Journal
CARBON
Volume 50, Issue 4, Pages 1523-1537Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.carbon.2011.11.030
Keywords
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Funding
- Ministry of Science and Innovation of Spain (DGICYT) [CTQ2009-14262]
- Junta de Andalucia [PAI-TEP184]
- Ministry of Science and Innovation of Spain
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Chemical activation of different lignocellulosic materials with phosphoric acid produces activated carbons with higher oxidation resistance than that observed for catalyst free chars obtained at similar conditions from the same biomass, even though the activated carbons have a more developed porous structure. The main reason for such behavior is probably related to the presence of thermally stable phosphorus complexes that remain on the carbon surface after the activation process. XPS analyses point out the oxidation of the phosphorus reduced groups to C-O-PO3/(CO)(2)PO2 prior to carbon gasification. The latter complexes seem to stabilize the active carbon sites. Moreover, the presence of these phosphorus inhibitors produces a change in the gasification mechanism of the activated carbons with respect to that for char. Char oxidation seems to proceed in the entire available particle surface, while activated carbon gasification is better explained by the shrinking unreacted core model. Such a difference in mechanism is attributed to the inhibition effect of the phosphorus complexes, which reduces the reactivity of carbon active sites, and could act as a physical barrier for oxygen diffusion in the micropores. (C) 2011 Elsevier Ltd. All rights reserved.
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