Oxygen transient states in catalytic oxidation at metal surfaces

Carley, Albert Frederick; Davies, Philip R.; Roberts, M. W.

doi:10.1016/j.cattod.2010.10.081

Cited by 19 publications

(12 citation statements)

References 40 publications

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“…By contrast, the adsorption of O2 is known to lead to the formation of transient electrophilic oxygen species (such as adatoms, O2 -, O -) before O 2ions are formed. 56 Although these electrophilic species are generally short-lived, they account for the formation of CO2 (and any CO) when O2…”

Section: Discussionmentioning

confidence: 99%

Elucidating the Role of CO₂ in the Soft Oxidative Dehydrogenation of Propane over Ceria-Based Catalysts

et al. 2018

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A mixed oxide support containing Ce, Zr and Al was synthesized using a physical grinding method and applied in the oxidative dehydrogenation of propane using CO2 as the oxidant. The activity of the support was compared with that of fully-formulated catalysts containing palladium. The Pd/CeZrAlOx material exhibited long-term stability and selectivity to propene (during continuous operation for 140 h) which is not normally associated with dehydrogenation catalysts. From temperature-programmed desorption of NH3 and CO2 it was found that the catalyst possessed both acidic and basic sites. In addition, temperature programmed reduction showed that palladium promoted both the reduction and re-oxidation of the support. When the role of CO2 was investigated in the absence of gas-phase oxidant, using a Temporal Analysis of Products (TAP) reactor, it was found that CO2 dissociates over the reduced catalyst leading to formation of CO and selective oxygen species. It is proposed that CO2 has the dual role of regenerating selective oxygen species, and shifting the equilibrium for alkane dehydrogenation by consuming H2 through the reverse water-gas-shift reaction. These two mechanistic functions have previously been considered to be mutually exclusive.

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Section: Discussionmentioning

confidence: 99%

Elucidating the Role of CO₂ in the Soft Oxidative Dehydrogenation of Propane over Ceria-Based Catalysts

et al. 2018

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“…The invocation of mobile, unequilibrated, hot adatoms in thermally activated reaction mechanisms on metal surfaces has precedence in the literature. [23,24] The relative amounts of molecular desorption and adatom recombination reflect the encounter rate between hot oxygen adatoms and chemisorbed dioxygen; molecular desorption is concurrent with the dissociation of dioxygen. The strong coverage dependence of the branching ratio results from changes in the local packing density of the chemisorbed dioxygen prior to dissociation at 160 K, i.e., the changing probability of a hot adatom encountering an adsorbed molecule before the atom equilibrates with the surface.…”

Section: Discussionmentioning

confidence: 99%

The dissociation-induced displacement of chemisorbed O2 by mobile O atoms and the autocatalytic recombination of O due to chain fragmentation on Ag(110)

et al. 2014

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The interplay between thermal desorption of chemisorbed dioxygen and its dissociation was studied with temperature programmed methods. Analysis of the kinetics of molecular desorption and the fraction of adsorbed molecules with dissociate is consistent with a model in which oxygen atoms released by the dissociation event induce desorption of the molecular species.These unequilibrated atoms exhibit a mean free path relative to the chemisorbed dioxygen of 1.8 nm prior to thermalization with the surface, displacing chemisorbed dioxygen within their reach. Each dissociation event leads to desorption of two oxygen molecules if the space between chemisorbed molecules approaches the minimum of 0.58 nm. This condition can be achieved experimentally by saturating the population of chemisorbed dioxygen (0.33 ML O 2 ) at 90 -100 K. Oxygen adatoms recombine near 580 K from the reconstructed (nx1)-O adlayer with kinetics dictated by progressive fragmentation of the rows. This behavior gives rise to autocatalytic recombination kinetics of oxygen adatoms which produces both an acceleration of © 2014. This manuscript version is made available under the Elsevier user license http://www.elsevier.com/open-access/userlicense/1.0/ rate at constant temperature and unusual recombination kinetics in temperature programmed desorption.

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“…, O 2 ) are highly electrophilic 14 , and can abstract hydrogen from a hydrocarbon to form alkyl radicals, which in turn will undergo consecutive oxidations to CO and CO 2 15 . Above 350 8C, the yields of decene and aromatic hydrocarbons began to rise sharply and in tandem, suggesting parallel reaction pathways.…”

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Non-lattice surface oxygen species implicated in the catalytic partial oxidation of decane to oxygenated aromatics

et al. 2012

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The one-step transformation of C(7)-C(12) linear alkanes into more valuable oxygenates provides heterogeneous catalysis with a major challenge. In evaluating the potential of a classic mixed-metal-oxide catalyst, we demonstrate new insights into the reactivity of adsorbed oxygen species. During the aerobic gas-phase conversion of n-decane over iron molybdate, the product distribution correlates with the condition of the catalyst. Selectivity to oxygenated aromatics peaks at 350 °C while the catalyst is in a fully oxidized state, whereas decene and aromatic hydrocarbons dominate at higher temperatures. The high-temperature performance is consistent with an underlying redox mechanism in which lattice oxide ions abstract hydrogen from decane. At lower temperatures, the formation of oxygenated aromatics competes with the formation of CO(2), implying that electrophilic adsorbed oxygen is involved in both reactions. We suggest, therefore, that so-called non-selective oxygen is capable of insertion into carbon-rich surface intermediates to generate aromatic partial oxidation products.

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Oxygen transient states in catalytic oxidation at metal surfaces

Cited by 19 publications

References 40 publications

Elucidating the Role of CO₂ in the Soft Oxidative Dehydrogenation of Propane over Ceria-Based Catalysts

Elucidating the Role of CO₂ in the Soft Oxidative Dehydrogenation of Propane over Ceria-Based Catalysts

The dissociation-induced displacement of chemisorbed O2 by mobile O atoms and the autocatalytic recombination of O due to chain fragmentation on Ag(110)

Non-lattice surface oxygen species implicated in the catalytic partial oxidation of decane to oxygenated aromatics

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Oxygen transient states in catalytic oxidation at metal surfaces

Cited by 19 publications

References 40 publications

Elucidating the Role of CO2 in the Soft Oxidative Dehydrogenation of Propane over Ceria-Based Catalysts

Elucidating the Role of CO2 in the Soft Oxidative Dehydrogenation of Propane over Ceria-Based Catalysts

The dissociation-induced displacement of chemisorbed O2 by mobile O atoms and the autocatalytic recombination of O due to chain fragmentation on Ag(110)

Non-lattice surface oxygen species implicated in the catalytic partial oxidation of decane to oxygenated aromatics

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Elucidating the Role of CO₂ in the Soft Oxidative Dehydrogenation of Propane over Ceria-Based Catalysts

Elucidating the Role of CO₂ in the Soft Oxidative Dehydrogenation of Propane over Ceria-Based Catalysts