In situ synthesis of Nb-modified AFI topology molecular sieve and its modulation on the formantion of high-efficiency catalyst for 4,6-dimethyldibenzothiophene hydrodesulfurization

Abstract

Herein, molecular sieves with Nb and Si modified AFI-type structures were successfully synthesized in situ via a hydrothermal synthesis method. Subsequently, the corresponding NiW catalysts modified by the molecular sieve were obtained through incipient co-impregnation. The performance of NiW catalysts for 4,6-dimenthyldibenzothiophene (4,6-DMDBT) was comprehensively investigated. A series of characterizations demonstrated that Nb species were uniformly distributed within the AFI framework. This not only resulted in an increase in the acidic sites of both molecular sieves and hybrid-support (NbSAPO-5-alumina), but also effectively modulated the interaction between hybrid support and active metals. This led to a higher stacking numbers, which facilitated the sulfidation of W and Ni species, ultimately promoting the formation of more active edge sites on WS₂ slabs. This resulted in the catalyst NiW/NbSAPOA achieving a significantly higher desulfurization ratio of 95.8 % for 4,6-DMDBT at 280 ℃. Furthermore, the catalyst NiW/NbSAPOA exhibited the highest turnover frequency of 9.17 × 10⁻⁴ s⁻¹, and markedly enhanced selectivity for the direct desulfurization pathway in 4,6-DMDBT HDS.