Density functional study of the chemisorption of O2 on the zig-zag surface of graphite

The reaction between molecular oxygen and the zig-zag surface of two model graphites has been studied using density functional theory at the B3LYP/6-31G(d) level of theory. Chemisorption, desorption, rearrangement, and surface migration pathways were characterized and kinetic parameters computed in order to provide a mechanistic understanding of the processes occurring during carbon gasification. The chemisorption reaction is barrierless and highly exothermic, releasing 640-740kJmol−1. Surface migration reactions were found to occur with a barrier of ∼170 kJ mol−1, while two desorption processes were found to have barriers of 420 and 340 kJ mol−1, with the possibility of a stable intermediate forming in the latter pathway. Loss of CO from this stable intermediate was found to occur with a barrier of ∼170 kJ mol−1. The initial chemisorption products are highly activated due to the exothermicity of their formation and may proceed directly to CO desorption without stabilization, especially at higher temperatures. Once one molecule of CO is lost, surface migration, rearrangement, and desorption reactions of the remaining oxide were found to have barriers from 195, 470, and 400 kJ mol−1, respectively.