| Institution: | 1. Department of Chemical Engineering and Materials Science, University of Minnesota, 421 Washington Avenue SE, Minneapolis, MN, 55455 USA;2. Peter A. Rock Thermochemistry Laboratory, NEAT-ORU, University of California Davis, Davis, CA, 95616 USA;3. Department of Chemical Engineering, Khalifa University of Science and Technology, Habshan Building, Sas Al Nakhl Campus, Abu Dhabi, United Arab Emirates;4. Department of Diagnostic and Biological Sciences, University of Minnesota, 515 Delaware St SE, Minneapolis, MN, 55455 USA
Characterization Facility, University of Minnesota, 312 Church St, Minneapolis, MN, 55455 USA |
| Abstract: | Commonly used methods to assess crystallinity, micro-/mesoporosity, Brønsted acid site density and distribution (in micro- vs. mesopores), and catalytic activity suggest nearly invariant structure and function for aluminosilicate zeolite MFI two-dimensional nanosheets before and after superheated steam treatment. Yet, pronounced reaction rate decrease for benzyl alcohol alkylation with mesitylene, a reaction that cannot take place in the zeolite micropores, is observed. Transmission electron microscopy images reveal pronounced changes in nanosheet thickness, aspect ratio and roughness indicating that nanosheet coarsening and the associated changes in the external (mesoporous) surface structure are responsible for the changes in the external surface catalytic activity. Superheated steam treatment of hierarchical zeolites can be used to alter nanosheet morphology and regulate external surface catalytic activity while preserving micro- and mesoporosity, and micropore reaction rates. |
