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Adsorbate Interaction

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Larry Kevan – One of the best experts on this subject based on the ideXlab platform.

  • Reducibility and Adsorbate Interactions of Ti in Titanosilicate Molecular Sieve TS-1☆
    Journal of Catalysis, 1998
    Co-Authors: A. M. Prakash, Larry Kevan
    Abstract:

    Electron spinspin resonance (ESR) and electron spin echo modulation (ESEM) spectroscopy are used to study reducibility and Adsorbate Interaction of Ti in titanosilicate TS-1 molecular sieve. Various reduction methods were used to reduce Ti(IV) in TS-1 to Ti(III) which was then monitored by ESR. When TS-1, after dehydration and oxygen treatment at high temperature followed by evacuation (activation), is γ-irradiated at 77 K; an ESR signal withg‖=1.970 andg⊥=1.906 is observed for isolated Ti(III) centers. Radiation induced defect centers known as V centers are also observed after γ-irradiation. When activated TS-1 is treated with CO or H2at 673 K, an axial ESR signal withg⊥=1.968 andg‖=1.933 is observed which is suggested to be Ti(III)(CO)nand Ti(III)(H2)ncomplexes. When activated TS-1 is exposed to D2O at room temperature and subsequently γ-irradiated at 77 K, a new ESR signal withg=1.924 is observed. This species is identified as Ti(III)-(OD)1from2D ESEM data. Adsorption of CH3OD on activated TS-1 produces a new Ti(III) species withg=1.931. This species is identified as Ti(III)-(CH3OD)1from2D ESEM data. Adsorption of C2D4on activated TS-1 produces a new Ti(III) species withg⊥=1.968 andg‖=1.910. This species is identified as Ti(III)-(C2D4)1from2D ESEM data. Possible coordination geometries of the various Ti(III)-Adsorbate complexes are discussed.

  • cuiilocation and Adsorbate Interaction in cuii exchangedsynthetic na omega gallosilicate epr and electron spin echo modulation studies
    Journal of the Chemical Society Faraday Transactions, 1997
    Co-Authors: Jeong Yeon Kim, Chul Wee Lee, Sun Jin Kim, Suk Bong Hong, Larry Kevan
    Abstract:

    The location of CuII and its Interaction with Adsorbates in CuII-exchanged synthetic Na-omega gallosilicate have been studied by EPR and electron spin echo modulation (ESEM) spectroscopies. These results are compared with those of CuII-exchanged Na-omega aluminosilicate and also those of L and offretite gallosilicates of similar channel type and size, and the differences are discussed. In general, similar results to those for CuNa-omega gallosilicate are obtained for CuNa-omega aluminosilicate. It is concluded that, in fresh hydrated omega material, CuII is in a main channel coordinating to three water molecules and to framework oxygens in the main channel wall. A minor CuII diaquo species not seen in the gallosilicate is observed in the aluminosilicate. Upon evacuation at increasing temperature, CuII moves from the main channel to a gmelinite cage. Dehydration at 410°C produces one CuII species located in a six-ring window of a gmelinite cage, based on a lack of broadening of its EPR lines by oxygen. In L and offretite gallosilicates, there is evidence for back migration of CuII from a hexagonal prism into a main channel to coordinate with Adsorbates. However, in omega the back migration from a gmelinite cage to a main channel seems to be blocked, as shown by very slow changes in the EPR spectra and differing coordination numbers for methanol, ethanol and propanol to CuII when alcohols are adsorbed. CuII does not form a complex with propanol or larger Adsorbates in omega gallosilicate. It is suggested that, in omega, small Adsorbates must diffuse into a gmelinite cage where CuII is located, to form CuII–Adsorbate complexes. The slow changes in the EPR spectra correspond to the time for Adsorbate diffusion into a gmelinite cage. CuII interacts with one molecule each of ethylene and acetonitrile, based on EPR and ESEM analyses. CuII forms a square-planar complex containing four molecules of ammonia, based on resolved nitrogen superhyperfine coupling.

