(Mn-SAPO-n), and the reaction mechanism of low temperature SCR reaction while the sieves as the catalysts. Tansition metal Mn is introduced into SAPO-n with different pore diameters,and then the synthesis mechanism of high active component will be studied.The pore structure of Mn-SAPO-n will be regulated precisely by a chemical liquid deposition method(CLD), and then the screening effect of SO2 and the performance of the catalysts will be studied. Then,the structures of low temperature SCR catalysts with high activity as well as high resistance to sulfur dioxide and water are designed by applying the combinatorial chemistry method, based on the structural characteristics, chemical environment, and the selective adsorption of Mn-SAPO-n.The internal relationships between the structural characteristics, adsorption and desorption characteristics and the catalytic performance will reveal the reaction mechanism of low temperature SCR reaction on Mn-SAPO-n catalysts, which provides theoretical basis for the design, optimization of low temperature SCR catalysts with high activity and high resistance to sulfur dioxide and water.

高抗硫抗水性能的催化剂体系是低温SCR脱硝技术发展和应用的关键，也是目前国内外研究的热点。本项目研究负载过渡金属锰的磷酸硅铝系列分子筛（Mn-SAPO-n）低温烟气脱硝催化剂的微观化学环境和孔道结构调控规律、抗硫抗水性能及其催化作用机理。以不同孔径的SAPO-n为载体，引入过渡金属元素Mn为低温SCR反应活性组分，研究合成高活性低温SCR催化剂的调控规律；通过化学液相沉积法对Mn-SAPO-n的孔径进行精细调控，研究Mn-SAPO-n孔道结构对SO2筛分效果以及催化剂性能的影响；利用Mn-SAPO-n的结构特性和化学环境以及气体选择性吸附特性，并运用组合化学的方法，构筑新型的具有高活性高抗硫抗水性能的低温SCR脱硝催化剂体系；研究催化剂结构、吸附脱附特性与催化性能之间的内在规律，揭示Mn-SAPO-n的低温SCR催化反应机制，为高活性高抗毒的低温SCR催化剂的设计和优化提供重要的理论依据。

本研究首先以水热法制备了不同形貌的纳米MnOx催化剂并考察了其低温SCR脱硝性能，并对MnOy纳米片进行了Ce的掺杂改性。考察了内核形貌和核壳配比等因数对CeO2@MnOx核壳结构催化剂低温SCR性能以及抗硫抗水性能的影响，并探讨了其反应机理。其次，以不同孔径的SAPO-n分子筛为载体，研究了载体结构及表面酸性对负载型催化剂的低温SCR性能的影响。制备了高分散的MnOx/SAPO-34催化剂并对其进行了Pr/Ce掺杂改性以及SCR反应机理的研究，并将活性组分引入SAPO-34骨架中原位合成了富锰MnSAPO-34和MnCu-SAPO-34催化剂并研究了其低温SCR性能。最后，将Ce原位引入/负载于Mn/SAPO-34制备了Mn-Ce/CeAPSO-34催化剂，研究了Ce在载体骨架和表面两种存赋状态对催化剂低温SCR性能的影响，并应用原位红外光谱分析和密度泛函理论计算方法深入探讨了其抗硫抗水反应机理。研究结果表明，MnO2纳米片表现出优异的低温SCR活性，Ce的掺杂降低了MnO2的结晶度，提高了高价态锰和化学吸附氧物种的比例，增加了催化剂表面强酸性位点。纳米CeO2@MnOx催化剂具备优异的低温SCR性能，归因于其高比例的Mn4+和Ce3+和高活性的MnO2（110）晶面，其低温SCR反应同时遵循L-H和E-R机理。 SAPO-n分子筛负载型催化剂中，MnOx/SAPO-34催化剂表现出最佳的低温SCR活性，高价态锰的比例和适宜的Lewis酸性位点的量对低温SCR反应起关键作用。高分散MnOx/SAPO-34催化剂中活性组分MnOx高度分散在载体表面，呈现了优异的低温SCR性能，反应过程同时存在L-H和E-R两种机制，并以E-R机理为主。Pr/Ce掺杂提高了MnOx/SAPO-34催化剂的低温活性和抗硫水性能，Pr或Ce能优先与SO2结合而抑制Mn的硫酸化；Cu的掺杂显著地提高了原位合成的MnCu-SAPO-34分子筛的低温SCR性能，孤立的铜离子物种与骨架中的Mn(IV)物种之间存在协同作用。Mn-Ce/CeAPSO-34催化剂中，Ce原位引入和负载于Mn/SAPO-34两者之间具有协同效应，骨架上的Ce和负载于表面的Ce形成的[-Ce-O-Ce-]基团有利于SO2和H2O优先在该位点上吸附，从而避免了Mn的硫酸化，提高了催化剂的低温SCR活性和抗硫抗水性能。