Small-crystal and hierarchical SAPO-11 molecular sieve synthesized via three-stage crystallization method and hydroisomerization performance of corresponding NiWS supported catalyst

In order to prepare non-noble metal supported hydroisomerization catalyst with high catalytic performance, this work first proposed a novel three-stage crystallization method to synthesize small-crystal and hierarchical SAPO-11 molecular sieve, and prepared the corresponding NiWS supported catalyst for the hydroisomerization of n-hexadecane. The physicochemical properties of the small-crystal and hierarchical SAPO-11 molecular sieve and the NiWS supported catalyst were analyzed via a series of characterization methods. It was found that the crystal size of SAPO-11-S was reduced to 21.8 nm and the particle size was reduced to 70–140 nm. SAPO-11-S was superior to SAPO-11-C in pore properties and acidity. The reason for the increase of the number of medium-strong B acid sites in SAPO-11-S was investigated by 29Si MAS NMR characterization, and the formation mechanism of SAPO-11-S was proposed by tracking and analyzing the crystallization process of SAPO-11-S. The decrease of crystal size of SAPO-11 molecular sieve effectively improved the sulfidation degree of active metals and the dispersion degree of the active phase of the catalyst, and promoted more active phases to form “type II active phase”. Compared with NiW/SAPO-11-C, NiW/SAPO-11-S showed higher catalytic activity and isomerization selectivity, and the maximum i-hexadecane yield of NiW/SAPO-11-S was 44.77% higher than that of NiW/SAPO-11-C.