Synthesis of hierarchically radiated SAPO-11/Silica composites to boost n-alkane hydroisomerization

Abstract

Hierarchically radiated SAPO-11 molecular sieves (RS-11-x, x was the initial SiO2/Al2O3 molar ratio) were prepared by employing different amounts of un-calcined radiated mesoporous SiO2 nanoparticles (RMSNs) as silicon source and template, and the corresponding Pt-based catalysts were applied for n-decane hydroisomerization. During the synthesis of RS-11-x, RMSNs were hydrolyzed into active Si species slowly due to the supporting of CTAB in their channels, and these active Si species interacted with Al and P species on the RMSNs to generate SAPO-11 crystal nuclei. Ultimately, hierarchical SAPO-11 molecular sieves with radiated morphologies were dispersed on the RMSNs. Among RS-11-x, RS-11-0.4 possessed the greatest medium and strong Brønsted acid sites (MSBAS) content (14.9 μmol/g) as well as superior external surface area (247 m2 g−1) and mesopore volume (0.433 cm3 g−1). Furthermore, compared with the SAPO-11 synthesized by tetraethyl orthosilicate (TEOS) and the mixture of CTAB and TEOS as silicon precursors, respectively, RS-11-0.4 possessed a larger external surface area, a higher mesopore volume and the optimal MSBAS content. Consequently, the Pt/RS-11-0.4 catalyst showed a higher selectivity of branched C10 isomers (93.5%), a better selectivity of multi-branched C10 isomers (33.8%), and a lower cracking selectivity (6.3%) than the counterpart catalysts. This work offers a new strategy for preparing hierarchical molecular sieves with superior catalytic performances.