SAPO-11 molecular sieve synthesized via a novel alcohol–water solvent vapor-induced self-assembly conversion method and the hydroisomerization performance of its NiWS-supported catalyst

Abstract

In this work, a SAPO-11 molecular sieve was successfully synthesized via an alcohol–water solvent vapor-induced self-assembly conversion method for the first time. Compared with the conventional hydrothermal crystallization method, the alcohol–water solvent vapor-induced self-assembly conversion method used the induction of alcohol–water solvent steam to drive the solid nucleation and crystallization of the SAPO-11 molecular sieve xerogel precursor. SAPO-11 molecular sieves synthesized by the two methods were used as supports and loaded with NiWS active phase to prepare n-hexadecane hydroisomerization catalysts. The effects of the alcohol–water solvent vapor-induced self-assembly conversion method on the physicochemical properties of SAPO-11 were studied. Compared with the conventional hydrothermal crystallization method, the alcohol–water solvent vapor-induced crystallization method improved the pore structure and acidity of SAPO-11, promoted the dispersion of silicon species in SAPO-11, and inhibited Ostwald ripening during the formation of SAPO-11. The crystallization process of SAPO-11 synthesized via the alcohol–water solvent vapor-induced self-assembly conversion method was thoroughly investigated, and the mechanism of the crystallization was discussed. When SAPO-11 synthesized via alcohol–water solvent vapor-induced self-assembly conversion method was used as the support, the MSI of the catalyst weakened and the dispersion and stacking number of the sulfided active phase and the sulfidation degree of the active metals improved. The catalytic results of n-hexadecane hydroisomerization showed that SAPO-11 synthesized via the alcohol–water solvent vapor-induced self-assembly conversion method-based catalyst had higher catalytic activity and target product selectivity than the conventional SAPO-11-based catalyst. The catalytic kinetics of the catalysts were investigated in depth. The results showed that the metal site-acid site synergistic catalytic mechanism of SAPO-11 synthesized using the alcohol–water solvent vapor-induced self-assembly conversion method-based catalyst was better than that of the conventional SAPO-11-based catalyst. When SAPO-11 synthesized via the alcohol–water solvent vapor-induced self-assembly conversion method was used as the support, the hydroisomerization reaction path priority and hydroisomerization depth of the n-hexadecane hydroconversion over the catalyst improved and deactivation resistance was optimized. The approach is expected to provide a new route and reference for the synthesis of high-performance SAPO-11 molecular sieves and the design of high-efficiency hydroisomerization catalysts.