Chemistry Reference
In-Depth Information
573 K, 1.5 MPa of H
2
in a flow fixed-bed reactor.
91
During successful
HDO, there is very low coke formation on the surface of activated carbon
compared to the amount formed on a classical alumina support.
These studies show that oxide catalysts are good candidates for
hydrotreating processes.
4.4 Alternative catalysts
Besides the previously discussed catalysts, less traditional catalysts, such
as metal phosphides, are also attractive as catalysts for hydrotreating of
bio-oil.
73,90,92
A group of transition metal phosphides supported on silica were syn-
thesized and evaluated for the hydrodeoxygenation of guaiacol at 573 K
and ambient pressure.
73
The activity for HDO of guaiacol follows the
order:
Pd/Al
2
O
3
WNi
2
PWCo
2
PWFe
2
PWWPWMoPWCoMoS/Al
2
O
3
The major products for HDO of guaiacol are phenol, benzene, meth-
oxybenzene, with no catechol formed at higher contact time. At lower
contact time, catechol is the major product for Co
2
P and WP. No catechol
observed over Ni
2
P even at low contact time. The commercial 5 wt.% Pd/
Al
2
O
3
catalyst is more active than the metal phosphides at lower contact
time and the major product is catechol. The commercial hydrotreating
catalyst CoMoS/Al
2
O
3
deactivates quickly and shows little activity for the
HDO of guaiacol.
Metal nitrides and carbides were also tested in hydrotreating of bio-oil
and model compounds.
93,94
Nickel silicides have also been reported as
good catalysts for hydrogenation of phenylacetylene and cinnamaldehyde
at 0.41-3.0 MPa of H
2
pressure and 323-353 K.
95
4.5 Summary
In summary, a variety of catalysts shows good catalytic activities for
production of high quality fuels and chemicals from bio-derived feed-
stock under hydrotreating conditions. However, there are also some
disadvantages of the hydrotreating process, such as relatively high tem-
perature, high H
2
pressure, H
2
S involvement (for sulphide catalysts), and
the high price of noble metals. Furthermore, the reactants tested are
often model compounds and/or a mixture of these to simulate the
composition of bio-oil. Further studies should focus on the mechanism
and usage of real bio-oil from pyrolysis, and development of catalytic
systems, which are sulphur- and noble metal-free and which operate at
low temperature and H
2
pressure.
5 Choice of carrier material
As discussed above, the choice of support is an important aspect of the
catalyst development for the hydrotreating of bio-oil. The support influ-
ences the activity, selectivity, and the lifetime of the catalyst.
Alumina is the most commonly used support.
47,65,75,96-99
Popov et al.
determined the adsorption mode of phenol as model compound for
