Probing possible structure sensitivity in the exchange of isotopic oxygen with the surface of MgO

Mellor, Ian; Burrows, Andrew; Coluccia, Salvatore; Hargreaves, J. S. J.; Joyner, Richard W.; Kiely, Christopher J.; Martra, Gianmario; Stockenhuber, Michael; Tang, Wenyuan

doi:10.1016/j.jcat.2005.05.015

Cited by 16 publications

(10 citation statements)

References 18 publications

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“…5 In this mechanism, oxidation occurs via the transfer of lattice oxygen to the substrate, generating the oxidised product and a transient oxygen lattice vacancy within the oxide catalyst which is subsequently replenished by gas-phase oxygen containing species. This general type of mechanism, which may even be operative in non-reducible oxides, 6 has also been observed for sulfur transfer reactions involving sulfide catalysts 7 and with carbon in molybdenum carbide catalysts during methane partial oxidation. 8 To date, very limited attention has been directed towards nitrogen analogues of the Mars-van Krevelen mechanism, since nitrides are generally perceived as being inert.…”

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confidence: 53%

Towards nitrogen transfer catalysis: reactive lattice nitrogen in cobalt molybdenum nitride

et al. 2007

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confidence: 53%

Towards nitrogen transfer catalysis: reactive lattice nitrogen in cobalt molybdenum nitride

et al. 2007

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“…The ability of alkaline earth oxides such as MgO to activate oxygen and even exchange a fraction of a monolayer with the gas phase is well-known. − Since the pristine flat calcium oxide surface should not be able to activate oxygen in absence of a reducing agent or dopant, the capability of irreducible oxides to activate oxygen is often attributed to the presence of trace amounts of dopants, such as transition metals or alkali metals . In case of alkali metal dopants, the oxygen exchange could be correlated down to 0.001 atom% Na impurities in the used CaO catalyst.…”

Section: Resultsmentioning

confidence: 99%

Oxygen Activation in Oxidative Coupling of Methane on Calcium Oxide

et al. 2018

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A pulsed isotope exchange technique was applied to study the oxygen scrambling activity of polycrystalline calcium oxide under temperatures and pressures relevant for the oxidative coupling of methane (OCM). Oxygen exchange was observed above 400 °C. The onset was attributed to the removal of impurities on the catalyst surface. By trapping impurities in the gas feed, the scrambling could already be observed at room temperature. An activation energy of 80 kJ/mol was determined for the oxygen scrambling of O2 on the surface of polycrystalline CaO powder in absence of other gases. Presence of water and carbon dioxide shift the onset of the reaction to higher temperatures and increase the activation energy significantly to 110 and 150 kJ/mol, respectively. The OCM activity could be directly linked to the oxygen scrambling activity of the material in pulsed OCM operation. It is proposed that the same sites are responsible for oxygen scrambling and OCM reaction and that the rate is dictated by desorption of CO2 and H2O. The high reaction temperatures in OCM in case of CaO are only required to regenerate the active sites, which may apply to basic OCM catalysts in general. In situ Raman and thermogravimetric experiments verified the formation of a bulk calcite phase below 750 °C, which is inactive in OCM and oxygen scrambling. Above 750 °C no surface oxygen species or adsorbates were found by Raman spectroscopy suggesting that only surface defects are responsible for catalytic activity of CaO.

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“…We have shown previously that O ) ions formed via UV induced charge separation are exclusively trapped at 3-coordinated sites such as oxygen-terminated corners or kinks. A recent characterization of the related 17 O hyperfine tensor provided substantial support for this assignment [25]. In vacuum O ) radicals are stable at room temperature and represent an ideal starting point to investigate the chemical reactivity of corner sites [26,27].…”

Section: Introductionmentioning

confidence: 92%

“…Paramagnetic superoxide O À 2 and ozonide O À 3 ions have been extensively investigated by Electron Paramagnetic Resonance (EPR) spectroscopy in the past [14][15][16] and a detailed review about the chemistry and paramagnetic properties of O À 3 species is given in Ref [14]. It was found that isotopic oxygen exchange reactions on metal oxide surfaces can provide valuable insights since in some cases they correlate with catalytic activity [17]. On MgO -where a fraction of a monolayer can exchange with molecular O 2 from the gasphase -the underlying mechanism was proposed to involve ozonide radicals O À 3 generated on reaction of O 2 with surface O ) (equation 1) [17].…”

Section: Introductionmentioning

confidence: 99%

“…It was found that isotopic oxygen exchange reactions on metal oxide surfaces can provide valuable insights since in some cases they correlate with catalytic activity [17]. On MgO -where a fraction of a monolayer can exchange with molecular O 2 from the gasphase -the underlying mechanism was proposed to involve ozonide radicals O À 3 generated on reaction of O 2 with surface O ) (equation 1) [17].…”

Section: Introductionmentioning

confidence: 99%

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Ozonide ions on the surface of MgO nanocrystals

et al. 2007

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The adsorption properties of oxygen radicals on the surface of polycrystalline oxides can provide relevant information about the functionality of specific surface sites in oxidation catalysis. Using electron paramagnetic resonance spectroscopy, we investigated O 2 adsorption at MgO nanocrystal surfaces which were previously enriched with O ) radicals i.e. trapped hole centers. On dehydroxylated particle surfaces, two ozonide radical types O À 3 were isolated as adsorbates and the related energies for O 2 adsorption were found to be 55 ± 5 kJ mol )1 and 100 ± 5 kJ mol )1 . The respective adsorption sites are assigned to hole centers trapped on oxygen terminated corners and cation vancancies, respectively. In addition, O À 3 ions were also employed as probes for electron trapping sites on partially hydroxylated sample surfaces. Five types of O ) radicals emerge from surface colour centre bleaching with N 2 O, but only two of them adsorb O 2 at room temperature. A connection between the well-characterized (H + )(e -) defect -an electron trapped in close vicinity of a nearby proton [Chiesa et al. J. Phys. Chem. B 109 (2005) 7314] -and one ozonide type which exhibits significant magnetic coupling with an adjacent proton, was established on the basis of their production parameter dependence. Although the g tensor of an O 3 ) species reflects the properties of the radical itself rather than the structure of the adsorption site, the related signatures are proposed to serve also as spectroscopic fingerprints for catalytically relevant surface anion environments.

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Probing possible structure sensitivity in the exchange of isotopic oxygen with the surface of MgO

Cited by 16 publications

References 18 publications

Towards nitrogen transfer catalysis: reactive lattice nitrogen in cobalt molybdenum nitride

Towards nitrogen transfer catalysis: reactive lattice nitrogen in cobalt molybdenum nitride

Oxygen Activation in Oxidative Coupling of Methane on Calcium Oxide

Ozonide ions on the surface of MgO nanocrystals

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