Microimaging of diffusion and reaction of guest molecules in MFI-type zeolite crystals

MFI型沸石晶体中客体分子扩散和反应的显微成像

• 批准号: 437340252
• 负责人: Professor Dr. Roger Gläser
• 金额: --
• 依托单位: Institut für Technische Chemie
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/437340252?language=en
• 关键词: Microimaging; diffusion; reaction; guest; molecules

The gain in value-added products by the application of nanoporous materials for mass conversion and separation can never be faster than allowed by the transportation rate from the material interior to the surroundings. The rate of mass transfer within such materials is therefore, besides its relevance for fundamental research, among the key numbers deciding about their technological performance. Over decades, this type of information could only be deduced from “macroscopic” measurements, based on measurement of uptake and release rates with beds of crystals or pellets. Any message about the elementary processes of mass transfer had therefore to be based on model assumptions, which often were found to be wrong. Direct evidence about these inconsistencies was attained by advent of microscopic techniques of diffusion measurement, namely pulsed field gradient (PFG) NMR and microimaging by IR and interference microscopy, which often revealed discrepancies of orders of magnitude and did thus initiate a paradigm shift in our understanding of mass transfer in such materials. While microscopic diffusion techniques have so far been mainly applied to quite diverse nanoporous host-guest systems, selected with the main focus on demonstrating the potentials of these novel techniques quite in general, the present project aims on providing the proof of efficiency of these techniques by demonstrating the power of their evidence with a concerted application to MFI-type zeolite. It is a key material in zeolite catalysis and – given its highly complex pore structure – a challenging system for the in-depth study of mass transfer. The project will largely benefit from the complementarity of the two techniques. These are the options of NMR for revealing and analyzing reactants, intermediates and products during chemical reactions and for recording (via PFG NMR) the probability distribution of their displacement (including the short- and long-range diffusivities of all involved components) and the ability of microimaging to record transient concentration profiles which includes the measurement of intracrystalline fluxes. Though operating microscopically, with observing typically 1010 molecules both techniques provide data of high statistical relevance. The novel type of information aspired in the field of mass transfer includes the measurement of intracrystalline guest fluxes and the investigation of their mutual interference under multi-component adsorption, the in-depth study of transport enhancement by mesopores and the impact of transport resistances on the external surface as well as in composite materials (mixed matrix membranes). On considering conversion phenomena, guest-induced host variation (following indications of this phenomenon in first microimaging studies) just as host-induced guest variation shall be in the focus of our studies, in both cases in search for unprecedented information about the spatio-temporal variation over the individual MFI crystal.

通过应用纳米多孔材料进行质量转化和分离，增值产品的收益永远不会快于从材料内部到环境的运输速率所允许的速度。因此，除了与基础研究有关外，此类材料内的传质速率也是决定其技术性能的关键参数之一。几十年来，这种类型的信息只能从“宏观”测量中推断出来，这种测量是基于对晶体或颗粒床的吸收和释放速率的测量。因此，任何关于传质基本过程的信息都必须以模型假设为基础，而模型假设往往被发现是错误的。这些不一致性的直接证据是通过微观扩散测量技术的出现，即脉冲场梯度(PFG)核磁共振和红外和干涉显微镜显微成像的出现，这些技术往往揭示了数量级的差异，从而确实引发了我们对此类材料中传质的理解的范式转变。虽然到目前为止，微观扩散技术主要应用于相当多样化的纳米孔道主客体系统，主要集中在展示这些新技术的潜力，但本项目的目的是通过在MFI型沸石上的协同应用来证明这些技术的有效性。它是沸石催化的关键材料，由于其高度复杂的孔结构，对深入研究传质过程是一个具有挑战性的系统。该项目将在很大程度上受益于两项技术的互补性。这些是核磁共振的选择，用于揭示和分析化学反应中的反应物、中间体和产物，并记录(通过PFG核磁共振)它们置换的概率分布(包括所有相关组分的短期和远程扩散系数)，以及显微成像记录瞬时浓度分布的能力，包括测量晶体内的熔剂。虽然这两种技术都是在显微镜下操作，但通常观察1010个分子，这两种技术都提供了具有很高统计相关性的数据。传质领域需要的新型信息包括测量晶体内客体通量及其在多组分吸附下相互干扰的研究、深入研究介孔促进传递以及传递阻力对外表面以及复合材料(混合基质膜)的影响。考虑到转换现象，客体诱导的宿主变化(遵循在第一次显微成像研究中的这种现象的迹象)就像宿主诱导的客体变化一样将是我们研究的重点，在这两种情况下，都是为了寻找关于单个MFI晶体上的时空变化的前所未有的信息。