Kinetics of oxygen transfer reactions on the graphene surface: Part I. NO vs. O2

Oxygen transfer reactions on carbon surfaces are of great interest for a variety of industries, as well as for the development of new technologies (e.g., NO gas detectors). They are also at the heart of the chemical surface properties and behavior of graphene-based materials. In this study we use quantum chemistry to discover the most probable ground and transition states of reactants, surface intermediates and products in the transfer of oxygen from nitric oxide and O-2 to form N-2 and CO/CO2. The graphene-NO reaction is more complex and dependent on site availability. Whereas O-2 chemisorption is barrierless, adsorption of NO is a complex function of geometric and electronic factors. Thus, the desorption of N-2 is highly favored both kinetically (from a C(NN) complex and O-down adsorption of N2O) and thermodynamically (especially via the N2O intermediate). These results are analogous to the experimental findings with a potassium catalyst. Adsorption of the NO dimer on H-saturated sites may account for the reversible chemisorption at low temperatures. These findings allowed us to propose a concise mechanism of oxygen transfer, which highlights the similarities and differences with respect to the graphene-O-2 reaction. It is also consistent with the experimentally observed concentration dependence of these reactions. (C) 2015 Elsevier Ltd. All rights reserved.