Dendritic micro-mesoporous composites via nano-assembly strategy towards high-efficiency catalysts for hydrodesulfurization of dibenzothiophenes

Based on the three-dimensional center-radial framework structure of dendritic mesoporous silica nanospheres (DMSNs), a unique type of hierarchical micro-mesoporous composite material, namely, Beta-DMSNs (BD) was prepared through a nano-assembly method, which was utilized as superior supports for high-efficiency catalysts (NiMo/BD) for hydrodesulfurization (HDS) of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT). The controllable introduction of Beta nanocrystals endows the NiMo/BD catalysts with more acidic and catalytic active sites, and shows no influence on the dendritic morphology of the mesoporous supports, resulting in the remarkable HDS performance of NiMo/BD catalysts. Owing to the dendritic open channels, high surface area, abundant acidic sites and highly dispersed MoS2 active phases, the optimized NiMo/BD exhibited superior HDS activities of 99.1% and 98.3% for DBT and 4,6-DMDBT, respectively, with the optimal reaction rate constant of 3.0×10-7 mol g-1 s-1and 2.4×10-7 mol g-1 s-1, and with the turnover frequency of 5.9×10-4 s-1 and 4.8×10-4 s-1. Besides, the enhanced Brønsted acid and the synergistic effect of Brønsted & Lewis acid contributed to the superior isomerization selectivity for 4,6-DMDBT, which was conducive to its HDS.