Synthesis of nano-sized small-crystal and hierarchical SAPO-11 molecular sieves and superior catalytic performance of their NiWS-supported catalysts in hydroisomerization of n-hexadecane

The nano-sized small-crystal and hierarchical SAPO-11 molecular sieves were successfully synthesized with l-Lysine as the crystal growth inhibitor, and their particle size reached 80 nm at the minimum, and the crystal size was 22.1 nm. With the synthesized SAPO-11 molecular sieve as support, the corresponding NiW supported catalyst was prepared for the hydroisomerization of n-hexadecane. The properties of small-crystal and hierarchical SAPO-11 molecular sieve and catalyst were analyzed by a series of physicochemical characterizations, and the formation mechanism of small-crystal and hierarchical SAPO-11 molecular sieve was proposed. The results showed that the reduction of crystal size greatly improved the BET specific surface area, mesopore volume of SAPO-11 molecular sieve. The decrease of crystal size increased the surface Si content of SAPO-11 molecular sieve, thus improving the surface acidity of SAPO-11 molecular sieve, and weakening the interaction between active metals and supports of the catalysts. In addition, the decrease of crystal size increased the dispersion and stacking number of the active phases, thus greatly improving the catalytic performance of the catalysts. Compared with the catalyst corresponding to the conventional SAPO-11 molecular sieve, the yield of i-hexadecane of the catalyst corresponding to small-crystal and hierarchical SAPO-11 molecular sieve increased by 45.34%.