|When:||Thursday, February 14, 2013|
4:00 PM - 5:00 PM
Ryan Hall, 4003 |
2190 Campus Drive
Evanston, IL 60208 map it
|Audience:||- Faculty/Staff - Student - Public|
|Contact:||James M Puricelli
|Group:||Center for Catalysis and Surface Science|
In-situ Spectroscopy of Catalytic Solids at the Single Particle Level
Bert M. Weckhuysen*
Debye Institute for Nanomaterials Science, Utrecht University,
Universiteitsweg 99, 3584 CG Utrecht, The Netherlands
Heterogeneous catalysis is a fascinating, but complex multidisciplinary science, which is core business to our energy, automotive, chemical and pharmaceutical industries as most chemical reactions are catalyzed by at least one material containing a multitude of often distinct catalytic functionalities. Although progress has been made in our understanding of catalytic solids, their functioning under realistic reaction conditions represents still a very important scientific challenge to both academia and industrial scientists. Deep mechanistic insight in the fundamentals of heterogeneous catalysis can only be acquired by using advanced characterization methods as well as proper in-situ reaction cells and related measurement protocols. In recent years we have seen the development of space-resolved and tomographic characterization approaches, ultimately allowing performing single molecule-single catalyst particle in-situ studies.
In this lecture, such advanced spatiotemporal characterization methods for the characterization of individual zeolite crystals will be discussed. First, the intergrowth structure of zeolite H-ZSM-5 crystals is elucidated in great detail. For this purpose, a template burning method has been developed with confocal fluorescence microscopy, whereas the pore orientation of the individual building blocks can be assessed with Electron Back-Scattering Diffraction and Focused Ion Beam milling (EBSD-FIB). By analyzing a large set of various morphological distinct large H-ZSM-5 crystals a unifying view on the intergrowth structure of these materials could be obtained. Furthermore, by using TEM lamelling, electron diffraction studies in combination with AFM and XPS, it was possible to reveal outer and inner surface molecular diffusion boundaries affecting the overall performance of the crystals. In a second step, UV-Vis, synchrotron IR and fluorescence microscopy has been employed to map the formation of reaction products and the absorption spectra obtained allow for a kinetic analysis of the reaction products formed. In a third step, 3-D maps of the reactant and product molecules within the crystal are visualized with Coherent Anti-Stokes Raman Scattering (CARS) and confocal fluorescence microscopy. We have shown the capabilities of this multi-technique approach by using the styrene oligomerization as probe reaction for mapping Brønsted acidity in H-ZSM-5 crystals. Furthermore, we have extended this methodology to study the effect of mesoporosity in H-ZSM-5 crystals on their acidity, Al distribution and catalytic reactivity. In a final part of the lecture, in-situ nanoscale chemical imaging of zeolites will be presented by making use of the recently developed Scanning Transmission X-ray Microscopy (STXM) method.