Photocatalytic oxidation on titanium dioxide
The work described in this thesis was undertaken between
October 1979 and September 1982 and is the author's own work
except where indicated by reference.
The gas phase photocatalytic oxidation of propan-2-ol to
acetone on titanium dioxide was studied.
It was found that the reaction rate varied with different
catalyst pretreatments and, in particular, it was observed
that the rate was much higher on reoxidised Ti02 than on
reduced Ti02. However, little difference was found between
the reaction rates on dehydroxylated and rehydroxylated Ti02.
These observations indicate that surface oxide ions play an
important role in the reaction, and a mechanism is proposed
which involves these ions, 2-propoxide ions, 2-propoxyl
radicals and 2-propyl hydroperoxide species.
The activation energy for the reaction on reoxidised Ti02 was
found to be in the order of 30 kJmol-1 and is thus probably
related to the release of electrons from traps lying just
below the conduction band of the semiconductor.
The reaction rate was found to be zero order with respect to
the initial pressures of propan-2-ol and oxygen, implying
that the rate determining step does not involve the
adsorption of either of these two gases. The rate was found
to be linear with illumination intensity but the quantum
yields were low (circa 5x 10-3 mol einstein-1). A kinetic
scheme is proposed to describe the above observations inwhich the rate determining step is the diffusion to the
surface and trapping of photoelectrons, and in which
significant electron-hole recombination occurs via adsorbed
Temperature programmed desorption experiments indicated that
water, propan-2-ol and acetone can all be adsorbed on Ti02 in
three different ways: (i) By hydrogen bond interactions with
surface oxide or hydroxide ions, (ii) By adsorption on
surface Ti4+ cation sites, and (iii) By dissociative
A short study was made of the photocatalytic oxidation of
propan-2-ol using Ti02 loaded with platinum deposits.
Reoxidised Pt/Ti02 was found to be extremely active and it
is suggested that the -platinum deposits both attract
electrons and act as sites for oxygen adsorption.
The photoadsorption and photocatalytic oxidation of carbon
monoxide on Ti02 was briefly investigated, and it was shown
that CO can be adsorbed as carboxylate type species and
photooxidised to carbon dioxide