Abstract
Inspired by the concept
that hydrophobic
surface
properties
could improve the stability of
HDO catalysts,
in this thesis the effect of catalyst
surface
polarity and stability was
systematically investigated. In
Chapter 3
the influence of catalyst polarity was studied
systematically
using
Ni2P/SiO2
catalysts as a models
which deactivated by oxidation
through water. For this purpose,
a series of organically modified Ni2P/SiO2
catalysts was
prepared,
modifying a known sol-gel synthesis.
Notably,
it was found that there is
a
threshold in terms of hydrophobicity, which has to be reached to stabilize the catalyst
against
oxidation. Moreover, the modification did also influence the reactivity of the
catalysts in HDO reactions. Interestingly,
catalysts modified with alkane groups did
display a lower reactivity, compared to unmodified catalysts or catalysts modified with
benzyl groups.
Probably,
this is caused by the low polarity of alkane groups, compared to
OH groups present on unmodified silica or benzyl modified silica, resulting in a decreased
affinity of the relatively polar bio-oil model compounds towards the catalyst.
In Chapter 4,
a different
approach for the synthesis of hydrophobic Ni2P/SiO2
catalysts
was introduced. In this approach,
the dual role of TOP in the synthesis of Ni2P,
starting
with
a commercial Ni/SiO2
catalyst,
was elucidated. The dual role of
TOP in this system
consists of being the P-source
for the conversion of
the metallic Ni precursor into
Ni2P,
and by
conferring
a hydrophobic character to the catalyst due to the
adsorption of excess
TOP groups on the catalyst surface. Hence the catalyst with TOP groups on the catalyst
could be recycled for 6 times without deactivating. These results are in good agreement
with the above mentioned literature reports, as well as the
results presented in
Chapter 3.
Finally, in
Chapter 5 ̧
the catalyst introduced in
Chapter 4
was applied to real lignin
bio-oil feedstocks obtained by
a
catalytic
upstream
biorefining process. The
optimal
reaction conditions described Chapter 4
for a model compound,
could successfully
be
translated into those employed for the conversion of
real feedstock. Therefore,
either
aromatic or aliphatic product mixtures were
effectively
obtained by applying suitable
reaction conditions.
Moreover, a new process design was introduced, in collaboration with
Dr. Zhenwen Cao, suggesting that steam reforming of the hollocellulose pulp, which is the
second product of the catalytic
biorefining process, could supply the required hydrogen
for the hydrotreatment of the lignin bio-oil.
In conclusion,
this thesis further
substantiates
the idea that
hydrophobization of HDO
catalysts is a suitable method
for
stabilizing HDO catalysts,
which
are sensitive
to
oxidation
by water.
This concept could also be used for other catalyst systems, which are
less sensitive to water, to improve their long-term stability during hydrotreament
of real
bio-oil feedstocks and,
therefore,
make this process more
feasible
for economic purposes.
