Surface science studies of Pd and Au on TiO2(110) single crystals

• Main Author: Sharpe, Ryan
• Published: Cardiff University 2015
• Subjects: 543; QD Chemistry
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.665896

In this thesis, the structure and reactivity of Pd, Au and Au-Pd structures on TiO2(110) single crystals has been investigated with surface science techniques, including X-ray photoelectron spectroscopy (XPS), low energy ion scattering (LEIS), Auger electron spectroscopy (AES) and temperature programmed desorption (TPD). Sputtering a clean titania single crystal resulted in reduction of the surface. The surface was partially re-oxidised by annealing in UHV and further oxidised by annealing in O2. Pd growth on TiO2(110) was found to be Volmer Weber (3D island growth) regardless of the preparation and condition of the titania – whether it was heavily sputtered, sputtered then annealed or annealed in oxygen. On annealing the Pd/TiO2(110) to temperatures above 723K, an SMSI effect was observed between the Pd nanoparticles and the TiO2 support – the Pd is encapsulated by the reduced titania support. This was found to be affected by the oxidation state of the titania – SMSI occurred at a higher temperature for an oxidised surface than for a reduced surface. Au did not show an SMSI effect and is not encapsulated by the titania support, even when annealing to temperatures of 873K. The Au film only sinters and forms nanoparticles. Pd and Au were deposited sequentially on to TiO2(110). They are proposed to form bimetallic Au-Pd core-shell structures on annealing. After continued annealing to higher temperatures an SMSI effect is once again seen. This appears to be diminished with a greater amount of Au present in the bimetallic structure. The reactivity of TiO2(110) towards several small organic molecules was studied with TPD when clean and when deposited with Pd and Au, both separately and combined. Titania showed similar reactivity to that found in the literature – ethanol decomposed primarily to ethene and acetaldehyde, formic acid gave both CO and H2O, and CO2 and H2, and acetic acid gave ketene, CO and CO2. Au was found to be unreactive. Pd was found to reduce the reactivity of the titania. Pd-Au were, in most cases, found to be more reactive than their component metals.