  • incorporation of copper ii ions into sapo 37 cu ii ion location and Adsorbate Interaction determined by electron spin resonance and electron spin echo modulation studies
    The Journal of Physical Chemistry, 1993
    Co-Authors: Maggie Zamadics, Larry Kevan
    Abstract:

    This study focuses on Cu(II) ions incorporatcd into the silicoaluminophosphate type 37 molecular sieve. The Cu(II) species formed after equilibration with Adsorbates of differing size and polarity are studied by electron spinspin resonance and electron spin echo modulation techniques. These results are interpreted in terms of Cu(II) ion location and geometrical coordination and are compared with similar results determined for the aluminosilicate structural analog of SAPO-37, zeolite types X and Y. The adsorption of ammonia and pyridine generates a Cu(II) species which is coordinated to three Adsorbate ligands. In contrast, when various cationic forms of zeolite X and Y are exposed to the same Adsorbates, the Cu(II) cation is coordinated with four Adsorbates in a square-planar geometry

Maggie Zamadics – One of the best experts on this subject based on the ideXlab platform.

  • incorporation of copper ii ions into sapo 37 cu ii ion location and Adsorbate Interaction determined by electron spin resonance and electron spin echo modulation studies
    The Journal of Physical Chemistry, 1993
    Co-Authors: Maggie Zamadics, Larry Kevan
    Abstract:

    This study focuses on Cu(II) ions incorporatcd into the silicoaluminophosphate type 37 molecular sieve. The Cu(II) species formed after equilibration with Adsorbates of differing size and polarity are studied by electron spin resonance and electron spin echo modulation techniques. These results are interpreted in terms of Cu(II) ion location and geometrical coordination and are compared with similar results determined for the aluminosilicate structural analog of SAPO-37, zeolite types X and Y. The adsorption of ammonia and pyridine generates a Cu(II) species which is coordinated to three Adsorbate ligands. In contrast, when various cationic forms of zeolite X and Y are exposed to the same Adsorbates, the Cu(II) cation is coordinated with four Adsorbates in a square-planar geometry

  • solid state ion exchange in h sapo 34 electron spin resonance and electron spin echo modulation studies of cu ii location and Adsorbate Interaction
    The Journal of Physical Chemistry, 1992
    Co-Authors: Maggie Zamadics, Xinhua Chen, Larry Kevan
    Abstract:

    ESR and ESEM are used in this paper to study Cu(II) ion location and Interaction with water, alcohols, ammonia, and ethylene in the solid-state reactions of H-SAPO-34 with various copper compounds (CuO, CuCl{sub 2}, CuF{sub 2}). The Cu(II) ions migrate from the exterior to the interior of the molecular sieve similar to an aqueous ion exchange method. Two types of Cu(II) complexes form during the adsorption of methanol, but only one complex type forms with the rest of the Adsorbates. Cu(II) Interactions with other Adsorbate molecules are also discussed. 20 refs., 3 figs., 2 tabs.

  • study of copper ii location and Adsorbate Interaction in cuh sapo 34 molecular sieve by electron spin resonance and electron spin echo modulation spectroscopies
    The Journal of Physical Chemistry, 1992
    Co-Authors: Maggie Zamadics, Xinhua Chen, Larry Kevan
    Abstract:

    H-SAPO-34 doped with Cu(II) ions is studied by electron spinspin resonance (ESR) and electron spin echo modulation (ESEM) techniques. In the hydrated sample Cu(II) was determined to be octahedrally coordinated to three framework oxygens and three water molecules. The most likely location for this copper ion complex to reside is at a site displaced from the hexagonal window into the ellipsoidal cavity. Upon dehydration at 400 o C two distinct Cu(II) complexes are generated

Ming-chang Lin – One of the best experts on this subject based on the ideXlab platform.

  • a model study of co co Adsorbate Interaction on si 100 2 1
    Journal of Physical Chemistry B, 1999
    Co-Authors: F Bacalzogladden, Ming-chang Lin
    Abstract:

    The CO−CO Adsorbate Interaction on Si(100)-2×1 has been investigated with ab initio molecular orbital and hybrid density functional theory calculations using cluster models of the surface. Different adsorption combinations for one and two CO molecules on single- and double-dimer cluster models, Si9H12 and Si15H16, respectively, are described. Our calculations indicate that the second CO molecule is physisorbed on the same surface Si dimer where the first CO molecule is chemisorbed. The chemisorption of the first CO molecule induces a change in the charge of the surface Si dimer atoms which inhibits further Adsorbate−surface Interaction. The dissociation energy of the physisorbed second CO molecule is less than 1 kcal/mol. Adsorption of the second CO molecule on the second Si dimer is energetically preferred over coadsorption of CO on the same Si dimer. The 2OC-normal.d14 structure is the most stable configuration, with the two CO molecules adsorbed diagonally across the two Si dimers. The dissociation ene…

