Chemistry Reference
In-Depth Information
bio-oil during hydrotreating over a sulfided CoMo catalyst supported on
alumina by infrared spectroscopy.
97
Phenol dissociates on the support
but did not strongly interact with the sulfide phase when saturating
the catalyst at 400 1C in a phenol/argon flow. After phenol adsorption, the
accessibility of support sites is decreased. Moreover, a decrease of the
accessibility of the sulfide sites is also observed. Apparently, there is an
indirect poisoning of the sulfide edge sites by phenolate species an-
chored on the support and close to the sulfide slabs. The decrease of the
amount and/or strength of the acid-base pairs of the alumina support
could be a way to limit deactivation by phenol. Using more complex
phenolic compounds such as guaiacol, lead to similar conclusions.
99
This study is one of the first steps in the rational design of more ecient
and stable hydrotreating catalysts of bio-oil.
Others have reported that alumina may not be a suitable support,
because of the presence of water in the reaction mixture, which may
induce the conversion of alumina into boehmite under the reaction
conditions.
47,98
Laurent and Delmon determined the influence of water
on the activity of sulfide NiMo/g-alumina during hydrodeoxygenation of
4-methylphenol.
98
The water causes the activity of a sulfide nickel-
molybdenum catalyst to decrease by two-third in less than 60 h. The
reason is the partial conversion of g-alumina into hydrated boehmite.
The conversion is permanent in the sense that the activity is not restored
in the presence of hydrogen sulfide and after removal of water. Fur-
thermore, the water causes a partial oxidation of the nickel sulfide into
oxidized nickel species, which are not as active as sulfided nickel species.
Carbon has been suggested as a better support for the hydrotreating
catalysts.
13,45,73,91,100-102
This type of support has low acidity, high por-
osity, and high surface area. A study of Echeandia et al. shows that the
neutral nature of carbon was advantageous, as this gave a lower tendency
for coke formation compared to other supports like alumina.
91
This will
prolong the lifetime of the catalysts.
Silica and silica-alumina are frequently-used supports for hydrotreat-
ing catalysts.
73,99
A comparison of adsorption of phenolic model com-
pounds on silica and alumina shows that the strong interaction between
the phenolic compounds and the alumina support could be a source for
catalyst deactivation (vide supra). Silica aluminas are a good alternative
provided that a high dispersion of the active phase can be achieved,
suggesting that silica-based supports should be considered as potential
candidates to design HDO catalyst with better stability.
99
Other oxides like cerium, titanium, and zirconium oxides have also
been tested and the effect of these supports during hydrotreating pro-
cesses is reported (as shown in Fig. 9).
77,96,100
For supported cobalt-
molybdenum sulphide catalysts during HDO of model compound
guaiacol, zirconium oxide as support shows very high catalytic activity
compared to CoMoS supported on g-alumina or titanium oxide.
96
Fur-
thermore, CoMoS/ZrO
2
is especially selective towards C
aromatic
-O hydro-
genolysis under the HDO conditions. Methylation reactions which occur
with the alumina support and the formation of heavier products, pre-
cursors of coke, reduce the catalytic activity towards deoxygenated
