Insight into Competing Reaction Mechanism of Char Oxidation by DFT Study

Abstract

This paper studied the competing oxidization mechanism of char on a zigzag carbon functionality based on the first principles by density functional theory. Studies were carried out on different oxygen chemisorption scenarios, with and without site vacancies on the edge of the char molecule, which represent an essential char oxidation at high and low temperatures, respectively. It is shown that a process of rearrangement or migration of the atom O might happen along the active carbonaceous edge before final desorptions, except for certain direct mechanisms of CO desorption by one step. CO2 can also be generated from the oxygen complex at the edge but only in an indirect way with intermediate steps. The competing characteristics were characterized and compared to produce CO and/or CO2 based on the typical reaction pathways obtained. Typically, CO proved always easier to desorb when compared to CO2 by thermal desorption from C(O). The model was essentially verified with theoretical and experimental results from the literature. Thus, the oxidation of carbon of char to yield CO and CO2 is expected to be better recovered from the view in the microscale.