43
readily, resulting in fast sulfidation at 20 bar H 2 /H 2 S pressure at 350 °C. The intrinsic activity of the catalysts measured in terms of turnover frequency for catalysts
prepared using additives was substantially higher than prepared without using additives, as shown by the highest TOF value of 0.028 s
−1
for CoMo-CA.
Chen et al. [23] showed that modification of HDS catalysts using organic additives (ethylene glycol and CA) resulted in the reduction of MoS 2 slab length and
increased stacking due to change in MSI. Temperature is one of the key factors in
the preparation of unsupported MoS 2 nanocatalysts, which affects the hydrotreating
activity. Initial temperature and synthesis temperature both are found to play an
important role in tuning the morphology, crystalline nature, and catalyst properties
and eventually in the catalytic activity. Zhang et al. [24] synthesized unsupported
MoS 2 catalysts using the hydrothermal method at different initial and synthesis temperatures and tested for their HDS and HDN activities using light cycle oil as feedstock. Higher synthesis temperature and initial temperature favored higher HDS and
HDN activities due to curved/shortened MoS 2 slabs and enhanced crystallinity. In
the CAT-20-200, the initial temperature is mentioned as 20 °C and the synthesis
temperature is 200 °C.
Being one of the catalyst preparation methods, chemical vapor deposition (CVD)
was found to improve the formation of highly active Co-Mo-S active phases in a
selective manner resulting in substantially high catalytic activity compared to CoMo
catalysts prepared using the impregnation method [25, 26].
Although literature is replete with the use of several new catalyst preparation
techniques such as CVD and incorporation of other modifiers/additives into the
hydrotreating catalysts for obtaining highly active catalytic sites, most of these
methods/materials are not commercially proven yet, and these are still in the development stage in the laboratory. Further research work is needed to validate the findings in terms of activity, selectivity, and stability characteristics and utilize these
novel methods and materials in the preparation of economically viable catalysts for
HDS/HDT application.
Liu et al. [27] prepared highly active HDS catalysts using PVP-assisted synthesis
of both supported and unsupported NiMo oxide catalysts with varying PVP contents and showed high activity for the HDS of DBT due to the formation of favorable active phases such as MoS 2 and Ni 3 S 2 nanoparticles on the sulfided catalyst.
Wang et al. [28] synthesized mesoporous γ-Al 2 O 3 support material with different
textural properties and acidities using AlCl 3 ·6H 2 O as an aluminum source and polyethylene glycol as a mesostructure-directing agent by tuning the hydrothermal
aging temperature. Two-step incipient wetness impregnation method was subsequently used to prepare NiMo/γ-Al 2 O 3 catalysts and studied for their HDS performance using model compounds. Catalyst synthesized at an aging temperature of
363 K showed the highest HDS activity due to favorable textural properties, acidity,
and MSI apart from optimal metal dispersion, sulfidation, and MoS 2 stacking. Also,
this catalyst resulted in the highest HYD/DDS ratio for the HDS of 4,6-DMDBT,
indicating the predominance of the hydrogenation pathway over DDS for the HDS
reaction. Wang et al. [29] synthesized mesoporous alumina with different crystal
forms from the boehmite sol and used them as supports for bimetallic sulfided NiMo
Recent Advances in Hydrotreating/Hydrodesulfurization Catalysts: Part II—Catalyst…
readily, resulting in fast sulfidation at 20 bar H 2 /H 2 S pressure at 350 °C. The intrinsic activity of the catalysts measured in terms of turnover frequency for catalysts
prepared using additives was substantially higher than prepared without using additives, as shown by the highest TOF value of 0.028 s
−1
for CoMo-CA.
Chen et al. [23] showed that modification of HDS catalysts using organic additives (ethylene glycol and CA) resulted in the reduction of MoS 2 slab length and
increased stacking due to change in MSI. Temperature is one of the key factors in
the preparation of unsupported MoS 2 nanocatalysts, which affects the hydrotreating
activity. Initial temperature and synthesis temperature both are found to play an
important role in tuning the morphology, crystalline nature, and catalyst properties
and eventually in the catalytic activity. Zhang et al. [24] synthesized unsupported
MoS 2 catalysts using the hydrothermal method at different initial and synthesis temperatures and tested for their HDS and HDN activities using light cycle oil as feedstock. Higher synthesis temperature and initial temperature favored higher HDS and
HDN activities due to curved/shortened MoS 2 slabs and enhanced crystallinity. In
the CAT-20-200, the initial temperature is mentioned as 20 °C and the synthesis
temperature is 200 °C.
Being one of the catalyst preparation methods, chemical vapor deposition (CVD)
was found to improve the formation of highly active Co-Mo-S active phases in a
selective manner resulting in substantially high catalytic activity compared to CoMo
catalysts prepared using the impregnation method [25, 26].
Although literature is replete with the use of several new catalyst preparation
techniques such as CVD and incorporation of other modifiers/additives into the
hydrotreating catalysts for obtaining highly active catalytic sites, most of these
methods/materials are not commercially proven yet, and these are still in the development stage in the laboratory. Further research work is needed to validate the findings in terms of activity, selectivity, and stability characteristics and utilize these
novel methods and materials in the preparation of economically viable catalysts for
HDS/HDT application.
Liu et al. [27] prepared highly active HDS catalysts using PVP-assisted synthesis
of both supported and unsupported NiMo oxide catalysts with varying PVP contents and showed high activity for the HDS of DBT due to the formation of favorable active phases such as MoS 2 and Ni 3 S 2 nanoparticles on the sulfided catalyst.
Wang et al. [28] synthesized mesoporous γ-Al 2 O 3 support material with different
textural properties and acidities using AlCl 3 ·6H 2 O as an aluminum source and polyethylene glycol as a mesostructure-directing agent by tuning the hydrothermal
aging temperature. Two-step incipient wetness impregnation method was subsequently used to prepare NiMo/γ-Al 2 O 3 catalysts and studied for their HDS performance using model compounds. Catalyst synthesized at an aging temperature of
363 K showed the highest HDS activity due to favorable textural properties, acidity,
and MSI apart from optimal metal dispersion, sulfidation, and MoS 2 stacking. Also,
this catalyst resulted in the highest HYD/DDS ratio for the HDS of 4,6-DMDBT,
indicating the predominance of the hydrogenation pathway over DDS for the HDS
reaction. Wang et al. [29] synthesized mesoporous alumina with different crystal
forms from the boehmite sol and used them as supports for bimetallic sulfided NiMo
Recent Advances in Hydrotreating/Hydrodesulfurization Catalysts: Part II—Catalyst…