Structure-sensitivity of hydrodesulfurization of 4,6-dimethyldibenzothiophene over silica-supported nickel catalysts

The effect of surface area on the hydrodesulfurization (HDS) of 4,6-dimethyldibenzothiophene (4,6-DMDBT) was studied on a series of supported nickel phosphide catalysts of low (Ni2P/SiO2-L, 96 m2 g-1), medium (Ni2P/SiO2-M, 133 m2 g-1) and high (Ni2P/SiO2-H, 208 m2 g-1) specific surface areas. The best catalyst, Ni2P/SiO2-H, gave a steady-state conversion of 99+% at 613 K, which was higher than that of the Ni2P/SiO2-M (94%) or the Ni2P/SiO2-L (76%). The order (H > M > L) correlated with the dispersion of the catalysts as measured from CO uptakes (125 vs. 99 vs. 59 µmol g-1), and the Ni2P crystallite size as determined from X-ray diffraction (6.5 vs. 7.8 vs. 10.1 nm). Extended X-ray absorption fine structure (EXAFS) and elemental analysis measurements showed that the nickel phosphide was partially sulfided and formed a surface phosphosulfide phase in the HDS reaction. The HDS reaction for this molecule is structure-sensitive