Mechanistic aspects of the reaction between carbon and oxygen

Henschke, B.; Schubert, H.; Blöcker, J.; Atamny, F.; Schlögl, Robert

doi:10.1016/0040-6031(94)85135-2

Cited by 28 publications

(17 citation statements)

References 20 publications

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“…These temperatures were lower than the ones in the previous studies, [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] because the etch rate needed to be slowed on the present surface with a higher defect density. The oxidation temperature was monitored at the boat by attaching thermocouple wires.…”

Section: Methodsmentioning

confidence: 64%

Mechanistic Study of Defect-Induced Oxidation of Graphite

Hahn¹,

Kang²,

Lee³

et al. 1999

J. Phys. Chem. B

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Oxidation of a graphite initiated from surface defects is investigated by using scanning tunneling microscopy (STM) and density functional (DF) calculation. The defects are created on a graphite surface with controlled depth and density by impact of Ar + ions at low energies (50-500 eV). Oxidation of the defects with O 2 at temperatures of 450-650°C produces shallow pits on the surface via layer-by-layer etching of the carbon layer. The etch pattern and speed vary depending on the depth of a pit. Round shaped pits are produced in most cases, but less frequently anisotropic patterns are also observed for monolayer etching. A multilayer pit grows a few times faster than a monolayer pit via simultaneous etching of the top and inner carbon layers. Kinetic parameters are extracted for the oxidation of depth-differentiated pits. The activation energies are quite comparable for the oxidation of monolayer and multilayer pits, but the pre-exponential factor is larger for multilayer oxidation, which gives rise to a faster etching speed. DF calculations are performed to identify the key intermediates involved in the oxidation reactions. The calculation shows that an O 2 molecule dissociates exothermally with no energy barrier and then forms oxide species at the top or bridge sites of a carbon vacancy. A metastable O 2 * precursor state, in which an O 2 molecule adsorbs at the bridge site without dissociation, is also found. These surface species can be desorbed under the etching conditions either thermally or via further chemical reactions. Reaction pathways involving these intermediates are proposed to explain the different etching behaviors observed for mono-and multilayer pits.

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Section: Methodsmentioning

confidence: 64%

Mechanistic Study of Defect-Induced Oxidation of Graphite

Hahn¹,

Kang²,

Lee³

et al. 1999

J. Phys. Chem. B

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“…Hence, there are options to yield thermally stable, yet reactive, nanocarbons. [39,40] This is achieved by controlling the curvature and crystalline perfection of the graphene sheets either through controlled synthesis or thermal post-treatment. Using chemical etching and grafting techniques, [41] it is possible to subsequently attach a certain number and type of functional group [39,41] as a minority termination, which provide chemical reactivity for adsorbates mainly by CÀH activation.…”

Section: Active Sites and Thermal Stabilitymentioning

confidence: 99%

Metal‐Free Heterogeneous Catalysis for Sustainable Chemistry

et al. 2010

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The current established catalytic processes used in chemical industries use metals, in many cases precious metals, or metal oxides as catalysts. These are often energy-consuming and not highly selective, wasting resources and producing greenhouse gases. Metal-free heterogeneous catalysis using carbon or carbon nitride is an interesting alternative to some current industrialized chemical processes. Carbon and carbon nitride combine environmental acceptability with inexhaustible resources and allow a favorable management of energy with good thermal conductivity. Owing to lower reaction temperatures and increased selectivity, these catalysts could be candidates for green chemistry with low emission and an efficient use of the chemical feedstock. This Review highlights some recent promising activities and developments in heterogeneous catalysis using only carbon and carbon nitride as catalysts. The state-of-the-art and future challenges of metal-free heterogeneous catalysis are also discussed.

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“…From this scenario which was developed from extensive experimental observations [88,84,89,90,91,92] it is evident that efficient oxidation requires the existence of extended graphene layers for oxygen activation [90,84] and sufficient defect sites for reaction of the activated oxygen. It was found necessary in an extensive formulation of hypothetical elementary steps to invoke the existence of stationary and mobile initial oxidation products (step 4) in order to explain the varying selectivity between CO and CO 2 .…”

Section: The Reaction Of Oxygen With Carbonmentioning

confidence: 99%

“…Thermal desorption with discrimination of water and carbon oxides can be used to control the desorption of the unspecific water layer. It is observed, however, [135,88] that the water desorption affects the surface chemistry of the carbon, as some labile groups are desorbed and the vacant surface sites can react with water to form C-O-H or C-H bonds. IR spectroscopy can be used to show that even after mild desorption of water from an oxidised carbon black a variety of hydrogen species is present at the surface.…”

Section: Non-oxygen Heteroelements On Carbon Surfacesmentioning

confidence: 99%

Carbons

Schlögl

2008

Handbook of Heterogeneous Catalysis

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The element carbon plays a multiple role in heterogeneous catalysis. In homogeneous catalysis it occurs of course as the most prominent constituent of ligand systems and will be treated as such there. Carbon-containing molecules are, in most catalytic applications, the substrates of the process under consideration. Deposits and polymers of carbon often occur as poisons on catalysts. Carbon deposition is the most severe problem in certain zeolite applications. In hydrogenation reactions carbon deposits are thought to act as modifiers for the activity of the catalyst and to provide selectivity by controlling the hydrogenationdehydrogenation activity of the metal part of the catalyst. Carbon deposits are even thought to constitute part of the active sites in some cases. Carbon is a prominent catalyst support material as it allows the anchoring of metal particles on a substrate which does not exhibit solid acid-base properties. Carbon is finally a catalyst in its own right allowing the activation of oxygen and chlorine for selective oxidation, chlorination and de-chlorination reactions. These multiple roles of the element carbon are in parallel with a complex structural chemistry giving rise to families of chemically vastly different modifications of the element. It is a special characteristic of carbon chemistry that many of these modifications cannot be obtained as phase-pure materials. This limits the exact knowledge of physical and chemical properties to a few archetype modifications, namely graphite and diamond. The reason for this poor definition of materials is found in the process of its formation. This is comprised of difficult to control polymerisation reactions. Such reactions will occur also in catalytic reactions with small organic molecules. The nature of carbon deposits will therefore reflect all the complexity of the bulk carbon materials. It is one aim of this article to describe the structural and chemical complexity of "carbon" or "soot" in order to provide an understanding of the frequently observed complexity of the chemical reactivity (e.g. in re-activation processes aiming at an oxidative removal of deposits). The surface chemistry of carbon which determines its interfacial properties is a rich field as a wide variety of surface functional groups are known to exist on carbon. The by far most important family of surface functional groups are those involving oxygen. Other prominent heteroatoms on the surface are hydrogen and nitrogen. This article focusses on the description and characterisation of oxygen surface functional groups. In the final section, selected case studies of carbon chemistry in catalysis will be discussed in order to illustrate characteristic properties of carbon materials as wanted or unwanted components in catalytic systems. Regarding the literature on basic properties of carbon materials, the reader is referred to the extensive collection of review papers published in the series Chemistry and Physics of Carbon. Editors P.L.

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Mechanistic aspects of the reaction between carbon and oxygen

Cited by 28 publications

References 20 publications

Mechanistic Study of Defect-Induced Oxidation of Graphite

Mechanistic Study of Defect-Induced Oxidation of Graphite

Metal‐Free Heterogeneous Catalysis for Sustainable Chemistry

Carbons

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