Search

Abstract: The interaction of O2 with reduced rutile TiO2(110)–(1×1) has been studied by means of scanning tunneling microscopy (STM), temperature-programmed desorption (TPD) and photoelectron spectroscopy (PES). It is found that the interaction of O2 with TiO2(110) depends strongly on the reduction state of the TiO2(110) crystal. High-resolution STM studies revealed that the energy barrier for the non-vacancy-assisted, 2nd O2 dissociation channel decreases with increasing crystal reduction. Additionally, it is found in the STM studies that the Ti interstitial diffusion is slightly more facile in high-reduced TiO2(110) crystals compared to low-reduced ones. Accompanying TPD studies revealed that the line shape of the O2-TPD peak occurring between ∼360K and ∼450K depends on the crystal reduction state. For high-reduced TiO2(110) crystals characterized by large terraces most O2 molecules desorb at ∼386K, whereas O2 desorption is peaking at ∼410K for low- and medium-reduced crystals. Furthermore, the O2-TPD experiments revealed a highly non-linear behavior of the O2 desorption peak integrals as function of the crystal reduction state. The presented results point to an ionosorption model where the adsorbates withdraw the excess charge (Ti3+) from the near-surface region at temperatures<∼360K and where Ti interstitials react with oxygen species on the surface at temperatures≥∼360K. [Copyright &y& Elsevier]

The role of bulk defects in the oxygen chemistry on reduced rutile TiO2(l10) -(1 × 1) has been studied by means ot temperature programmed desorption spectroscopy and scanning tunneling microscopy measurements. Following O, adsorption at 130 K, the amount of O2 desorbing at ∼410 K initially increased with increasing density of surface oxygen vacancies but decreased after further reduction ot the TiO2(110) crystal. We explain these results by withdrawal of excess charge (Ti3+) from the TiO2(110) lattice to oxygen species on the surface and by a reaction of Ti interstitials with O adatoms upon heating. Important consequences for the understanding of the O2-TiO2 interaction are discussed. [ABSTRACT FROM AUTHOR]

Abstract: High-resolution scanning tunneling microscopy (STM) and temperature-programmed desorption (TPD) were used to study the interaction of O2 with reduced TiO2(110)–(1 × 1) crystals. STM is the technique of choice to unravel the relation between vacancy and non-vacancy assisted O2 dissociation channels as a function of temperature. It is revealed that the vacancy-assisted, first O2 dissociation channel is preferred at low temperature (~120K), whereas the non-vacancy assisted, second O2 dissociation channel operates at temperatures higher than 150K–180K. Based on the STM results on the two dissociative O2 interaction channels and the TPD data, a new comprehensive model of the O2 chemisorption on reduced TiO2(110) is proposed. The model explains the relations between the two dissociative and the molecular O2 interaction channels. The experimental data are interpreted by considering the available charge in the near-surface region of reduced TiO2(110) crystals, the kinetics of the two O2 dissociation channels as well as the kinetics of the diffusion and reaction of Ti interstitials. [Copyright &y& Elsevier]