18
of stacking of MoS 2 and Co-Mo-S structures. Modification of γ-Al 2 O 3 support
through incorporation of zeolites and some metal oxides was also attempted to promote the desulfurization of sterically hindered sulfur species such as alkyl DBTs
through isomerization and dealkylation. Some of these mixed oxide supports tested
for HDS applications include Al 2 O 3 -SiO 2 , Al 2 O 3 -TiO 2 , Al 2 O 3 -ZrO 2 , and Al 2 O 3 -P 2 O 5 .
Other mixed supports include Al 2 O 3 -HY and Al 2 O 3 -F.
Hydrodesulfurization of model compounds (DBT and its derivatives) and
straight-run gas oils over mixed metal oxide TiO 2 -Al 2 O 3 showed much higher activity for desulfurization compared to supported alumina-based HDT catalysts [14,
40–42]. Incorporation of Ti in the different support materials such as alumina,
SBA-15, and MCM-41 was found to show higher HDS performance for metal sulfide catalysts compared to Ti-free supports due to weak Mo-S interaction and creation of more sulfur vacancies due to reduction of Ti species to Ti3+ species under
HDS reaction conditions and subsequent transfer of spare electrons into the Mo3d
conduction band [43–47].
Fujikawa et al. [48] prepared CoMo HDS catalyst for the production of ULSD
using phosphorous and citric acid as additives on HY-Al 2 O 3 support and showed
three times higher HDS activity compared to conventional CoMoP/Al 2 O 3 catalyst
for the HDS of straight-run light gas oil feedstocks under industrial HDT conditions. Ding et al. [49] studied hydrotreating of LCO using NiW catalysts containing
Y zeolite and found that these catalysts were suitable for deep HDS due to their
stability and suitable pore size distribution for the diffusion and reaction of large
sulfur compounds such as alkyl substituted dibenzothiophenes.
Nakano et al. [50] investigated the effect of surface modification of USY zeolite
with alumina on the HDS and cracking activity of the Ni-Mo/Al 2 O 3 catalysts.
Various catalysts were prepared by coating of alumina over USY zeolite in different
proportions, and the performance of these catalysts was compared with physically
mixed alumina and USY zeolite-based catalysts. High HDS activity along with significant hydrocracking activity was observed using the catalyst prepared by physical
mixing of alumina and USY zeolite. In the case of alumina-coated USY zeolite
catalysts, an optimum amount of alumina coating, neither too low nor too high, was
required to obtain a better balance between HDS and hydrocracking activity.
Wang et al. [51] prepared bifunctional highly loaded NiMoW catalysts with different amounts of USY zeolites incorporated during synthesis of precursor using the
hydrothermal method and used them for the HDS of 4,6-DMDBT. HR TEM images
of the sulfided catalysts (with 0% and 10% USY zeolite in precursor) showed a
decrease in the average stacking number and average slab length in 10% USY zeolite resulting in more accessible active sites for the HDS reactions (Fig. 6). The
product distribution during hydrogenation of 4,6-DMDBT over NiMoW–USY catalysts with different wt% of USY zeolite in the precursor showed that loading of
10 wt% USY zeolite is optimal in order to obtain better HDS activity through favorable textural and morphological properties.
Han et al. [51] showed the effect of support Brønsted acidity of NiMo and
alumina- based HDS catalysts on the improved HDS and HDN activity of model
compounds through the electronic effect of the support Brønsted acid sites on the
G. Valavarasu and B. Ramachandrarao
of stacking of MoS 2 and Co-Mo-S structures. Modification of γ-Al 2 O 3 support
through incorporation of zeolites and some metal oxides was also attempted to promote the desulfurization of sterically hindered sulfur species such as alkyl DBTs
through isomerization and dealkylation. Some of these mixed oxide supports tested
for HDS applications include Al 2 O 3 -SiO 2 , Al 2 O 3 -TiO 2 , Al 2 O 3 -ZrO 2 , and Al 2 O 3 -P 2 O 5 .
Other mixed supports include Al 2 O 3 -HY and Al 2 O 3 -F.
Hydrodesulfurization of model compounds (DBT and its derivatives) and
straight-run gas oils over mixed metal oxide TiO 2 -Al 2 O 3 showed much higher activity for desulfurization compared to supported alumina-based HDT catalysts [14,
40–42]. Incorporation of Ti in the different support materials such as alumina,
SBA-15, and MCM-41 was found to show higher HDS performance for metal sulfide catalysts compared to Ti-free supports due to weak Mo-S interaction and creation of more sulfur vacancies due to reduction of Ti species to Ti3+ species under
HDS reaction conditions and subsequent transfer of spare electrons into the Mo3d
conduction band [43–47].
Fujikawa et al. [48] prepared CoMo HDS catalyst for the production of ULSD
using phosphorous and citric acid as additives on HY-Al 2 O 3 support and showed
three times higher HDS activity compared to conventional CoMoP/Al 2 O 3 catalyst
for the HDS of straight-run light gas oil feedstocks under industrial HDT conditions. Ding et al. [49] studied hydrotreating of LCO using NiW catalysts containing
Y zeolite and found that these catalysts were suitable for deep HDS due to their
stability and suitable pore size distribution for the diffusion and reaction of large
sulfur compounds such as alkyl substituted dibenzothiophenes.
Nakano et al. [50] investigated the effect of surface modification of USY zeolite
with alumina on the HDS and cracking activity of the Ni-Mo/Al 2 O 3 catalysts.
Various catalysts were prepared by coating of alumina over USY zeolite in different
proportions, and the performance of these catalysts was compared with physically
mixed alumina and USY zeolite-based catalysts. High HDS activity along with significant hydrocracking activity was observed using the catalyst prepared by physical
mixing of alumina and USY zeolite. In the case of alumina-coated USY zeolite
catalysts, an optimum amount of alumina coating, neither too low nor too high, was
required to obtain a better balance between HDS and hydrocracking activity.
Wang et al. [51] prepared bifunctional highly loaded NiMoW catalysts with different amounts of USY zeolites incorporated during synthesis of precursor using the
hydrothermal method and used them for the HDS of 4,6-DMDBT. HR TEM images
of the sulfided catalysts (with 0% and 10% USY zeolite in precursor) showed a
decrease in the average stacking number and average slab length in 10% USY zeolite resulting in more accessible active sites for the HDS reactions (Fig. 6). The
product distribution during hydrogenation of 4,6-DMDBT over NiMoW–USY catalysts with different wt% of USY zeolite in the precursor showed that loading of
10 wt% USY zeolite is optimal in order to obtain better HDS activity through favorable textural and morphological properties.
Han et al. [51] showed the effect of support Brønsted acidity of NiMo and
alumina- based HDS catalysts on the improved HDS and HDN activity of model
compounds through the electronic effect of the support Brønsted acid sites on the
G. Valavarasu and B. Ramachandrarao