26
carbides, nitrides, and phosphides were also studied by many researchers for their
HDS activity, most of these studies are limited in their scope, and further extensive
research work is needed to study the catalytic performance in terms of their activity,
selectivity, and stability before utilizing them for commercial applications.
Santiago Arias et al. [87] prepared unsupported NiMoAl hydrotreating catalysts
using layered double hydrooxides (LDHs) or hydrotalcite-type materials as precursors. NiAl-terephthalate LDHs were prepared with different Al/(Al + Ni) ratios in
the range of 0.3–0.8 by ion exchange and calcination with ammonium heptamolybdate. The mixed oxides contained about 33–43 wt% Mo and Ni/Mo ratios in the
range of 0.5–1.4. Molybdenum is mostly incorporated as intercalated heptamolybdate anions (Fig. 8). Calcined mixed oxides with surface areas in the range of
26–122 m
2
/g were sulfided in situ and tested simultaneously for HDS of DBT and
hydrogenation of tetralin at a high pressure of 70 bar and temperature of 613 K in a
batch reactor. The HDS and hydrogenation activities of NiMoAl catalysts prepared
from LDHs were found to be higher than conventional NiMo/Al 2 O 3 catalysts and
similar to Al-free unsupported NiMo catalysts, but with a higher preference for
hydrogenation route.
Eijsbouts et al. [88] reviewed the technical and economic impacts of replacing
conventional promoters (Co and Ni) in HDT catalysts due to the classification of
several Ni and some soluble Co compounds as carcinogenic and toxic. Catalysts
based on noble metals are highly expensive, and other inexpensive catalyst compositions do not possess sufficient activity for ULSD and VGO FCC pretreatment
applications. Their review covered the history of conventional HDT catalysts and
alternate catalyst compositions (single transition metal sulfides, promotion with
other transition metal sulfides, Fe-based catalysts, metal carbides, metal nitrides,
Fig. 8 Fouriertransformed Ni K-edge
EXAFS spectra for the
NiAl-terephthalate LDHs
[87] (Reprinted from
Catalysis Today, 213,
Santiago Arias, Yordy
E. Licea, Luz Amparo
Palacio, Arnaldo C. Faro
Jr., Unsupported NiMoAl
hydrotreating catalysts
prepared from NiAlterephthalate hydrotalcites
exchanged with
heptamolybdate, 198–205,
2013, with permission
from Elsevier)
G. Valavarasu and B. Ramachandrarao
carbides, nitrides, and phosphides were also studied by many researchers for their
HDS activity, most of these studies are limited in their scope, and further extensive
research work is needed to study the catalytic performance in terms of their activity,
selectivity, and stability before utilizing them for commercial applications.
Santiago Arias et al. [87] prepared unsupported NiMoAl hydrotreating catalysts
using layered double hydrooxides (LDHs) or hydrotalcite-type materials as precursors. NiAl-terephthalate LDHs were prepared with different Al/(Al + Ni) ratios in
the range of 0.3–0.8 by ion exchange and calcination with ammonium heptamolybdate. The mixed oxides contained about 33–43 wt% Mo and Ni/Mo ratios in the
range of 0.5–1.4. Molybdenum is mostly incorporated as intercalated heptamolybdate anions (Fig. 8). Calcined mixed oxides with surface areas in the range of
26–122 m
2
/g were sulfided in situ and tested simultaneously for HDS of DBT and
hydrogenation of tetralin at a high pressure of 70 bar and temperature of 613 K in a
batch reactor. The HDS and hydrogenation activities of NiMoAl catalysts prepared
from LDHs were found to be higher than conventional NiMo/Al 2 O 3 catalysts and
similar to Al-free unsupported NiMo catalysts, but with a higher preference for
hydrogenation route.
Eijsbouts et al. [88] reviewed the technical and economic impacts of replacing
conventional promoters (Co and Ni) in HDT catalysts due to the classification of
several Ni and some soluble Co compounds as carcinogenic and toxic. Catalysts
based on noble metals are highly expensive, and other inexpensive catalyst compositions do not possess sufficient activity for ULSD and VGO FCC pretreatment
applications. Their review covered the history of conventional HDT catalysts and
alternate catalyst compositions (single transition metal sulfides, promotion with
other transition metal sulfides, Fe-based catalysts, metal carbides, metal nitrides,
Fig. 8 Fouriertransformed Ni K-edge
EXAFS spectra for the
NiAl-terephthalate LDHs
[87] (Reprinted from
Catalysis Today, 213,
Santiago Arias, Yordy
E. Licea, Luz Amparo
Palacio, Arnaldo C. Faro
Jr., Unsupported NiMoAl
hydrotreating catalysts
prepared from NiAlterephthalate hydrotalcites
exchanged with
heptamolybdate, 198–205,
2013, with permission
from Elsevier)
G. Valavarasu and B. Ramachandrarao