Kinetic study of the oxidation resistance of phosphorus-containing activated carbons

• Published in: Carbon (New York) 2012-04, Vol.50 (4), p.1523-1537
• Main Authors: Rosas, Juana María, Ruiz-Rosas, Ramiro, Rodríguez-Mirasol, José, Cordero, Tomás
• Format: Article
• Language: English
• Subjects: Activated carbon; Adsorbents; Carbon; Catalysis; Chars; Chemistry; Colloidal state and disperse state; Combustion; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Fullerenes and related materials; diamonds, graphite; Gasification; General and physical chemistry; Inhibitors; Materials science; Oxidation resistance; Phosphorus; Physics; Porous materials; Specific materials; Surface physical chemistry; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry
• ISSN: 0008-6223; 1873-3891
• DOI: 10.1016/j.carbon.2011.11.030

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–PO 3/(CO) 2PO 2 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.