A new approach to the mechanism of heterogeneously catalysed reactions: the oxydehydrogenation of ammonia at a Cu(111) surface

Previous temperature-programmed desorption (TPD) and molecular beam studies have concluded that formaldehyde desorption is the only significant pathway in methanol oxidation at Cu(110) surfaces. We present here new TPD data for the adsorption of deuterated methanol (CD 3 OH) at a preoxidized Cu(110) surface and show that formate can be the major product of the reaction but that the experimental conditions adopted in earlier studies (specifically, preadsorption of oxygen and the adsorption of methanol at low temperatures) preclude formate formation. We propose that the reaction pathway is sensitive to the local structure of the methoxy/oxygen adlayer and suggest a model based upon this idea that reconciles the available experimental evidence. We also confirm the presence of two states of methoxy at the Cu(110)/O(a) surface and assign them to methoxy species with and without stabilization by surface oxygen.

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“…We propose that, as in the case of the NH 3 /O 2 /Cu system, 20,26 this is due to the inhibition of the growth of unreactive oxygen islands.…”

Section: Discussionmentioning

confidence: 97%

Oxidation of Methanol at Cu(110) Surfaces: New TPD Studies

Davies

Mariotti

1996

J. Phys. Chem.

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“…In all articles NH x species, in particular imide-groups, were reported to be adsorbed or formed at the copper surface what should led to resonances in the N K-edge NEXAFS spectra. Furthermore, hydroxyl groups [17], H 2 O 2 [18] or water [15,16,19,20] were the co-products from oxygen stemming either from Cu-O-rows [15,16] or "hot" transient oxygen [18][19][20]. It is pointed out that the conditions of these studies differ significantly from these used here: First, the pressure in the UHV investigations was always below 10 -6 mbar, whereas we are working in a pressure range six orders of magnitude higher.…”

Section: P Abs = 12 Mbarmentioning

confidence: 87%

“…The typical resonance for copper (I) nitride at 467.1 eV is missing which is in good agreement with the NEXAFS data at the N K-edge and the conversion data, indicating no copper (I) nitride formation and hence no deactivation. The lack of any detectable amount of nitrogen containing species on the surface is in contrast to UHV investigations of the ammonia adsorption on copper surfaces with preadsorbed oxygen [15,16] or simultaneous adsorption of a ammonia-rich NH 3 -O 2 -mixtures [17][18][19][20]. In all articles NH x species, in particular imide-groups, were reported to be adsorbed or formed at the copper surface what should led to resonances in the N K-edge NEXAFS spectra.…”

Section: P Abs = 12 Mbarmentioning

confidence: 91%

Untitled

Mayer

Hävecker²,

Knop‐Gericke³

et al. 2001

Catalysis Letters

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The oxidation of ammonia over polycrystalline copper was investigated by means of in situ NEXAFS (near edge X-ray absorption fine structure) spectroscopy in the soft X-ray ra nge. The reaction, carried out in a 1:12 excess of oxygen, was observed by mass spectrometry. The simultaneous detection of the surface electronic structure and its catalytic performance allows to correlate different reaction products to the current surfac e structure of the catalyst. It is shown that a change in total pressure from 0.4 mbar to 1.2 mbar severely affects the reaction path. Copper (I) nitride was identified as poison and a copper oxide was found to be the active phase for the selective oxidation of ammonia to nitrogen.

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“…During the period 1986-1993, the crucial role of oxygen transients in being able to control reaction pathways in oxidation catalysis was established through photoelectron spectroscopic studies of coadsorbed molecules, with evidence for the facile oxidation of water, carbon monoxide, ammonia and ethene (Carley & Roberts 1987;Boronin et al 1992;Afsin et al 1993;Carley et al 1996). The advent of STM provided crucial support for the 'fluid' nature of the chemisorbed oxygen adlayer at Cu(110) at low coverages, a feature central to the oxygen transient concept with the O K -like state being the 'active site' (Au & Roberts 1986).…”

Section: Methodsmentioning

confidence: 99%

Activation of oxygen at metal surfaces

Carley

Davies

Roberts

2005

Phil. Trans. R. Soc. A.

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Oxygen chemisorption at metal surfaces has been shown through a combination of scanning tunnelling microscopy and photoelectron spectroscopy to involve transient states that provide low energy pathways for a wide range of surface reactions including the catalytic oxidation of ammonia and hydrocarbons. The kinetically 'hot' transients are disordered and mobile, become unreactive when they form ordered structures, and are characterized by non-classical kinetic behaviour.The role of surface additives (caesium) in controlling oxygen structures and the implications of oxygen transients for theory and reaction mechanisms in applied catalysis are considered.

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A new approach to the mechanism of heterogeneously catalysed reactions: the oxydehydrogenation of ammonia at a Cu(111) surface

Cited by 44 publications

References 8 publications

Oxidation of Methanol at Cu(110) Surfaces: New TPD Studies

Oxidation of Methanol at Cu(110) Surfaces: New TPD Studies

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Activation of oxygen at metal surfaces

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