Thermodynamic evaluation of steam gasification mechanisms of carbonaceous materials

Reactions of water with clean, oxidized, and hydrogenated carbon surfaces were investigated using density functional theory. It was confirmed that H 2O can dissociatively chemisorb through highly exothermic reactions on the active sites of clean zigzag and armchair carbonaceous models to yield stabl...

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Bibliographic Details
Published in:Carbon (New York) 2009-11, Vol.47 (13), p.3010-3018
Main Authors: Espinal, Juan F., Mondragón, Fanor, Truong, Thanh N.
Format: Article
Language:English
Subjects:
Cross-disciplinary physics: materials science
rheology
Exact sciences and technology
Fullerenes and related materials
diamonds, graphite
Materials science
Physics
Specific materials
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Summary:Reactions of water with clean, oxidized, and hydrogenated carbon surfaces were investigated using density functional theory. It was confirmed that H 2O can dissociatively chemisorb through highly exothermic reactions on the active sites of clean zigzag and armchair carbonaceous models to yield stable intermediates such as hydroxyl, semiquinone, and cyclic ether functional groups. Since the main products of the carbon–steam gasification process are molecular hydrogen and carbon monoxide, several pathways for their evolution are proposed, all of which are endothermic reactions. The interaction of H 2O with an oxidized surface in some cases is even more exothermic than the interaction with the active sites of a clean surface. However, it becomes endothermic when H 2O interacts with a hydrogen saturated surface. Thus, the presence of hydrogen hinders the gasification reactions by blocking of the active sites rather than by removing surface oxygen.
ISSN:0008-6223
1873-3891
DOI:10.1016/j.carbon.2009.06.048