A comparison of O2 and CO2 oxidation of glassy carbon surfaces

doi:10.1016/0008-6223(85)90234-9

Carbon

Volume 23, Issue 6, 1985, Pages 723-729

https://doi.org/10.1016/0008-6223(85)90234-9 Get rights and content

Abstract

We have separated and studied with surface spectroscopies the dissociative adsorption step from the CO formation step in the O₂ and CO₂ gasification of glassy carbon. The reactive adsorption probabilities decreased with increased coverage. Differences between O₂ and CO₂ were apparent at high oxygen coverages where the dissociative adsorption probability at 300°C for CO₂ drops below 10⁻¹⁴, which is orders of magnitude less than that of O₂. Estimates for the activation energy for dissociative adsorption at high coverage are 32 kcal/mol for O₂ and 50–60 kcal/mol for CO₂. We have examined the thermal stabilities of the resultant oxidized surfaces that yield desorption energies and provide quantitative information about the product formation step in gasification reactions. A substantial fraction of the oxygen on the carbon surface is very stable with CO formation energies of >80 kcal/mol. The energies decrease as a function of increasing oxygen coverage and at high coverages decrease below 70 kcal/mol. The energetics of CO formation from lattice carbon limit the rate of gasification by CO₂. The increased gasification activity for O₂ is associated with a more facile gaseous dissociation step causing higher oxygen coverages, which in turn generates lower energy CO formation sites.

References (24)

P.L. Walker et al.
Adv. Catalysis
(1959)
N.M. Laurendeau
Prog. Energy Combust. Sci.
(1978)
J.B. Donnet
Carbon
(1982)
L.R. Radovic et al.
Fuel
(1983)
S.B. Tong et al.
Carbon
(1982)
P.J. Hart et al.
Carbon
(1967)
R.C. Bansal et al.
J. Colloid Interface Sci.
(1970)
M. Barber et al.
Chem. Phys. Lett.
(1973)
S.R. Kelemen et al.
Surface Sci.
(1984)
R.O. Lussow et al.
Carbon
(1967)

P.L. Walker et al.

Fundamentals of Gas Surface Interactions

R. Schlogl et al.

Carbon

(1983)

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A comparison of O2 and CO2 oxidation of glassy carbon surfaces

Abstract

Adv. Catalysis

Prog. Energy Combust. Sci.

Carbon

Fuel

Carbon

Carbon

J. Colloid Interface Sci.

Chem. Phys. Lett.

Surface Sci.

Carbon

Carbon

A comparison of O₂ and CO₂ oxidation of glassy carbon surfaces