Density functional study of the chemisorption of O2 across two rings of the armchair surface of graphite

The addition of molecular oxygen across two rings of the armchair surface of a model graphite 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 were computed in order to provide a mechanistic understanding of the processes occurring during carbon gasification. The initial step of the chemisorption reaction is identical to the addition across one ring of the armchair surface and has a low barrier, 18 kJ mol(-1). The barriers of subsequent steps leading to the formation of two ketone groups on separate rings are lower in energy than the initial step, and the overall reaction is 420 kJ mol(-1) exothermic. Surface migration reactions of the ketone groups were found to occur with a barrier of similar to 140 kJ mol(-1) and could form either well-separated ketone groups or a stable furan structure. Rearrangement reactions to form stable lactone and ketene species were found to have overall barriers of 104 kJ mol(-1), and these species are expected to be the major products of any molecular O-2 chemisorbing across two adjacent rings of the armchair surface. Desorption processes from these species were found to have barriers of 222 and 278 kJ mol(-1) (formation of CO) or 297 kJ mol(-1) (formation of CO2). Loss of the second CO was found to require similar to 200 kJ mol(-1), while surface migration reactions following the initial CO desorption have barriers of 131 and 206 kJ mol(-1).