  • A model study of CO-CO Adsorbate Interaction on Si(100)-2×1
    The Journal of Physical Chemistry B, 1999
    Co-Authors: F. Bacalzo-gladden, Ming-chang Lin
    Abstract:

    The CO−CO Adsorbate Interaction on Si(100)-2×1 has been investigated with ab initio molecular orbital and hybrid density functional theory calculations using cluster models of the surface. Different adsorption combinations for one and two CO molecules on single- and double-dimer cluster models, Si9H12 and Si15H16, respectively, are described. Our calculations indicate that the second CO molecule is physisorbed on the same surface Si dimer where the first CO molecule is chemisorbed. The chemisorption of the first CO molecule induces a change in the charge of the surface Si dimer atoms which inhibits further Adsorbate−surface Interaction. The dissociation energy of the physisorbed second CO molecule is less than 1 kcal/mol. Adsorption of the second CO molecule on the second Si dimer is energetically preferred over coadsorption of CO on the same Si dimer. The 2OC-normal.d14 structure is the most stable configuration, with the two CO molecules adsorbed diagonally across the two Si dimers. The dissociation ene…

Jens K. Nørskov – One of the best experts on this subject based on the ideXlab platform.

  • Understanding Trends in Catalytic Activity: The Effect of AdsorbateAdsorbate Interactions for CO Oxidation Over Transition Metals
    Topics in Catalysis, 2010
    Co-Authors: Lars C. Grabow, Britt Hvolbæk, Jens K. Nørskov
    Abstract:

    Using high temperature CO oxidation as the example, trends in the reactivity of transition metals are discussed on the basis of density functional theory (DFT) calculations. Volcano type relations between the catalytic rate and adsorption energies of important intermediates are introduced and the effect of AdsorbateAdsorbate Interaction on the trends is discussed. We find that AdsorbateAdsorbate Interactions significantly increase the activity of strong binding metals (left side of the volcano) but the Interactions do not change the relative activity of different metals and have a very small influence on the position of the top of the volcano, that is, on which metal is the best catalyst.

  • Understanding Trends in Catalytic Activity: The Effect of AdsorbateAdsorbate Interactions for CO Oxidation Over Transition Metals
    Topics in Catalysis, 2010
    Co-Authors: Lars C. Grabow, Britt Hvolbæk, Jens K. Nørskov
    Abstract:

    Using high temperature CO oxidation as the example, trends in the reactivity of transition metals are discussed on the basis of density functional theory (DFT) calculations. Volcano type relations between the catalytic rate and adsorption energies of important intermediates are introduced and the effect of AdsorbateAdsorbate Interaction on the trends is discussed. We find that AdsorbateAdsorbate Interactions significantly increase the activity of strong binding metals (left side of the volcano) but the Interactions do not change the relative activity of different metals and have a very small influence on the position of the top of the volcano, that is, on which metal is the best catalyst.

N. Witkowski – One of the best experts on this subject based on the ideXlab platform.

  • When the Grafting of Double Decker Phthalocyanines on Si(100)-2 × 1 Partly Affects the Molecular Electronic Structure
    Journal of Physical Chemistry C, 2016
    Co-Authors: I. Bidermane, J. Lüder, S. Ahmadi, C. Grazioli, Marcel Bouvet, B. Brena, N. MÅrtensson, C. Puglia, N. Witkowski
    Abstract:

    A combined X-ray photoelectron specspectroscopy (XPS), scanning tunneling microscopy (STM), and density functional theory (DFT) study has been performed to characterize the Adsorbate Interaction of lutetium biphthalocyanine (LuPc2) molecules on the Si(100)-2 × 1 surface. Large molecule–substrate adsorption energies are computed and are found to compete with the molecule–molecule Interactions of the double decker molecules. A particularly good matching between STM images and computed ones confirms the deformation of the molecule upon the absorption process. The comparison between DFT calculations and XP spectra reveals that the electronic distribution in the two plateaus of the biphthalocyanine are not affected in the same manner upon the adsorption onto the silicon surface. This finding can be of particular importance in the implementation of organic molecules in hybrid devices.