Alkylphosphonic acid- and small amine-templated synthesis of hierarchical silicoaluminophosphate molecular sieves with high isomerization selectivity to di-branched paraffins

The P atoms in alkylphosphonic acid are introduced into the SAPO-11 framework, and thus the long alkyl groups bonded with these P atoms induce the formation of intracrystal mesopores after calcination. The interpenetrating micro–mesoporous channels of the hierarchical SAPO-11 endow the resulting catalyst with the superior di-branched isomer selectivity. [Display omitted] ► The P atoms in alkylphosphonic acid are introduced into the SAPO-11 framework. ► The long alkyl groups bonded with these P atoms induce intracrystal mesopores. ► The hierarchical SAPO-11-based catalyst has superior di-branched isomer selectivity. This article proposes a one-step strategy to hydrothermally synthesize SAPO-11 with hierarchical micro- and meso-porous structure. The structure and acidity properties and the isomerization performance of the resulting hierarchical SAPO-11 were extensively characterized and assessed, respectively, and compared with those of a microporous SAPO-11. The results showed that the SAPO-11 with mutually interpenetrating micropores and mesopores had been obtained by introducing tetradecylphosphoric acid into the synthesis system of microporous SAPO-11. Compared with microporous SAPO-11, the hierarchical SAPO-11 had much higher external surface and mesoporous volume, and more active sites with suitable Brönsted acid strength. These advantages endowed the hierarchical SAPO-11-based catalyst with superior isomerization activity, enhanced selectivity to di-branched products, and decreased cracking selectivity. The strategy proposed opens a new route to synthesizing a variety of hierarchical mesoporous SAPO molecular sieves for size-selective catalytic conversions of relatively large hydrocarbon molecules.