Samina Azad

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Publications (3)7.39 Total impact

  • Article: Adsorption and reaction of CO and CO2 on oxidized and reduced SrTiO3(100) surfaces.
    Samina Azad, Mark H Engelhard, Li-Qiong Wang
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    ABSTRACT: The adsorption and reaction of CO and CO(2) on oxidized and reduced SrTiO(3)(100) surfaces have been studied with temperature programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). XPS results indicate that the oxidized SrTiO(3)(100) surfaces are nearly defect-free with predominantly Ti(4+) ions whereas the sputter-reduced surfaces contain substantial amounts of defects. Both CO and CO(2) are found to adsorb weakly on the oxidized SrTiO(3)(100) surfaces. On sputter-reduced surfaces, enhanced reactivity of CO and CO(2) is observed due to the presence of oxygen vacancy sites, which are responsible for dissociative adsorption of these molecules. Our studies indicate that the CO and CO(2) molecules exhibit relatively weaker interactions with SrTiO(3)(100) compared to those with TiO(2)(110) and TiO(2)(100) surfaces. This is most likely an influence of the Sr cations on the electronic structure of the Ti cations in the mixed oxide of SrTiO(3).
    The Journal of Physical Chemistry B 06/2005; 109(20):10327-31. · 3.70 Impact Factor
  • Article: Adsorption and Reaction of CO and CO2 on Oxidized and Reduced SrTiO3(100) Surfaces
    Samina Azad, Mark H. Engelhard
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    ABSTRACT: The adsorption and reaction of CO and CO2 on oxidized and reduced SrTiO3(100) surfaces have been studied with temperature programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). XPS results indicate that the oxidized SrTiO3(100) surfaces are nearly defect-free with predominantly Ti4+ ions whereas the sputter-reduced surfaces contain substantial amounts of defects. Both CO and CO2 are found to adsorb weakly on the oxidized SrTiO3(100) surfaces. On sputter-reduced surfaces, enhanced reactivity of CO and CO2 is observed due to the presence of oxygen vacancy sites, which are responsible for dissociative adsorption of these molecules. Our studies indicate that the CO and CO2 molecules exhibit relatively weaker interactions with SrTiO3(100) compared to those with TiO2(110) and TiO2(100) surfaces. This is most likely an influence of the Sr cations on the electronic structure of the Ti cations in the mixed oxide of SrTiO3.
    04/2005;
  • Article: Adsorption and reaction of methanol on stoichiometric and defective SrTiO3(100) surfaces.
    Li-Qiong Wang, Kim F Ferris, Samina Azad, Mark H Engelhard
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    ABSTRACT: The adsorption and reaction of methanol (CH(3)OH) on stoichiometric (TiO(2)-terminated) and reduced SrTiO(3)(100) surfaces have been investigated using temperature-programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), and first-principles density-functional calculations. Methanol adsorbs mostly nondissociatively on the stoichiometric SrTiO(3)(100) surface that contains predominately Ti(4+) cations. Desorption of a monolayer methanol from the stoichiometric surface is observed at approximately 250 K, whereas desorption of a multilayer methanol is found to occur at approximately 140 K. Theoretical calculations predict weak adsorption of methanol on TiO(2)-terminated SrTiO(3)(100) surfaces, in agreement with the experimental results. However, the reduced SrTiO(3)(100) surface containing Ti(3+) cations exhibits higher reactivity toward adsorbed methanol, and H(2), CH(4), and CO are the major decomposition products. The surface defects on the reduced SrTiO(3)(100) surface are partially reoxidized upon saturation exposure of CH(3)OH onto this surface at 300 K.
    The Journal of Physical Chemistry B 04/2005; 109(10):4507-13. · 3.70 Impact Factor
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