Abstract
In this thesis,
the selective oxidation of glycerol in the aqueous phase over
heterogeneous catalysts
is
investigated.
The work is
divided
in
to
two main parts, which
are based on
conventional
thermocatalysis and surface plasmon-assisted
photocatalysis, respectively.
In the first part, the
study focuse
s
on the use of non-precious
Copper-Cobalt-based
catalysts
for the
conventional
thermocatalytic oxidation
reaction.
The second part is devoted
to
the
exploitation of the plasmonic properties of
TiO2
supported
gold
nanoparticles
in order to assist the thermocatalytic reaction by
plasmonic photocatalysis, i.e., photon energy is used
together with thermal energy to
accelerate the reaction.
In the first part
of the thesis (Chapter 4),
the use of
copper-cobalt-based materials
for the glycerol oxidation in the aqueous phase is described.
Two different synthesis
procedures were
employed for the catalyst
preparation.
For the
first procedure, metallic
copper particles supported on ordered mesoporous cobalt monoxide were prepared
through a novel approach
by
using
a
nanocasting
method with subsequent post-treatments.
A 3D ordered mesoporous silica,
KIT-6,
was employed as
removable
template for
the
preparation of ordered mesoporous copper
cobalt oxide spinels.
A
mild reduction heat treatment with ethanol vapor was used to reduce the copper-cobalt
oxide spinel
to
form
metallic copper
nanoparticle supported on ordered mesoporous
cobalt monoxide.
As a counterpart,
non-ordered cobalt monoxide supported copper
particles were prepared by
the second procedure presented here
in, consisting of
a facile
co-precipitation method with subsequent post-treatments.
Both catalyst types were
investigated for the glycerol oxidation reaction.
Catalysts prepared by the facile co-precipitation method exhibited a superior catalytic performance with decent
recyclability compared to the corresponding mesostructured samples.
Careful
characterization of the materials before and after the reaction
provided
important
insights
into
the potentially active crystalline phases of the materials and explained the
distinguished differences
observed in the catalytic performance
between the
mesostructured and non-structured catalysts.
It was shown that the
in situ
generation of
cobalt oxyhydroxide in close contact with the formed copper oxide has
a decisive
impact on the catalytic activity.
The synergy between these two crystal phases seemed
to enhance the catalytic activity
–
whereas each phase alone
showed
strongly
diminished glycerol conversions.
Furthermore, different solvents
(apart from water)
were introduced for the oxidation reaction and it was shown that certain alcohols
as
co-solvents
have a beneficial impact on the catalytic activity of the materials.
The second part of this thesis
(Chapter 5)
is dedicated to the relatively
new field
of
plasmonic photocatalysis and
its
efficient integration into the well-studied
thermocatalytic
process
of
selective glycerol oxidation over supported gold catalysts.
The photocatalytic part of this
reaction process supports the thermocatalytic oxidation
reaction,
augmenting the
overall catalytic performance. Hence, the term
surface
plasmon-assisted glycerol oxidation
is coined in this work. Titania supported gold
catalysts with two different morphologies were investigated for the
reaction process.
It
was
shown
that a core-shell morphology with a gold core and a titania shell exhibited
no photocatalytic enhancement for the glycerol
oxidation. On the other hand, small
gold
nanoparticles deposited on
commercial
titania showed a several fold
increase
in
conversion
for reactions illuminated by visible light compared to the analogous
reactions conducted in the dark. Generally, high selectivities toward dihydroxyacetone,
a highly desired
product used in
the
cosmetic
industry, were obtained.
Moreover,
hydrogen peroxide
was identified as
a
key intermediate and essential for obtaining
improved catalytic activities with visible light irradiation.
