| Titanium dioxide is found in a variety of industrial applications in the areas of photocatalysis, heterogeneous catalysis, gas sensing, ceramics and pigments. The understanding of the complex processes involved in these applications is facilitated by surface studies under controlled environments like UHV. A challenging surface science problem is the determination of structure-activity relationships between binding sites and reaction products. In order to study this problem, experiments were conducted on titanium dioxide in single crystal and nanoparticle form. Electron irradiation was used to create new binding sites (oxygen anionic defects) on the surfaces. Small molecules were adsorbed on all surfaces and used as reactivity probes.; The TiO2(110) single crystal surface was chosen because it is the most thermodynamically stable and it is expected to be the most abundant in nanoparticles and industrial powders. The initial experiments with a series of amines intended to characterize the acidity of the Ti4+ binding sites on the surface. The activation energies for desorption of the amines on the TiO2(110) surface were shown to correlate with the gas-phase basicities of these species, reflecting the Lewis acid character of the Ti4+ cations. Defects did not alter the adsorption behavior of the amines noticeably.; The reactivity of a series of alcohols was studied on stoichiometric and defective TiO2(110) as well. The alcohols adsorbed dissociatively, forming alkoxide and hydroxide groups. The alkoxides bound on Ti4+ sites recombined below 500 K with hydroxide groups to form the parent alcohols. When bridging oxygen defects (Ti3+) were created on the surface, the alcohols bound to these new sites and reacted above 500 K to form their corresponding alkenes (or methane, when using methanol), aldehydes and alcohols. Two different binding sites for the alkoxide species (Ti 4+ and Ti3+) were shown to be responsible for the different reaction products.; The reactivity of methanol was also studied on TiO2 nanoparticles supported on Au(111). Methanol and methane were the most abundant products observed. The nanoparticles behaved similarly to defective TiO2(110) surfaces and facetted TiO2(001) surfaces. Exposed undercoordinated Ti cations in planes other than (110) were proposed to be responsible for methane production in this case. |
