Mesoporogen-free synthesis of hierarchical SAPO-11 from kaolin for hydroisomerization of n-alkanes

Abstract

Hierarchical SAPO-11, featuring both micropore and mesopore channels, demonstrates an outstanding performance in high-octane gasoline production. In this work, we propose an economic and effective approach to directly fabricate hierarchical SAPO-11 molecular sieve from natural kaolin, eliminating the need for mesoporogens. The systematic characterization results show that the kaolin-derived SAPO-11 possesses abundant micro-mesoporous structure and more Brønsted (B) acid sites on the external surface in contrast with the conventional SAPO-11 prepared employing silica sol as silicon source as well as SAPO-11 synthesized with the assist with of poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (F127). The analysis of the formation process reveals that the kaolin not only provides silicon source for the SAPO-11 crystal growth, but also offers confined environment for crystal growth along the preferential orientation, resulting in the generation of the microporous and mesoporous structure. Benefiting from these unique properties, the kaolin-derived Pt/SAPO-11 exhibits considerably improved selectivity for di-branched C₈ isomers in n-octane hydroisomerization.