Micro-Imaging of Transient Concentration Profiles of Guest Mixtures in Zeolite Crystals

晶内扩散系数是决定纳米多孔材料技术应用有效性的关键参数之一，特别是在通过选择性吸附进行质量分离和通过多相催化进行质量转化方面。在混合物中的扩散是特别相关的，因为在所有这些应用中，传质发生在多组分吸附的条件下。对于平衡测量，我们处置，与脉冲场梯度（PFG）NMR方法，一个强大的，完善的技术。然而，在非平衡条件下的晶内扩散的测量，已经成为可能，只有在过去的十年中引入显微成像技术，特别是干涉显微镜和红外显微光谱，从而提供了记录瞬态晶内浓度分布的选择。目前，显微成像技术主要应用于单组分吸附的研究。混合物吸附的现象，一般认为，只有在一个整体模式，即作为平均的浓度的各个组成部分所考虑的晶体。在本项目中，我们将克服这一限制，将我们的注意力集中在选择性测量不同混合物组分的分布和由此记录的剖面的时间演变上。到目前为止，这类信息无法通过直接观察获得。克服这一限制为我们提供了可能性，以实验确定的扩散矩阵的各种元素，在多组分吸附的条件下，假设的扩散系数的位置作为一个标量。

The intracrystalline diffusivity is among the key parameters deciding about the effectiveness of the technological application of nanoporous materials, notably in mass separation by selective adsorption and mass conversion by heterogeneous catalysis. Diffusion in mixtures is of particular relevance since, in all these applications, mass transfer occurs under the conditions of multicomponent adsorption. For equilibrium measurements we dispose, with the pulsed field gradient (PFG) NMR method, of a powerful, well-established technique. The measurement of intracrystalline diffusion under non-equilibrium conditions, however, has become possible in only the last decade with the introduction of the techniques of micro-imaging, notably of interference microscopy and IR micro-spectroscopy, and the thus provided option of recording transient intracrystalline concentration profiles. So far, the methods of micro-imaging were mainly applied for the investigation of single-component adsorption. Phenomena of mixture adsorption were, generally, considered in only an integral mode, namely as the average of the concentrations of the individual components taken over the considered crystal. With the present project we are going to overcome this limitation by directing our attention on the selective measurement of the distribution of the different mixture components and the temporal evolution of the thus recorded profiles. So far, this type of information was inaccessible by direct observation. Overcoming this limitation provides us with the possibility to experimentally determine the various elements of the diffusion matrix which, under the conditions of multicomponent adsorption, assume the position of the diffusion coefficient as a scalar quantity.