25
HDN of indole and quinoline, and HDS of DBT and 4,6-DMDBT due to moderate
acidity and other favorable structural and morphological characteristics.
Zheng et al. [78] prepared novel composite support β-SBA-16 using both β zeolite and SBA-16 and showed higher hydrodesulfurization activity for the NiMo/β- -
SBA- 16 catalyst compared to Al-modified SBA-16 and the traditional
Al 2 O 3 -supported catalysts due to higher acidity and better synergy between Brønsted
and Lewis acid sites. They also confirmed the high activity based on DFT calculations. Wang et al. [79] prepared mesoporous Al-SBA-16 as support for NiMo-based
catalysts and showed higher isomerization activity for the HDS of DBT and
4.6-DMDBT.
Asadi et al. [80] prepared NiMo catalysts with composite USY/γ-Al 2 O 3 supports
and studied the effect of active phase and compositions of support on the activity.
The most active composite catalyst contained 10 wt% USY zeolite, loaded with
18 wt% Ni and Mo oxides with Ni/(Ni + Mo) and EDTA/Ni molar ratios of 0.417
and 2, respectively, and the HDS results were validated using model and experiments.
Although the mixed oxide-based bifunctional catalysts possess advantages in
terms of high surface area and good acid–base properties for promoting HDS of
sterically hindered sulfur compounds, they are prone to rapid deactivation at the
acid sites due to coking and poisoning by basic nitrogen compounds. Although
acidic supports were reported to be effective for HDS of refractory sulfur compounds, they have certain issues such as (a) difficulty in the impregnation and dispersion of active phases on the support surface and (b) pore size limitations, which
may restrict the accessibility of bulky reactant molecules such as 4,6-DMDBT. Also,
the acidic supports may promote hydrocracking reactions that will result in loss of
valuable hydrocarbon yields. Strong acid site density and Brönsted acidity of zeolite
containing catalysts could cause rapid deactivation by formation of coke [81] apart
from the formation of lighter products resulting in yield loss.
6.3 Unsupported Catalysts
Unsupported transition metal-based catalysts such as sulfides, carbides, and nitrides
of cobalt, molybdenum, and tungsten and also metal phosphides were studied in the
literature as promising catalysts for HDT/HDS reactions. Unsupported mixed sulfides prepared using the same family of metals as that of supported catalysts were
reported to exhibit high activity for HDS, HDN, and HDA compared to the supported catalysts [82]. Hermann et al. [83] studied the unsupported RuS 2 , Rh 2 S 3 , and
NbS 3 for their HDS performance and found that these catalysts possessed higher
desulfurization activity compared to Co-Ni and No-W metal sulfides. Unsupported
trimetallic catalysts such as Ni-Mo-W sulfide were found to exhibit about three
times higher activity for HDS compared to Al 2 O 3 -supported NiMo and CoMo catalysts [84–86]. Such unsupported trimetallic catalysts were successfully used in
commercial hydrotreaters for deep HDS of diesel fraction by Albamarle using the
trade name NEBULA. Although other forms of unsupported catalysts such as metal
Recent Advances in Hydrotreating/Hydrodesulfurization Catalysts: Part I: Nature…
HDN of indole and quinoline, and HDS of DBT and 4,6-DMDBT due to moderate
acidity and other favorable structural and morphological characteristics.
Zheng et al. [78] prepared novel composite support β-SBA-16 using both β zeolite and SBA-16 and showed higher hydrodesulfurization activity for the NiMo/β- -
SBA- 16 catalyst compared to Al-modified SBA-16 and the traditional
Al 2 O 3 -supported catalysts due to higher acidity and better synergy between Brønsted
and Lewis acid sites. They also confirmed the high activity based on DFT calculations. Wang et al. [79] prepared mesoporous Al-SBA-16 as support for NiMo-based
catalysts and showed higher isomerization activity for the HDS of DBT and
4.6-DMDBT.
Asadi et al. [80] prepared NiMo catalysts with composite USY/γ-Al 2 O 3 supports
and studied the effect of active phase and compositions of support on the activity.
The most active composite catalyst contained 10 wt% USY zeolite, loaded with
18 wt% Ni and Mo oxides with Ni/(Ni + Mo) and EDTA/Ni molar ratios of 0.417
and 2, respectively, and the HDS results were validated using model and experiments.
Although the mixed oxide-based bifunctional catalysts possess advantages in
terms of high surface area and good acid–base properties for promoting HDS of
sterically hindered sulfur compounds, they are prone to rapid deactivation at the
acid sites due to coking and poisoning by basic nitrogen compounds. Although
acidic supports were reported to be effective for HDS of refractory sulfur compounds, they have certain issues such as (a) difficulty in the impregnation and dispersion of active phases on the support surface and (b) pore size limitations, which
may restrict the accessibility of bulky reactant molecules such as 4,6-DMDBT. Also,
the acidic supports may promote hydrocracking reactions that will result in loss of
valuable hydrocarbon yields. Strong acid site density and Brönsted acidity of zeolite
containing catalysts could cause rapid deactivation by formation of coke [81] apart
from the formation of lighter products resulting in yield loss.
6.3 Unsupported Catalysts
Unsupported transition metal-based catalysts such as sulfides, carbides, and nitrides
of cobalt, molybdenum, and tungsten and also metal phosphides were studied in the
literature as promising catalysts for HDT/HDS reactions. Unsupported mixed sulfides prepared using the same family of metals as that of supported catalysts were
reported to exhibit high activity for HDS, HDN, and HDA compared to the supported catalysts [82]. Hermann et al. [83] studied the unsupported RuS 2 , Rh 2 S 3 , and
NbS 3 for their HDS performance and found that these catalysts possessed higher
desulfurization activity compared to Co-Ni and No-W metal sulfides. Unsupported
trimetallic catalysts such as Ni-Mo-W sulfide were found to exhibit about three
times higher activity for HDS compared to Al 2 O 3 -supported NiMo and CoMo catalysts [84–86]. Such unsupported trimetallic catalysts were successfully used in
commercial hydrotreaters for deep HDS of diesel fraction by Albamarle using the
trade name NEBULA. Although other forms of unsupported catalysts such as metal
Recent Advances in Hydrotreating/Hydrodesulfurization Catalysts: Part I: Nature…