基于实验与量化计算沸石分子筛含氰废气选择性催化燃烧微观机制研究

The nitrile gas emissions (HCN, CH3CN, and CH2CHCN) from the acrylonitrile industry are not well solved in our China now, which have caused great damage to the ecological environment. Present work aims to use the selective catalytic combustion (SCC) method to realize the economic, efficient, and high N2 selectivity removal of the nitrile gases. Zeolite catalyst having high specific surface area as well as good thermal stability was reported to be one kind of promising nitrile gas SCC catalyst. However, up to now, only a few works were reported using zeolite as the SCC catalyst for the nitrile gas catalytic abatement, resulting in that there are still many scientific questions needed be clarified. In light of this fact, present study will broaden the research scope and investigate the micro- and mesoporous zeolite catalyst with different configurations for the SCC of nitrile gases. Different kinds of transition metals ions (TMI) will be utilized to modify the zeolite catalyst for the purpose of selecting the excellent performance zeolite catalyst, and also a variety of experimental characterizations will be further conducted to analyze the relationship between the zeolite structure and its catalytic behavior. Moreover, the SCC mechanism over zeolite catalyst will be comprehensively investigated by employing both experimental and theoretical (density functional theory, DFT) approaches, aiming to clarify the detailed reaction path ways and conduct microkinetic analysis. Meanwhile, in light of the DFT simulations, the micro-mechanism between the zeolite topology and its catalytic behavior will also be further discussed. Finally, the electric field effect (EFE) of the zeolite catalyst will be studied by the charge transfer analysis of DFT and experimental study of DRIFTS, which can give a deeper insight into the relationship between the EFE of zeolite catalyst and its catalytic behavior, providing theoretical guidance for the design of high efficient zeolite catalyst.

针对我国丙烯腈工业含氰废气（氰化氢、乙腈、丙烯腈）尚未得到有效治理，对生态环境造成极大危害，本课题拟采用选择性催化燃烧法，实现其经济、高效、高N2选择性催化脱除。分子筛具有较高的比表面积、良好的热稳定性，近年来，被发现是一种理想的含氰废气选择性催化燃烧催化剂，然而，目前国内外相关研究报道较少，许多科学问题尚未明晰。本项目拟拓宽研究范围，以不同构型微、介孔分子筛为研究对象，匹配不同过渡金属离子改性，筛选性能优异分子筛催化剂，并通过多种实验表征技术手段，分析其构效关系；其次，将采用实验与量化计算相结合的研究方法，深入探究反应机理，明晰具体反应路径，并进行微观动力学分析；与此同时，通过量化计算建模，深入阐明分子筛空间构型与其催化性能间的内在关系；最后，基于量化计算电子转移分析及原位红外，揭示分子筛电场效应与其催化燃烧性能间的微观作用机制，为高性能沸石分子筛催化剂设计提供理论指导。

近年，我国大气污染日益严重，高效大气污染治理技术亟待开发，鉴于此，本课题基于多种不同构型微、介孔沸石分子筛催化剂为研究对象，采用实验及量化计算相结合的研究方法，对含氰废气（氰化氢，丙烯腈）选择性催化燃烧技术展开系统研究，着重对催化剂催化性能、构效关系、反应机理、微观动力学、电子转移等微观作用机制展开探究。研究结果表明，经Cu离子改性Cu-ZSM-5、Cu-Beta分子筛具有最优的催化活性及N 2选择性，其可在350 oC实现含氰废气的100%分解，且N2选择性大于80%。H2程序升温还原（H2-TPR）、X射线衍射（XRD）、X射线光电子能谱分析（XPS）等多种表征分析结果进一步表明交换于分子筛Brönsted酸位的Cu+离子为反应活性中心，且其Cu2+ → Cu+氧化还原性决定反应活性及N2选择性，较其他构型分子筛，Cu-ZSM-5、Cu-Beta具有最优的Cu2+ → Cu+氧化还原性，因此其催化性能最优。此外，本课题采用原位红外（in-situ DRIFTS）及密度泛函理论（DFT）模拟含氰废气催化燃烧反应机理、计算反应能垒、并展开微观动力学、电子转移分析。研究发现含氢废气催化燃烧存在两种反应机理，氧化机理及水解机理：在无H2O参与反应条件下，反应主要产生NCO中间物种，其可氧化生成NO，NO与NCO进一步反应，生成最终产物N2，该反应路径能垒最低，为最优反应路径；在有H2O参与反应条件下，反应将发生水解反应，产生中间物种NH3，NH3经选择性氧化，生成最终产物N2。基于量化计算，进一步探究不同活性中心结构（单[Cu]+, 双[Cu]+, [Cu-O-Cu]2+）对反应性能的影响，研究结果表明双[Cu]+活性中心存在空间协同效应，其可有效降低含氰废气催化分解能垒，然而，[Cu-O-Cu]2+活性中心结构与单[Cu]+活性中心催化反应能垒相近。最后，本项目采用Mulliken电子转移分析，对上述不同活性中心结构反应关键步骤展开研究，结果表明，双[Cu]+在反应过程中同样存在电场协同作用，该双活性中心一个表现为电子受体，一个表现为电子供体，协同作用于吸附与孔道内部的反应物分析，进而更易使得H-CN键发生极化、断裂，因此，Mulliken 电子转移分析从更加深入揭示双[Cu]+活性中心优异的催化性能。