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3 Advances in Hydrotreating Catalysts
There are several advances in hydrotreating catalysts in terms of activity, selectivity,
and stability due to better characterization tools and improved understanding of the
nature of active sites, support material, and the interaction between the active metals
and support. Use of additives or modifiers is found to enhance the catalytic activity
through altering the metal–support interactions, increasing the number of active
sites, etc. This is also supported by the choice of preparation methods. Stanislaus
et al. [2] have provided a comprehensive review of the effect of additives and
improvements in catalyst preparation techniques in HDT/HDS catalysts.
3.1 Additives/Modifiers and Their Effects
Additives or modifiers are certain elements/metals incorporated to the alumina support, especially to enhance the HDT/HDS catalyst performance through modification of the acidic and basic characteristics of the support material. Additives play an
important role in the modern HDT/HDS catalysts by means of the following:
• Influence metal–support interactions.
• Improve dispersion and distribution of active phases in the support.
• Enhance reducibility and sulfidability of the metals (Co, Ni, and Mo).
• Enhance the catalytic activity for HDS due to improved acidity characteristics.
• Decrease coking tendency of the catalyst.
• Improve thermal stability of the Al 2 O 3 support.
• Increase MoS 2 stacking and result in the formation of larger MoS 2 slabs.
Some of the additives that have been utilized in the HDT catalysts include phosphorous, boron, fluoride, silica, lanthanum, zinc, vanadium, and magnesium. Out of
these, phosphorous is the most important modifier used in commercial catalysts to
improve the hydrodenitrogenation (HDN) activity of NiMo-Al 2 O 3 catalysts [3].
Modification of support by addition of phosphorous was found to have beneficial
effects in HDT/HDS catalysts through better dispersion of active metal sulfide
phase, lower interaction between metal and support, higher Type II Ni (Co)-Mo-S
sites, lower coking, and increased MoS 2 stacking [4]. Fluoride and boron addition
was found to be effective in the formation of more active Type II Co-Mo-S or
Ni-Mo-S phases in the catalyst in order to improve the activity of the conventional
catalysts for the HDS of refractory sulfur species [5–7].
There is an optimal loading of additives during the preparation of hydrotreating
catalysts, which provides higher HDS and HDN activity. DeCanio and Weissman
[8] studied boron-modified commercial Ni-Mo/Al 2 O 3 hydrotreating catalysts using
FT-IR analysis of adsorbed NO and pyridine and using gas-oil HDS and HDN activities. Figure 1 shows the first-order rates of sulfur and nitrogen removal (Ks and Kn)
as a function of boron loading for a gas-oil feedstock. Although both reaction rates
Recent Advances in Hydrotreating/Hydrodesulfurization Catalysts: Part II—Catalyst…
3 Advances in Hydrotreating Catalysts
There are several advances in hydrotreating catalysts in terms of activity, selectivity,
and stability due to better characterization tools and improved understanding of the
nature of active sites, support material, and the interaction between the active metals
and support. Use of additives or modifiers is found to enhance the catalytic activity
through altering the metal–support interactions, increasing the number of active
sites, etc. This is also supported by the choice of preparation methods. Stanislaus
et al. [2] have provided a comprehensive review of the effect of additives and
improvements in catalyst preparation techniques in HDT/HDS catalysts.
3.1 Additives/Modifiers and Their Effects
Additives or modifiers are certain elements/metals incorporated to the alumina support, especially to enhance the HDT/HDS catalyst performance through modification of the acidic and basic characteristics of the support material. Additives play an
important role in the modern HDT/HDS catalysts by means of the following:
• Influence metal–support interactions.
• Improve dispersion and distribution of active phases in the support.
• Enhance reducibility and sulfidability of the metals (Co, Ni, and Mo).
• Enhance the catalytic activity for HDS due to improved acidity characteristics.
• Decrease coking tendency of the catalyst.
• Improve thermal stability of the Al 2 O 3 support.
• Increase MoS 2 stacking and result in the formation of larger MoS 2 slabs.
Some of the additives that have been utilized in the HDT catalysts include phosphorous, boron, fluoride, silica, lanthanum, zinc, vanadium, and magnesium. Out of
these, phosphorous is the most important modifier used in commercial catalysts to
improve the hydrodenitrogenation (HDN) activity of NiMo-Al 2 O 3 catalysts [3].
Modification of support by addition of phosphorous was found to have beneficial
effects in HDT/HDS catalysts through better dispersion of active metal sulfide
phase, lower interaction between metal and support, higher Type II Ni (Co)-Mo-S
sites, lower coking, and increased MoS 2 stacking [4]. Fluoride and boron addition
was found to be effective in the formation of more active Type II Co-Mo-S or
Ni-Mo-S phases in the catalyst in order to improve the activity of the conventional
catalysts for the HDS of refractory sulfur species [5–7].
There is an optimal loading of additives during the preparation of hydrotreating
catalysts, which provides higher HDS and HDN activity. DeCanio and Weissman
[8] studied boron-modified commercial Ni-Mo/Al 2 O 3 hydrotreating catalysts using
FT-IR analysis of adsorbed NO and pyridine and using gas-oil HDS and HDN activities. Figure 1 shows the first-order rates of sulfur and nitrogen removal (Ks and Kn)
as a function of boron loading for a gas-oil feedstock. Although both reaction rates
Recent Advances in Hydrotreating/Hydrodesulfurization Catalysts: Part II—Catalyst…