58
The role of support is very important in the activity and selectivity of HDS catalysts since the supports can change the morphology of the active phase. Change in
support may result in the modulation of MSI. León et al. [70] studied NiW over
Al 2 O 3 -TiO 2 and ZrO 2 -TiO 2 mixed supports and showed their high catalytic activity
for light hydrocarbons. Li et al. [60] prepared Co/MoS 2 ± x catalysts with rich
defects and high stacking layers and studied for their HDS activity and hydrogenation selectivity for model gasoline. HDS selectivity was found to improve through
proper control of the crystal size of CoMo sulfide crystallites.
Xu et al. [61] studied the HDS activity of nickel yttrium-based catalysts supported on single-walled carbon nanotubes and reported better HDS activity for FCC
gasoline compared to monometallic catalysts owing to the small size of metal particles. Wang et al. [62] prepared CoMoS/Al 2 O 3 catalysts with different support pore
sizes and tested their performance for the hydrodesulfurization of FCC gasoline.
CoMoS/Al 2 O 3 catalysts prepared using micro- or mesoporous Al 2 O 3 showed higher
HDS activity and lower selectivity. Catalysts prepared using macroporous Al 2 O 3
showed higher selectivity due to tuning of the MoS 2 slabs and the weakening of the
internal diffusion resistance. The CoMoS/Al 2 O 3 catalyst prepared using the support
alumina with trimodal pore structure showed balanced HDS activity and selectivity
compared to the reference catalyst prepared using K- and P-modified Al 2 O 3 .
7.2 Selection of Hydrotreating Catalysts for Heavy Feedstocks
Such as Residue
Heavy feeds such as atmospheric and vacuum residue are characterized by increased
contents of heteroatoms (sulfur, nitrogen, and oxygen), metals (Ni and V), and
asphaltenes, and thus hydrotreating/hydrocracking of such residues require multiple
catalyst systems with different functionalities used in series. HDM catalysts are
used ahead of the hydrotreating/hydrocracking catalysts to remove the metals from
the feed and carry out disaggregation of asphaltenes and resins. The residue
hydrotreating catalysts are almost similar to those used for lighter fractions such as
diesel and VGO in terms of their chemical composition. In general, heavy feedstock
hydrotreating catalysts require very good hydrogenation activity to ensure better
decarbonization and improved catalyst life cycle by delaying coke formation.
Ni-Mo-based catalysts fare better due to their high hydrogenation activity for heavy
feedstock hydrotreating. Noble metal-based hydrotreating catalysts are not used for
heavy residue due to their high sulfur contents.
The physical properties (surface area, pore volume, pore size, pore size distribution) and shape of the catalysts play a crucial role in the hydrotreating of heavy residue due to the complex structure and composition of heavy molecules. The physical
properties of the hydrotreating catalysts vary between light and heavy feeds. Heavy
feed catalysts use smaller particles to ensure less diffusional path for the feed molecules to access the interior of the catalyst pores in order to ensure effective
G. Valavarasu and B. Ramachandrarao
The role of support is very important in the activity and selectivity of HDS catalysts since the supports can change the morphology of the active phase. Change in
support may result in the modulation of MSI. León et al. [70] studied NiW over
Al 2 O 3 -TiO 2 and ZrO 2 -TiO 2 mixed supports and showed their high catalytic activity
for light hydrocarbons. Li et al. [60] prepared Co/MoS 2 ± x catalysts with rich
defects and high stacking layers and studied for their HDS activity and hydrogenation selectivity for model gasoline. HDS selectivity was found to improve through
proper control of the crystal size of CoMo sulfide crystallites.
Xu et al. [61] studied the HDS activity of nickel yttrium-based catalysts supported on single-walled carbon nanotubes and reported better HDS activity for FCC
gasoline compared to monometallic catalysts owing to the small size of metal particles. Wang et al. [62] prepared CoMoS/Al 2 O 3 catalysts with different support pore
sizes and tested their performance for the hydrodesulfurization of FCC gasoline.
CoMoS/Al 2 O 3 catalysts prepared using micro- or mesoporous Al 2 O 3 showed higher
HDS activity and lower selectivity. Catalysts prepared using macroporous Al 2 O 3
showed higher selectivity due to tuning of the MoS 2 slabs and the weakening of the
internal diffusion resistance. The CoMoS/Al 2 O 3 catalyst prepared using the support
alumina with trimodal pore structure showed balanced HDS activity and selectivity
compared to the reference catalyst prepared using K- and P-modified Al 2 O 3 .
7.2 Selection of Hydrotreating Catalysts for Heavy Feedstocks
Such as Residue
Heavy feeds such as atmospheric and vacuum residue are characterized by increased
contents of heteroatoms (sulfur, nitrogen, and oxygen), metals (Ni and V), and
asphaltenes, and thus hydrotreating/hydrocracking of such residues require multiple
catalyst systems with different functionalities used in series. HDM catalysts are
used ahead of the hydrotreating/hydrocracking catalysts to remove the metals from
the feed and carry out disaggregation of asphaltenes and resins. The residue
hydrotreating catalysts are almost similar to those used for lighter fractions such as
diesel and VGO in terms of their chemical composition. In general, heavy feedstock
hydrotreating catalysts require very good hydrogenation activity to ensure better
decarbonization and improved catalyst life cycle by delaying coke formation.
Ni-Mo-based catalysts fare better due to their high hydrogenation activity for heavy
feedstock hydrotreating. Noble metal-based hydrotreating catalysts are not used for
heavy residue due to their high sulfur contents.
The physical properties (surface area, pore volume, pore size, pore size distribution) and shape of the catalysts play a crucial role in the hydrotreating of heavy residue due to the complex structure and composition of heavy molecules. The physical
properties of the hydrotreating catalysts vary between light and heavy feeds. Heavy
feed catalysts use smaller particles to ensure less diffusional path for the feed molecules to access the interior of the catalyst pores in order to ensure effective
G. Valavarasu and B. Ramachandrarao