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Creating Accessible Active Sites in Hierarchical MFI Zeolites for Low‐Temperature Acid Catalysis
Author(s) -
Erigoni Andrea,
Newland Stephanie H.,
Paul Geo,
Marchese Leonardo,
Raja Robert,
Gianotti Enrica
Publication year - 2016
Publication title -
chemcatchem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.497
H-Index - 106
eISSN - 1867-3899
pISSN - 1867-3880
DOI - 10.1002/cctc.201600729
Subject(s) - microporous material , beckmann rearrangement , catalysis , zeolite , chemistry , fourier transform infrared spectroscopy , chemical engineering , heterogeneous catalysis , inorganic chemistry , materials science , organic chemistry , engineering
A versatile desilication design strategy for the creation of hierarchical H–ZSM‐5 zeolite catalysts with different Si/Al ratios has been demonstrated. The nature, strength, and the accessibility of the acid sites after the alkaline treatment was elucidated by employing a range of physico‐chemical characterization tools; notably probe‐based FTIR spectroscopy along with Solid State (SS) MAS NMR spectroscopy. In addition, structural and textural properties of the hierarchical zeolites were also explored and compared to their corresponding microporous analogues. CO was used to probe the acidic properties of the hierarchical zeolites with the concomitant deployment of a bulky molecular probe, 2,4,6‐trimethylpyridine (collidine), which is too large to access the micropores, to specifically investigate the enhanced accessibility of the active sites. The hierarchical zeolites were evaluated in the industrially relevant, acid‐catalyzed Beckmann rearrangement of cyclohexanoneoxime to ϵ ‐caprolactam, the precursor for Nylon‐6, in liquid phase and at low temperatures. The catalytic findings with the hierarchical catalysts reveal a significant enhancement in the production of ϵ ‐caprolactam, compared with the parent microporous H–ZSM‐5 zeolite, thereby highlighting the merits of our design approach in facilitating enhanced diffusion and mass transfer.