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Mo, Au and their coadsorbed layers were produced by metal vapour deposition (MVD) and thermal treatments on stoichiometric and oxygen-deficient TiO2(110) surfaces with different composition. These ultrathin metal layers were characterized by Low Energy Ion Scattering (LEIS), X-ray Photoelectron Spectroscopy (XPS), Auger Electron Spectroscopy (AES) and Scanning Tunnelling Microscopy (STM). The deposition of Mo (0.3 - 1.0 ML) at 300 K on TiO2(110) covered by 3D Au nanoparticles (above 0.5 ML)caused an increased wetting of the surface by gold. At low Au coverage (< 0.25 ML), however, the disruption of Au particles was not observed following Mo deposition, indicating that these particles bond more strongly to the reduced centers of titania than to Mo. The STM data has clearly indicated that the reversed adsorption of the two metals (Au on Mo-covered TiO2(110) surface) also results in an enhanced dispersion of gold at 300 K. It is concluded that the main driving force for the increased wetting at 300 K is the stronger bonding of Au to Mo than to either oxygen-deficient or stoichiometric TiO2 surface and the process may be activated by the kinetic energy transfered by the impinging hot metal atoms and dissipated in the supported particles. According to our LEIS measurments, the annealing of the Au(1 ML)+Mo(0.5 ML) coadsorbed layer to 900 K causes also an enhanced wetting of the oxygen deficient support by gold. During this thermal treatment, Ti remained partially in the form of Ti3+, suggesting that the oxygen-deficient sites of titania play a crucial role in the high thermal stability of gold on the surface. The complex wetting behaviour of the titania by gold in the presence of Mo was interpreted with bonding energies in the order of Au-Mo>Au-TiOx>Au-TiO2>Au-MoOy where x and y mean oxygen deficient states. Although a complete wetting of the surface by Au was not observed at 300 K or after thermal treatments in the range of 300-900 K, it can be concluded that the Mo-load leads to larger dispersity and thermal stability of Au particles offering a method for the fabrication of more effective titania supported Au catalysts. |