20
Studies using other support materials such as nanoporous alumino-silicate, e.g.,
MCM-41, Al-MCM-41, and SBA-15, and carbon supports were also reported in the
literature for CoMo- and NiMo-based HDS catalysts [56–60]. Nanoporous aluminosilica- based HDS catalysts are found to possess certain advantages such as high
surface area, high metal loading, high dispersion of active phase, and better feed
accessibility resulting in higher activity compared to conventional alumina-based
catalysts. Catalysts based on carbon support have been found to show high HDS
activity with decreased coke deactivation but have disadvantages due to rapid sintering of the active phase under reaction conditions and nonregenerability after deactivation. Although HDS catalysts using these new and novel supports were found to
perform better compared to conventional alumina-supported catalysts in laboratory
studies in terms of activity and selectivity, their application in industrial HDS/HDT
units requires extensive data generation and validation on their deactivation and
regeneration characteristics, economics of the formulations, etc.
Han et al. [61] synthesized γ-alumina with interconnected pore structure with the
presence of highly ordered mesopores within the walls of the macropore cages
using a sol-gel process using a mesoporous structure-directing agent. A CoMobased HDS catalyst was prepared using the interconnected meso-microporous alumina support and tested for the catalytic performance for HDS of DBT. The
CoMo-based catalyst supported on the interconnected γ-Al 2 O 3 exhibited higher
HDS activity compared to the catalyst prepared using conventional mesoporousbased commercial support due to better accessibility of the reactants to the active
sites. HDT catalysts prepared using mesoporous aluminas have found to be highly
active compared to conventional γ-alumina-based catalysts due to their better textural properties (surface area and pore volume), week acidity, improved metal dispersion, and lower Mo reduction tempertures. Badoga et al. [62] synthesized
NiMo-based catalysts using mesoporous alumina support and studied the performance for the HDT of heavy gas oil. Mesoporous alumina was synthesized using
pluronic P-123 as a structure-directing agent and aluminum isopropoxide as a precursor for aluminum with varied HNO 3 /H 2 O ratios ranging from 0 to 2. There are
changes in the textural properties and the structure of the NiMo catalysts prepared
using mesoporous aluminas with an increase in water content. NiMo catalysts prepared using synthesized mesoporous alumina with HNO 3 /H 2 O ratio of 0.6 showed
the highest HDS and HDN activity.
Li et al. [63] showed high HDS activity for 4,6-DMDBT for the NiMo catalyst
supported on tailored γ-Al 2 O 3 . The support was synthesized by hydrothermal treatment of pseudoboehmite. The high catalytic activity was attributed to their favorable crystal structure, better dispersion of Ni-Mo-S active phases, decrease in the
amount of hydroxyl groups, and tetrahedral cation vacancies.
Dong et al. [64] prepared mesoporous alumina microspheres comprising an
assembly of highly crystallized alumina nanorods using a template-free hydrothermal method with hierarchical pore structure and high specific surface area. Later,
bimetallic macro–mesoporous MoNi/Al 2 O 3 catalysts were prepared using the hierarchical alumina with better dispersion of the active Mo and Ni metals and higher
HDS and HDM activity compared to single pore catalysts.
G. Valavarasu and B. Ramachandrarao
Studies using other support materials such as nanoporous alumino-silicate, e.g.,
MCM-41, Al-MCM-41, and SBA-15, and carbon supports were also reported in the
literature for CoMo- and NiMo-based HDS catalysts [56–60]. Nanoporous aluminosilica- based HDS catalysts are found to possess certain advantages such as high
surface area, high metal loading, high dispersion of active phase, and better feed
accessibility resulting in higher activity compared to conventional alumina-based
catalysts. Catalysts based on carbon support have been found to show high HDS
activity with decreased coke deactivation but have disadvantages due to rapid sintering of the active phase under reaction conditions and nonregenerability after deactivation. Although HDS catalysts using these new and novel supports were found to
perform better compared to conventional alumina-supported catalysts in laboratory
studies in terms of activity and selectivity, their application in industrial HDS/HDT
units requires extensive data generation and validation on their deactivation and
regeneration characteristics, economics of the formulations, etc.
Han et al. [61] synthesized γ-alumina with interconnected pore structure with the
presence of highly ordered mesopores within the walls of the macropore cages
using a sol-gel process using a mesoporous structure-directing agent. A CoMobased HDS catalyst was prepared using the interconnected meso-microporous alumina support and tested for the catalytic performance for HDS of DBT. The
CoMo-based catalyst supported on the interconnected γ-Al 2 O 3 exhibited higher
HDS activity compared to the catalyst prepared using conventional mesoporousbased commercial support due to better accessibility of the reactants to the active
sites. HDT catalysts prepared using mesoporous aluminas have found to be highly
active compared to conventional γ-alumina-based catalysts due to their better textural properties (surface area and pore volume), week acidity, improved metal dispersion, and lower Mo reduction tempertures. Badoga et al. [62] synthesized
NiMo-based catalysts using mesoporous alumina support and studied the performance for the HDT of heavy gas oil. Mesoporous alumina was synthesized using
pluronic P-123 as a structure-directing agent and aluminum isopropoxide as a precursor for aluminum with varied HNO 3 /H 2 O ratios ranging from 0 to 2. There are
changes in the textural properties and the structure of the NiMo catalysts prepared
using mesoporous aluminas with an increase in water content. NiMo catalysts prepared using synthesized mesoporous alumina with HNO 3 /H 2 O ratio of 0.6 showed
the highest HDS and HDN activity.
Li et al. [63] showed high HDS activity for 4,6-DMDBT for the NiMo catalyst
supported on tailored γ-Al 2 O 3 . The support was synthesized by hydrothermal treatment of pseudoboehmite. The high catalytic activity was attributed to their favorable crystal structure, better dispersion of Ni-Mo-S active phases, decrease in the
amount of hydroxyl groups, and tetrahedral cation vacancies.
Dong et al. [64] prepared mesoporous alumina microspheres comprising an
assembly of highly crystallized alumina nanorods using a template-free hydrothermal method with hierarchical pore structure and high specific surface area. Later,
bimetallic macro–mesoporous MoNi/Al 2 O 3 catalysts were prepared using the hierarchical alumina with better dispersion of the active Mo and Ni metals and higher
HDS and HDM activity compared to single pore catalysts.
G. Valavarasu and B. Ramachandrarao