Oxygen Adsorption on Nitrogen Containing Carbon Surfaces

Introduction The reaction of O2 with carbonaceous surfaces has been widely studied due to its important application in industry. In general, O2 is first chemisorbed on an electron-rich site of the carbon basal plane of graphite and then, it dissociates into oxygen atoms. Oxygen will diffuse on the surface until finds a structural defect to form covalent bonds. If temperature is appropriated, CO can be released to the gas phase. In char and open nanotubes structures, unsaturated carbon atoms at the edge of the carbon surface can form covalent bonds with oxygen. These sites can chemisorb directly molecular oxygen to form stable carbon-oxygen complexes with a high exothermicity. Several ab initio molecular studies have been performed on the O2-carbon reaction. For instance, Kyotani et al studied the reaction of O2 to the edge of a zigzag carbon structure at the DFT//HF level and found that the O2 side-on adsorption mode is the most exothermic adsorption configuration. The same result was obtained by zhu et al in the reaction of O2 with single wall carbon nanotubes at the DFT level of theory and several carbon-oxygen complexes were found. Although studies on the O2-carbon system abound, the reaction of O2 with nitrogen containing carbonaceous surfaces is less known. The importance of nitrogen oxides in global warming and in stratospheric ozone depletion has motivated the study of NO and N2O evolution in the combustion and gasification. Therefore, our objective is to carry out oxygen adsorption on nitrogen containing carbonacesous surfaces. As a case study, we compare the thermodynamics of this reaction with the O2-carbon reaction. As a tool we employed electronic structure calculations to get insight into the nature of nitrogen-oxygen complexes.