21
Peng et al. [65] deposited cobalt and molybdenum nanoparticles on the mesoporous γ-Al 2 O 3 with the addition of an organic compound and found that the catalyst
was easily reduced with the organic compound resulting in better sulfidation degree
and enhanced HDS activity. This catalyst was commercially tested for diesel HDS
application to produce ULSD and also reported to be highly stable.
Tang et al. [66] prepared CoMo-based HDS catalysts using mesoporous mordenite nanofibers with bundle structure as a support material. The mesoporous catalyst
showed very high HDS activity for HDS of 4,6-DMDBT (99.1%) compared to a
conventional γ-alumina-supported CoMo catalyst (61.5%). The high activity was
ascribed to the migration of spillover hydrogen from micropores to CoMo active
sites present in the mesopores.
Dugulan et al. [67] investigated the sulfiding behavior and hydrotreating performance of CoMo- and NiMo-based HDT catalysts supported on carbon. Although
structural evolution and active phase transition are similar for CoMo/C and CoMo/
Al 2 O 3 catalysts, some sintering was observed for carbon-supported catalysts. In the
case of the NiMo/C catalyst, strong adsorption of dibenzthiophene, quinoline, and
polyaromatics in comparison with NiMo/alumina resulted in significantly high
HDS and HDN activity for DBT and quinolone, respectively. However, the NiMo/C
catalyst showed poor activity for the HDT of heavy gas oil due to competitive
adsorption of polyaromatics along with sulfur and nitrogen compounds on the catalytic active sites.
AL-Hammadi et al. [68] prepared a novel carbon-nanofiber-doped alumina as a
support material for the CoMo (AlCNFMoCo)-based catalyst and compared its
HDS activity with the alumina-supported CoMo (AlMoCo) catalyst for the HDS of
DBT in a batch reactor. They showed that the HDS activity of carbon-nanofiberdoped alumina catalysts is better than conventional catalysts due to high mesoporous surface area, better dispersion of active metals on the support, and good textural
properties. Also, they proposed DDS as the predominant reaction mechanism for
the carbon-nanofiber-doped alumina catalyst compared to the HYD pathway based
on GC-MS analysis of reaction products. However, long-term stability of these catalysts and performance using actual feedstock need to be assessed.
HDT catalysts prepared using silica-modified alumina supports were also investigated through different synthesis methods to enhance the activity for the removal
of refractory sulfur compounds through incorporation of moderate acidity to the
catalyst. Silica incorporated in alumina structure modifies the catalyst properties
and performance depending upon the method of incorporation. Rayo et al. [69]
prepared NiMo-based HDT catalysts using 5 wt% Si in alumina by two different
methods, one by incorporation of Si into boehmite (NiMo/Si-Al), followed by drying and calcination. In another method, Si was incorporated into the surface of
already calcined alumina (NiMo/Si/Al), which resulted in different surface structures of the Si oxide layer. The performance of these two catalysts was different for
the HDS of partially hydrotreated Maya crude oil and cumene hydrocracking applications. The highest activity for HDT of refractory sulfur compounds present in the
hydrotreated Maya crude oil/diesel blend feedstock was achieved using the catalyst
Recent Advances in Hydrotreating/Hydrodesulfurization Catalysts: Part I: Nature…
Peng et al. [65] deposited cobalt and molybdenum nanoparticles on the mesoporous γ-Al 2 O 3 with the addition of an organic compound and found that the catalyst
was easily reduced with the organic compound resulting in better sulfidation degree
and enhanced HDS activity. This catalyst was commercially tested for diesel HDS
application to produce ULSD and also reported to be highly stable.
Tang et al. [66] prepared CoMo-based HDS catalysts using mesoporous mordenite nanofibers with bundle structure as a support material. The mesoporous catalyst
showed very high HDS activity for HDS of 4,6-DMDBT (99.1%) compared to a
conventional γ-alumina-supported CoMo catalyst (61.5%). The high activity was
ascribed to the migration of spillover hydrogen from micropores to CoMo active
sites present in the mesopores.
Dugulan et al. [67] investigated the sulfiding behavior and hydrotreating performance of CoMo- and NiMo-based HDT catalysts supported on carbon. Although
structural evolution and active phase transition are similar for CoMo/C and CoMo/
Al 2 O 3 catalysts, some sintering was observed for carbon-supported catalysts. In the
case of the NiMo/C catalyst, strong adsorption of dibenzthiophene, quinoline, and
polyaromatics in comparison with NiMo/alumina resulted in significantly high
HDS and HDN activity for DBT and quinolone, respectively. However, the NiMo/C
catalyst showed poor activity for the HDT of heavy gas oil due to competitive
adsorption of polyaromatics along with sulfur and nitrogen compounds on the catalytic active sites.
AL-Hammadi et al. [68] prepared a novel carbon-nanofiber-doped alumina as a
support material for the CoMo (AlCNFMoCo)-based catalyst and compared its
HDS activity with the alumina-supported CoMo (AlMoCo) catalyst for the HDS of
DBT in a batch reactor. They showed that the HDS activity of carbon-nanofiberdoped alumina catalysts is better than conventional catalysts due to high mesoporous surface area, better dispersion of active metals on the support, and good textural
properties. Also, they proposed DDS as the predominant reaction mechanism for
the carbon-nanofiber-doped alumina catalyst compared to the HYD pathway based
on GC-MS analysis of reaction products. However, long-term stability of these catalysts and performance using actual feedstock need to be assessed.
HDT catalysts prepared using silica-modified alumina supports were also investigated through different synthesis methods to enhance the activity for the removal
of refractory sulfur compounds through incorporation of moderate acidity to the
catalyst. Silica incorporated in alumina structure modifies the catalyst properties
and performance depending upon the method of incorporation. Rayo et al. [69]
prepared NiMo-based HDT catalysts using 5 wt% Si in alumina by two different
methods, one by incorporation of Si into boehmite (NiMo/Si-Al), followed by drying and calcination. In another method, Si was incorporated into the surface of
already calcined alumina (NiMo/Si/Al), which resulted in different surface structures of the Si oxide layer. The performance of these two catalysts was different for
the HDS of partially hydrotreated Maya crude oil and cumene hydrocracking applications. The highest activity for HDT of refractory sulfur compounds present in the
hydrotreated Maya crude oil/diesel blend feedstock was achieved using the catalyst
Recent Advances in Hydrotreating/Hydrodesulfurization Catalysts: Part I: Nature…