Journal
CHEMISTRY-A EUROPEAN JOURNAL
Volume 23, Issue 41, Pages 9952-9961Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.201701978
Keywords
adsorption; alkylpyridines; Beckmann rearrangement; Bronsted acid sites; hierarchical SAPO-34; physicochemical characterization
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Funding
- Compagnia di San Paolo (HE-PYCHEM project)
- European Union's Horizon research and innovation programme [720783]
- Engineering and Physical Sciences Research Council (EPSRC, UK) [EP/K014706/1]
- Honeywell LLC
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Using a distinctive bottom-up approach, a hierarchical silicoaluminophosphate, SAPO-34, has been synthesized using cetyl trimethylammonium bromide (CTAB) encapsulated within ordered mesoporous silica (MCM-41) that serves as both the silicon source and mesoporogen. The structural and textural properties of the hierarchical SAPO-34 were contrasted against its microporous analogue, and the nature, strength, and accessibility of the Bronsted acid sites were studied using a range of physicochemical characterization tools; notably probe-based FTIR and solid-state magic angle spinning (SS MAS) NMR spectroscopies. Whilst CO was used to study the acid properties of hierarchical SAPO-34, bulkier molecular probes (including pyridine, 2,4,6-trimethyl-pyridine and 2,6-di-tert-butylpyridine) allowed particular insight into the enhanced accessibility of the acid sites. The activity of the hierarchical SAPO-34 catalyst was evaluated in the industrially-relevant, acid-catalyzed Beckmann rearrangement of cyclohexanone oxime to e-caprolactam, under vapor-phase conditions. These catalytic investigations revealed a significant enhancement in the yield of e-caprolactam using our hierarchical SAPO-34 catalyst compared to SAPO-34, MCM-41, or a mechanical mixture of these two phases. The results highlight the merits of our design strategy for facilitating enhanced mass transfer, whilst retaining favorable acid site characteristics.
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