3 years ago

Mesoporous Silica Scaffolds as Precursor to Drive the Formation of Hierarchical SAPO-34 with Tunable Acid Properties

Mesoporous Silica Scaffolds as Precursor to Drive the Formation of Hierarchical SAPO-34 with Tunable Acid Properties
Enrica Gianotti, Robert Raja, Stephanie Chapman, Giorgio Gatti, Ivana Miletto, Leonardo Marchese, Geo Paul
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 Brønsted 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-trimethylpyridine 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 ϵ-caprolactam, under vapor-phase conditions. These catalytic investigations revealed a significant enhancement in the yield of ϵ-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. Precursor driven formation: Hierarchical SAPO-34 has been synthesized with a distinctive bottom-up approach, using CTAB encapsulated within ordered mesoporous silica that serves as both the silicon source and mesoporogen.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/chem.201701978

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