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.
Bibliographical noteFunding Information:
This work was supported by the Catalysis Center for Energy Innovation, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award DE‐SC0001004; and, in its earlier stages, by ADMIRE (Abu Dhabi‐Minnesota Institute for Research Excellence) through the Petroleum Institute (now Khalifa University of Science and Technology). Parts of this work were carried out in the Characterization Facility, University of Minnesota, which receives partial support from NSF through the MRSEC program. Y.G. acknowledges support from ADNOC (Abu Dhabi National Oil Company). We thank Dr. S. Hwang (Caltech) for performing the solid‐state NMR experiments.
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- electron tomography
- heterogeneous catalysis
- steam treatment
- two dimensional materials