Study on hydrodesulfurization mechanism of 4,6-dimethyldibenzothiophene I. Catalytic behavior of NiW-based catalysts

NiW-based catalysts supported on gamma-Al2O3, amorphous silica-alumina and rare earth HY zeolite-containing gamma-Al2O3, respectively, were prepared by incipient wetness co-impregnation method. Hydrodesulfurization (HDS) of 4, 6-dimethyldibenzothiophene (DMDBT) was performed in a continuous flow microreactor under the conditions of p = 4.14 MPa and theta = 270 similar to 330 degreesC. The DMDBT was dissolved in decane to obtain 0.1% sulfur solution. The liquid products were analyzed by GC-FID equipped with a capillary column. The results showed that the NiW-based catalysts exhibit better performance for desulfurization and hydrogenation of DMDBT, and the main product is dimethylcyclohexylbenzene with selectivity of 59.4%. The enhancement of hydrogenation activity is the most effective way to increase HDS activity. The enhancement of support acidity favors direct desulfurization and leads to a small amount of cracking products. NiW catalysts on acidic supports can transform DMDBT into isomers by migrating methyl groups adjacent to the S atom, which also favors desulfurization of DMDBT. However, their hydrogenation activity is inferior to that of alumina-supported sample. Based on the experimental results, the different reaction pathways of DMDBT transformation were proposed.