16
application in the refining industry. Studies have been performed to investigate the
promotion effect of noble metals such as Pt, Pd, Ru, Rh, and Ir with MoS 2 -based
catalysts supported on alumina using decomposition and impregnation of bimetallic
molecular clusters on the HDS, HDN, and HYD activities of a feedstock containing
DBT, indole, and naphthalene [26]. The hydrotreating activities followed the order:
Mo 3 Ir > Mo 3 Rh > Mo 3 Ru > Mo 3 Pt > Mo 3 Pd. Although Mo 3 Ir- and Mo 3 Rh-based
catalysts were found to have strong synergy and higher HDT activity, their performance is inferior compared to the Mo 3 Ni catalyst.
The effect of the nature of catalytic active phases on the extent of HDS and olefin
saturation reactions will be helpful in the development of highly selective FCC gasoline HDS catalysts that require selective removal of sulfur compounds with minimum octane loss. Huang et al. [27] investigated the nature of CoMoS and MoS 2
active phases co-existing on sulfided CoMo/Al 2 O 3 catalysts for the selective HDS of
gasoline. They prepared two series of catalysts: CoMo/Al 2 O 3 catalysts with different EDTA/Co molar ratios and EDTA containing CoMo/Al 2 O 3 catalysts with different Co contents. HDS activity of the sulfided CoMo/Al 2 O 3 catalysts was primarily
enhanced by the high concentration of CoMoS phases, while olefin hydrogenation
activity was improved by high concentration of MoS 2 active phases.
Grønborg et al. [28] used advanced characterization tools such as STM to study
the cluster shapes and edge transformations in MoS 2 structure and promoted
CoMoS-type HDS catalysts under reducing conditions both through experimental
observations and DFT predictions. It was shown that the reduced catalyst clusters
were terminated with a fractional coverage of sulfur, representing the catalyst in its
active state. The presence of catalytically active S-H groups was found on the
Co-promoted edge sites by adsorption of a proton-accepting molecular marker.
There is a new trend in using DFT simulations for the identification of active sites
and complex reaction pathways in the hydrotreating catalysis due to its industrial
importance. DFT studies will be useful to get new insights into the nature of active
sites, and this knowledge could be used in the design of efficient HDT catalysts for
the production of ULSD. Li et al. [29] utilized DFT calculations using a dispersion
correction method to construct a novel corner site model of MoS 2 and investigate the
DDS and HYD pathways. Based on mechanistic and energetic analysis, it was found
that the C-S bond cleavage had the highest energy barrier for both reaction DDS and
HYD pathways and DDS is more favorable on corner sites of MoS 2 compared to
HYD pathway. They also compared the activation energies of both reaction pathways on four different active sites (Mo edge, S edge, CoMoS edge, and corner) for
the HDS of thiophene and concluded that corner sites play a major role in the HDS
of thiophenic sulfur compounds through mostly DDS pathway.
6.2 Supports or Carriers
Support material with optimized physicochemical characteristics is the prime prerequisite for the preparation of good HDT catalysts with high activity and long-term
stability. Supports provide the required surface area for dispersion of metals. The
G. Valavarasu and B. Ramachandrarao
application in the refining industry. Studies have been performed to investigate the
promotion effect of noble metals such as Pt, Pd, Ru, Rh, and Ir with MoS 2 -based
catalysts supported on alumina using decomposition and impregnation of bimetallic
molecular clusters on the HDS, HDN, and HYD activities of a feedstock containing
DBT, indole, and naphthalene [26]. The hydrotreating activities followed the order:
Mo 3 Ir > Mo 3 Rh > Mo 3 Ru > Mo 3 Pt > Mo 3 Pd. Although Mo 3 Ir- and Mo 3 Rh-based
catalysts were found to have strong synergy and higher HDT activity, their performance is inferior compared to the Mo 3 Ni catalyst.
The effect of the nature of catalytic active phases on the extent of HDS and olefin
saturation reactions will be helpful in the development of highly selective FCC gasoline HDS catalysts that require selective removal of sulfur compounds with minimum octane loss. Huang et al. [27] investigated the nature of CoMoS and MoS 2
active phases co-existing on sulfided CoMo/Al 2 O 3 catalysts for the selective HDS of
gasoline. They prepared two series of catalysts: CoMo/Al 2 O 3 catalysts with different EDTA/Co molar ratios and EDTA containing CoMo/Al 2 O 3 catalysts with different Co contents. HDS activity of the sulfided CoMo/Al 2 O 3 catalysts was primarily
enhanced by the high concentration of CoMoS phases, while olefin hydrogenation
activity was improved by high concentration of MoS 2 active phases.
Grønborg et al. [28] used advanced characterization tools such as STM to study
the cluster shapes and edge transformations in MoS 2 structure and promoted
CoMoS-type HDS catalysts under reducing conditions both through experimental
observations and DFT predictions. It was shown that the reduced catalyst clusters
were terminated with a fractional coverage of sulfur, representing the catalyst in its
active state. The presence of catalytically active S-H groups was found on the
Co-promoted edge sites by adsorption of a proton-accepting molecular marker.
There is a new trend in using DFT simulations for the identification of active sites
and complex reaction pathways in the hydrotreating catalysis due to its industrial
importance. DFT studies will be useful to get new insights into the nature of active
sites, and this knowledge could be used in the design of efficient HDT catalysts for
the production of ULSD. Li et al. [29] utilized DFT calculations using a dispersion
correction method to construct a novel corner site model of MoS 2 and investigate the
DDS and HYD pathways. Based on mechanistic and energetic analysis, it was found
that the C-S bond cleavage had the highest energy barrier for both reaction DDS and
HYD pathways and DDS is more favorable on corner sites of MoS 2 compared to
HYD pathway. They also compared the activation energies of both reaction pathways on four different active sites (Mo edge, S edge, CoMoS edge, and corner) for
the HDS of thiophene and concluded that corner sites play a major role in the HDS
of thiophenic sulfur compounds through mostly DDS pathway.
6.2 Supports or Carriers
Support material with optimized physicochemical characteristics is the prime prerequisite for the preparation of good HDT catalysts with high activity and long-term
stability. Supports provide the required surface area for dispersion of metals. The
G. Valavarasu and B. Ramachandrarao