41
impregnating of a support had a negative influence on catalytic activity due to the
formation of CoAl 2 O 4 compounds and reduced content of promoter cobalt in the
active phase.
Fan et al. [19] proposed a hydrothermal deposition method assisted by cetyltrimethylammonium bromide and fluorine for modulating the morphology of supported metal nanoparticles in NiWF/Al 2 O 3 HDS catalysts. This catalyst synthesis
approach was found to promote the dispersion of W by bridging and anchoring the
metal nanoparticles on the surface of fluorinated alumina support and also lowered
subsequent agglomeration of W during calcination. This method was reported to
provide higher HDS activity compared to the conventional impregnation method
due to improved metal dispersion, higher promotion effects, and more accessible
Ni-W-S active sites.
3.2 Catalyst Preparation Methods
Hydrotreating catalysts are prepared by impregnation of active metals (Mo and Co
or Ni) on the surface of the support material such as alumina. The metal components
are used in the form of aqueous solutions to form respective metal ions that will be
subsequently deposited on the surface of the support using different impregnation
techniques. The following are the widely used impregnation techniques for the
preparation of hydrotreating catalysts:
• Incipient wetness impregnation.
• Equilibrium adsorption.
In the first method, the support is contacted with a solution containing the metal
precursor salts in a predetermined volume of water sufficient to fill the pores. In the
second method, molybdenum from an aqueous solution of ammonium heptamolybdate is adsorbed on the support over an extended period of time till equilibrium is
reached and followed by the filtration of the leftover liquid [2]. Modified impregnating methods through the addition of chelating agents or complexing agents to the
impregnating solution were found to be advantageous in improving the activity of
HDS catalysts through the following:
• Formation of a maximum number of Type II Co-Mo-S and Ni-Mo-S active
phases with very high selectivity.
• Enhanced reducibility of molybdenum.
• Reducing the strong interaction between support and metal.
• Improved dispersion of metals over the support.
• Higher promotion effect resulting in a strong synergy between Co(Ni) and Mo
sulfides.
Chelating or complexing agents are beneficial in delaying the sulfidation temperature of promoter metals (Co or Ni), which otherwise start sulfiding at lower
temperatures compared to Mo resulting in poor sulfidation of the catalyst with
Recent Advances in Hydrotreating/Hydrodesulfurization Catalysts: Part II—Catalyst…
impregnating of a support had a negative influence on catalytic activity due to the
formation of CoAl 2 O 4 compounds and reduced content of promoter cobalt in the
active phase.
Fan et al. [19] proposed a hydrothermal deposition method assisted by cetyltrimethylammonium bromide and fluorine for modulating the morphology of supported metal nanoparticles in NiWF/Al 2 O 3 HDS catalysts. This catalyst synthesis
approach was found to promote the dispersion of W by bridging and anchoring the
metal nanoparticles on the surface of fluorinated alumina support and also lowered
subsequent agglomeration of W during calcination. This method was reported to
provide higher HDS activity compared to the conventional impregnation method
due to improved metal dispersion, higher promotion effects, and more accessible
Ni-W-S active sites.
3.2 Catalyst Preparation Methods
Hydrotreating catalysts are prepared by impregnation of active metals (Mo and Co
or Ni) on the surface of the support material such as alumina. The metal components
are used in the form of aqueous solutions to form respective metal ions that will be
subsequently deposited on the surface of the support using different impregnation
techniques. The following are the widely used impregnation techniques for the
preparation of hydrotreating catalysts:
• Incipient wetness impregnation.
• Equilibrium adsorption.
In the first method, the support is contacted with a solution containing the metal
precursor salts in a predetermined volume of water sufficient to fill the pores. In the
second method, molybdenum from an aqueous solution of ammonium heptamolybdate is adsorbed on the support over an extended period of time till equilibrium is
reached and followed by the filtration of the leftover liquid [2]. Modified impregnating methods through the addition of chelating agents or complexing agents to the
impregnating solution were found to be advantageous in improving the activity of
HDS catalysts through the following:
• Formation of a maximum number of Type II Co-Mo-S and Ni-Mo-S active
phases with very high selectivity.
• Enhanced reducibility of molybdenum.
• Reducing the strong interaction between support and metal.
• Improved dispersion of metals over the support.
• Higher promotion effect resulting in a strong synergy between Co(Ni) and Mo
sulfides.
Chelating or complexing agents are beneficial in delaying the sulfidation temperature of promoter metals (Co or Ni), which otherwise start sulfiding at lower
temperatures compared to Mo resulting in poor sulfidation of the catalyst with
Recent Advances in Hydrotreating/Hydrodesulfurization Catalysts: Part II—Catalyst…