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

• Applicants: Professor Dr. Jürgen Haase; Professor Dr. Jörg Kärger
• Subject Area: Physical Chemistry of Molecules, Liquids and Interfaces, Biophysical Chemistry ; Physical Chemistry of Solids and Surfaces, Material Characterisation
• Term: from 2014 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 259001939

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.

• DFG Programme: Research Grants