AVS 45th International Symposium
    Surface Science Division Thursday Sessions
       Session SS2-ThM

Paper SS2-ThM5
Photocatalytic Dehydrogenation of 2-Propanol on TiO@sub 2@(110)

Thursday, November 5, 1998, 9:40 am, Room 309

Session: Oxide Surface Chemistry
Presenter: D. Brinkley, University of Washington
Authors: D. Brinkley, University of Washington
T. Engel, University of Washington
Correspondent: Click to Email
The use of TiO@sub 2@ as a photocatalyst is not well understood at a fundamental level in environmental remediation. We have investigated the thermal and photocatalytic oxidation of small oxygen containing molecules on TiO@sub 2@ single crystal surfaces using modulated molecular beam techniques. The role of specific surface orientations, defect sites and densities, oxygen sources, surface temperature, and reaction mechanisms on the reaction probability of incident molecules are essential issues that must be understood in order to maximize the efficiency of TiO@sub 2@ as a photocatalyst. For the specific case of 2-propanol on TiO@sub 2@ (110), we found that the total probability for a thermal reaction is less than 0.03 for a single collision of an incident molecule with the surface. The major and minor products in the thermal reaction are propene and acetone respectively. The reaction probability can be increased to 0.15 in the presences of bandgap radiation and molecular oxygen on a sample which has been preannealed in vacuum to create oxygen vacancies. The increase in reactivity is due entirely to the dehydrogenation channel of the reaction. Even a fully oxidized TiO@sub 2@ (110) surface has a reaction probability of 0.08 under the same conditions. The steady state reaction yield for this system is maximized at a temperature of 350 K, with an appreciable reaction rate between 250 K and 600 K. The yield is limited by desorption of acetone below 300 K and by the decrease in the surface coverage of the reactants above 400 K. The low thermal reactivity and the significant photochemical reactivity is attributed to free radical reactions initiated through electron trapping by adsorbed molecular oxygen. Our results suggest that the reaction proceeds primarily through a mechanism in which holes are trapped by undissociated 2-propanol molecules. Studies on TiO@sub 2@ (100) are currently underway and a comparison of the reactivity of this orientation with that of the (110) surface will be presented.