Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
10244440 | Journal of Catalysis | 2005 | 10 Pages |
Abstract
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 m2âgâ1), medium (Ni2P/SiO2-M, 133 m2âgâ1), and high (Ni2P/SiO2-H, 208 m2âgâ1) specific surface areas. The activity was based on 240 μmol of active sites (as measured by CO chemisorption) loaded in the reactor and was measured at 573-643 K and 3.1 MPa. 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 catalyst with a conversion of 94% or the Ni2P/SiO2-L catalyst with a conversion of 76%. The order (H > M > L) correlated with the dispersion of the catalysts as measured from the respective CO uptakes for the samples (125 vs. 99 vs. 59 μmolâgâ1), and the Ni2P crystallite size as determined from X-ray diffraction (XRD) line-broadening measurements (6.5 vs. 7.8 vs. 10.1 nm). The higher surface area catalysts gave more of the 3-(3â²-methylcyclohexyl)toluene and 3,3â²-dimethylbicyclohexyl products, indicating that the small Ni2P crystallites favor desulfurization by the hydrogenation route. Increasing the reaction temperature from 573 to 643 K enhanced the HDS activities and at the same time gave more 3,3â²-dimethylbiphenyl product, indicating that high reaction temperatures favor the direct desulfurization route. Extended X-ray absorption fine structure (EXAFS) and elemental analysis measurements showed that the nickel phosphide was partially sulfided and probably formed a surface phosphosulfide phase in the course of the HDS reaction. The superior activity and stability of the Ni2P/SiO2-H catalyst was likely due to the better accessibility of the hindered 4,6-DMDBT molecule to the catalyst surface. The HDS reaction for this molecule is structure-sensitive.
Related Topics
Physical Sciences and Engineering
Chemical Engineering
Catalysis
Authors
Yuying Shu, Yong-Kul Lee, S. Ted Oyama,