Direct synthesis of hierarchical SAPO-11 molecular sieve with enhanced hydroisomerization performance

Abstract

Hydroisomerization of light straight-chain paraffins to their branched isomers especially di-branched ones is considered as a promising technology to produce clean gasoline blending component with high octane number. In this article, we report a superior hydroisomerization catalyst that is based on a SAPO-11 molecular sieve (SAPO-11-H) simultaneously with smaller crystal size, hierarchical pore structure and enhanced acidity. This novel SAPO-11-H was successfully synthesized via a two-stage hydrothermal crystallization route by simultaneously using a cationic surfactant cetyltrimethylammonium bromide (CTAB) as template and a nonionic copolymer poly(ethylene oxide)‑block‑poly(propylene oxide)‑block‑poly(ethylene oxide) (F127) as crystal growth inhibitor. During the crystallization, CTAB plays roles in enhancing the acidity and creating the mesoporous structure, and F127 serves as a crystal growth inhibitor to control the crystals size. Compared to two Pt catalysts supported on a conventional SAPO-11 and a commercial SAPO-11, the SAPO-11-H supported Pt/SAPO-11-H catalyst with the same Pt loading (0.5 wt%) exhibited superior selectivity to di-branched C8 isomers and dramatically lower cracking selectivity in n‑octane hydroisomerization. The outstanding performance of Pt/SAPO-11-H is mainly attributed to two factors: one is the highly exposed pore mouths and hierarchical pore structure of SAPO-11-H that benefit the formation of di-branched isomers and avoid the cracking of the resultant di-branched isomers, and the other is the enhanced acidity that boosts the hydroisomerization activity.