Mesoporous Silica Scaffolds as Precursor to Drive the Formation of Hierarchical SAPO‐34 with Tunable Acid Properties. Issue 41 (28th June 2017)

• Record Type: Journal Article
• Authors: Miletto, Ivana; Paul, Geo; Chapman, Stephanie; Gatti, Giorgio; Marchese, Leonardo; Raja, Robert; Gianotti, Enrica
• Is Part Of: Chemistry. Volume 23:Issue 41(2017)
• Page Start: 9952
• Page End: 9961
• Publication Date: 2017-06-28
• Subjects: adsorption -- alkylpyridines -- Beckmann rearrangement -- Brønsted acid sites -- hierarchical SAPO-34 -- physicochemical characterization; Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.201701978
• Languages: English
• ISSNs: 0947-6539

Abstract

Abstract: 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. Abstract : 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.