基于V-ZSM-5分子筛催化剂乙烷氧化脱氢体系的设计构建与紫外共振拉曼光谱研究

Oxidative dehydrogenation of ethane (ODE) to ethylene with low energy consumption and great application potential has been attracting much attention. Although numerous catalysts, represented by vanadium oxide based catalytic materials, have been reported in literatures, the performance for ODE was still relatively low, and there were still not very clear about catalytic active site, the role of catalyst acidity in ODE and reaction mechanism. To solve these problems, this project will innovatively develop V-ZSM-5 zeolite based catalyst with both oxidation site and acid site, and adopt powerful UV resonance Raman spectroscopy to study ODE system for the first time. With the effects of some hydrothermal conditions (initial Si/V, Si/Al ratios and alkalinity) on the incorporation of vanadium and aluminum into zeolitic framework studied by UV resonance Raman spectroscopy and 27Al solid state NMR spectroscopy, synthesis of V-ZSM-5 zeolites with various framework Si/V and Si/Al ratios can be easily fulfilled. Then the promotion effects of Brønsted acidity and modification with transitional metal oxide on ODE process will be investigated to achieve the development of high-performance V-ZSM-5 zeolite based catalyst. On the basis, ODE process will be studied by in situ UV resonance Raman spectroscopy to deepen the understanding of catalytic active site, the role of catalyst acidity in ODE and reaction mechanism, which would be helpful for developing highly excellent ODE catalyst.

低能耗、应用潜力巨大的乙烷氧化脱氢制乙烯路线正受到人们的广泛关注。虽然以氧化钒基催化材料为代表的不少催化剂被报道出来，但乙烷氧化脱氢的性能仍然偏低，对催化活性中心、催化剂酸性在反应中所起作用和反应机理的认识仍然不够深入。为了解决这些问题，本项目创新地发展兼具氧化位和酸性位的V-ZSM-5分子筛基催化剂，并首次采用先进的紫外共振拉曼光谱研究乙烷氧化脱氢体系。重点研究初始溶/凝胶中的Si/V和Si/Al比及碱度对钒与铝进入分子筛骨架的影响规律，进而实现各种骨架Si/V和Si/Al比的V-ZSM-5分子筛的合成。然后重点考察Brønsted酸性和过渡金属氧化物修饰对乙烷氧化脱氢反应的促进作用，以开发出较高性能的V-ZSM-5分子筛基催化剂。在此基础上，采用原位紫外共振拉曼光谱研究乙烷氧化脱氢过程，深入认识催化活性中心、催化剂酸性在反应中所起作用和反应机理，为开发性能优异的催化剂提供理论指导。

根据项目计划书，开展了V-ZSM-5分子筛的合成、表征及催化乙烷氧化脱氢性能评价工作。由于在碱性条件下合成及V与Al之间存在相互作用，所得的V-ZSM-5分子筛V含量低、骨架Si/V和Si/Al比无法有效地调控，进而在催化乙烷氧化脱氢上表现出较低的催化性能。鉴于此，也对Ti-MWW分子筛研究中酸处理的确切作用、怎样的TiO4物种活性最高以及如何简单、有效地暴露十二元环半超笼等关键科学问题开展了研究工作，取得了一些原创成果。发现酸处理无硼Ti-MWW分子筛原粉不仅除去了部分低活性的非骨架TiOm (m=5, 6)物种，还使另一部分转变为高活性的骨架TiO4物种，这一观点之前从未被报道过。TiO4物种活性由高到低顺序为：骨架Ti(OSi)4物种 > 骨架Ti(OSi)3OH物种 >> 处于无定型SiO2中的TiO4物种。酸处理含硼Ti-MWW分子筛原粉可使部分非活性的非骨架TiO6物种转变为活性的骨架TiO4物种，酸处理直接焙烧样则使几乎全部非活性的非骨架TiO6物种转变为非活性的锐钛矿TiO2。开发了有机硅原位层剥离制备薄层Ti-MWW分子筛的方法，制得的Ti-MWW分子筛的厚度为10~20 nm，其在环己烯环氧化中展现出比常规Ti-MWW分子筛更优异的催化性能。这些认识或结果对Ti-MWW分子筛的进一步研究和高效钛硅分子筛催化剂的开发都有较大的帮助。

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