Inhibition of catalytic oxidation of carbon/carbon composites by phosphorus

Wu, Xu; Radović, Ljubiša R.

doi:10.1016/j.carbon.2005.06.038

Cited by 179 publications

(118 citation statements)

References 23 publications

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“…Most of the P, however, is assumed to be attached to the graphene zigzag edges in the form of PO 3 H 2 and OPO 3 H 2 groups, respectively. [19] The initial evolution of catalytic performances in the ODH of ethane over oCNTs and P-oCNTs is compared in Figure 2 a.…”

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confidence: 99%

Oxidative Dehydrogenation of Ethane over Multiwalled Carbon Nanotubes

et al. 2010

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The suitability of nanocarbons as catalysts for oxidative dehydrogenation (ODH) reactions has been investigated for numerous hydrocarbon substrates, such as ethylbenzene, 1-butene, isobutene, n-butane, and propane. [1][2][3][4][5][6][7][8][9] Carbon catalysts are regarded as a clean and sustainable alternative to metal oxide catalysts, [10] as their disposal after a certain lifetime by combustion is safe and environmentally benign. In addition, carbon is free of lattice or structural oxygen and can be used as a metal-free catalyst, allowing for an in-depth theoretical treatment. [1] Industrially relevant ODH product yields, however, have been achieved only for ethylbenzene due to the kinetic stabilization of the product styrene by conjugated p electrons. Hodnett described how the product yield of ODH reactions is limited by the difference in bond strengths of the weakest CÀ H bonds in the reactant and product molecules, respectively. [11] Higher differences lead to lower product yields due to consecutive combustion. On the other hand, the barrier for chemical activation of alkanes increases with decreasing chain length. [12] Thus, the oxidative activation of ethane and methane over carbon catalysts is highly challenging due to the limitation of the reaction conditions by the carbon catalyst combustion. The oxidative coupling of methane (OCM) is apparently out of reach for this catalytic system, whereas successful ethane ODH was reported over mixed metal oxides at temperatures as low as 673 K. [13] For carbon-mediated ODH catalysis, the surface oxygen groups, especially the quinoidal groups, are regarded as the active sites. [1-3, 14, 15] Oxidative stress under ODH reaction conditions, however, inevitably leads to combustion of the carbon catalyst with acidic oxygen groups as intermediates. In contrast to the ketonic groups, these groups are electrophilic and thus ultimately cause the combustion of both the alkanes and the alkenes by attack of the carbon chain. For ODH of propane, it was shown that both the combustion of the catalyst and the formation of electrophilic oxygen could be reduced by modification of carbon nanotubes with boron and phosphorus oxide. [2] Besides an empirical test of activation capability for ethane, with a high CÀH bond strength of 420.5 kJ mol À1 , this study also contains a kinetic approach to further investigate the nature of this protection effect and a thorough study of stable and unstable surface oxygen groups that might be involved in ODH catalysis.Regarding the characterization of the catalysts, temperatureprogrammed desorption (TPD) experiments of the freshly impregnated samples clearly established that the precursor salts used for B and P modification both almost completely decompose under release of H 2 O and NH 3 at below the ODH reaction temperature of 673 K (Figure 1 a). Thus, during ODH reactivity tests, the presence of the heteroatoms in the form of partially hydrated oxides can be assumed. The pronounced hygroscopic character of P 2 O 5 was nicely reflected in the lar...

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confidence: 99%

Oxidative Dehydrogenation of Ethane over Multiwalled Carbon Nanotubes

et al. 2010

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“…The introduction of chemical groups to the C-C composite aims to decrease the rate of carbon oxidation by reducing the rate of the mobility of the catalysts or by forming a barrier between the composite and oxygen [40]. Phosphorus compounds were thermally deposited by Wu and Radovic [40] by impregnating C-C composite samples using methyl-phosphoric acid (CH 3 OP(OH) 2 ) or phosphorus oxychloride (POCl 3 ) and heating at around 600°C.…”

Section: Mechanisms Of Protection Of C-c Composites Against Catalyticmentioning

confidence: 99%

“…Phosphorus compounds were thermally deposited by Wu and Radovic [40] by impregnating C-C composite samples using methyl-phosphoric acid (CH 3 OP(OH) 2 ) or phosphorus oxychloride (POCl 3 ) and heating at around 600°C. The phosphorus deposits were shown to almost completely suppress the catalytic effect of calcium, and to partially suppress that of potassium.…”

Section: Mechanisms Of Protection Of C-c Composites Against Catalyticmentioning

confidence: 99%

A review of the catalytic oxidation of carbon–carbon composite aircraft brakes

Bevilacqua

Babutskyi

Chrysanthou

2015

Carbon

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The use of de-icing chemicals at airport runways has been shown to produce oxides and carbonates of sodium, potassium and calcium which catalyse the oxidation of carbon-carbon composite aircraft brakes leading to an increase of the oxidation rate by an order of magnitude. This review reports on studies that have characterised the catalytic oxidation and discusses the mechanism of the catalytic reaction based on investigations that were carried out with both C-C composites and carbon as a fossil fuel. The alkali metal oxides/carbonates are more active catalysts and in their case, the redox reaction between the monoxides and the peroxides has been identified as the most likely catalysis mechanism. In order to reduce or eliminate the problem of catalysis, doping with boron or phosphorus compounds has been investigated by a number of researchers. The effect of these along with the use of protective coatings is also reviewed.3

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“…In the deconvolution of spectra of P 2p , there were two major peaks 40,41 : peak 1 (134.0 to 134.6 eV), metaphosphate (M[PO 3 ] n, n = 2-8, and peak 2 (133.6 to 134.7 eV), corresponding to the compounds (PhO) and 3PO (Ph indicates a phenyl group, C 6 H 5 ). In this particular case, the P atom is bonded to four O atoms by a double bond and three single bonds.…”

Section: Xps Analysismentioning

confidence: 99%