Regulating the coordination environment of surface alumina on NiMo/Al2O3 to enhance ultra-deep hydrodesulfurization of diesel

Herein, a set of NiMo/Al2O3 catalysts with distinct coordination state of surface alumina were design and prepared by a facile calcination strategy. Various characterization methods were employed to analyze the structural properties of NiMo/Al2O3 catalysts, and the catalytic performances of corresponding catalysts were tested for hydrodesulfurization (HDS) of 4,6-dimethyldibenzothiophene (4,6-DMDBT). The results indicate that the synthesized samples show uniform specific surface area (130 m2·g−1) and pore size (3.5 nm), but varying penta-coordinated aluminum content, which significantly influences the NiMo/Al2O3 catalysts' surface acidity. Therein, NiMo/Al2O3-600 prepared by calcination at 600 °C exhibits the highest ratio of penta-coordinated aluminum species, which endows more abundant Brønsted acid than that of tetra- and hexa-coordinated aluminum counterparts, thereby substantially promoting the isomerization and direct desulfurization pathways of 4,6-DMDBT HDS, and thereafter considerably boosting the HDS performance of NiMo/Al2O3-600 with 94.5 % 4,6-DMDBT conversion, which is notably higher than that of NiMo/Al2O3-500 (74.4 %) and NiMo/Al2O3-700 (62.7 %).