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Title: Photocatalytic oxidation on titanium dioxide
Author: Arnold, N. J.
Awarding Body: University of Nottingham
Current Institution: University of Nottingham
Date of Award: 1984
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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 02 species. 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 chemisorption. 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
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Chemistry, general Chemistry