The Anomalous Adsorptive Properties of Nitric Oxide

Smith, R. Nelson; Lesnini, David; Mooi, John

doi:10.1021/j150542a011

Cited by 27 publications

(7 citation statements)

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“…Smith and co-workers2 have reported that sugar charcoal, after heating in hydrogen to reduce the surface oxides, would take up 40 times more oxygen, in the form of surface oxides, from NO than it would from air. These workers have also 3 substantiated the results of Shah. Many substances catalyse carbon oxidation reactions ; as well as affecting the rate, these catalysts generally alter the relative proportions of CO and C02 in the product. Lambert4 suggested that the function of the catalyst was to change the stability and mode of decomposition of the surface oxides.…”

supporting

confidence: 68%

The oxidation of charcoal by nitric oxide and the effect of some additives

Watts¹

1958

Trans. Faraday Soc.

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supporting

confidence: 68%

The oxidation of charcoal by nitric oxide and the effect of some additives

Watts¹

1958

Trans. Faraday Soc.

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“…where k3 is the rate constant for (R3), A3 is the Arrhenius preexponential, E3 the activation energy for (R3), [C] is the concentration of reactive sites in the carbon, and Ki is the equilibrium constant for (R2). Examining the variation of rate of C(NO) formation with temperature requires explicitly noting that d(ln K2)/d(l/T) = -AH2/R (8) such that d(ln *3)/d(l/T) = -{E3 + AH2)/R (9) Accordingly, the apparent activation energy of formation of C(NO) should be (£3 + H2). This quantity was above determined to be about 45 kJ/mol.…”

Section: Discussionmentioning

confidence: 99%

Chemisorption of nitric oxide on char. 1. Reversible nitric oxide sorption

Teng¹,

Suuberg²

1993

J. Phys. Chem.

106

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The process of chemisorption of nitric oxide (NO) on a carbon derived from phenol-formaldehyde resin has been studied at temperatures between 323 and 473 K and at N O partial pressures between 2.02 and 10.1 kPa. The process of chemisorption can be split into two separate pathways-one a reversible chemisorptive pathway forming nitric oxide surface complexes C ( N 0 ) and the other an irreversible chemisorptive pathway yielding N2 and carbon surface oxides C ( 0 ) and C(02). The enthalpy of formation of C ( N 0 ) is between 42 and 46 W/mol exothermic. The reversible pathway is governed by isotherms that are linear in NO partial pressure, within the range of pressures studied here. This same process, however, appears to be kinetically second order with respect to N O partial pressure, suggesting a possible role of NO dimer as an intermediate in the process. IatradUcti0nThe reactions of nitric oxide with carbons have been considered as offering interesting possibilities for reduction of NO emissions from combustion systems. Some of the relevant literature on these reactions has been reviewed in a paper on the global kinetics of the gasification reaction.'s2 The first step of the process, involving the chemisorption of NO on the carbon surface, has been separately con~idered.~ The literature on chemisorption and/or physisorption of NO on carbons is l i m i t~d .~-~~ Most of these studies acknowledge that if temperatures are kept low (Le., well below ambient) mainly physisorption occurs.*J0 It is generally agreed that chemisorption occurs to a significant extent at temperatures above ambient. The chemisorption is generally accompanied by formation of surface oxides and release of N2.The actual mechanism of the chemisorption processes is not yet established in any detail.One study has reported that the chemisorption of nitric oxide affects the spin-resonance absorption of charcoal in a manner similar to oxygen; there is an increase of ESR absorption linewidth with increasing extent of absorption on a cleaned carbon surface.I2 The difference is that oxygen adsorbed at room temperature can be desorbed by evacuation, whereas nitric oxide cannot. The initial absorption appears, on the basis of magnetic susceptibility, infrared, and thermal studies, to involve the addition of nitric oxide in an "N-down" config~ration.~,~ Another study casts doubt on the notion that the sites reactive toward nitric oxide addition could be spin center^.^ It also appeared that more highly heattreated carbons gave nitric oxide surface complexes of lower thermal stability.' This suggests that addition to aromatic ring structures is involved and that the number of resonance structures affects the stability of the NO adduct. In summary, it appears that the literature implies that radical addition processes occur on the surface of carbons, involving the paramagnetic nitric oxide (which is essentially free radical in nature). These addition processes appear to affect the ESR spectra but do not destroy the measurable free radicals in carbons (which ar...

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“…While chemisorption or irreversible adsorption takes places at temperatures above ambient and is followed by the formation of N 2 and surface oxides, it is physisorption or reversible adsorption that prevails at temperatures below ambient [21][22][23].…”

Section: Experimental Studies Of No Heterogeneous Reductionmentioning

confidence: 99%