Generalized Reaction Mechanism for the Selective Aerobic Oxidation of Aryl and Alkyl Alcohols over Nitrogen-Doped Graphene Vijaya Sundar Jeyaraj, M. Kamaraj, and V. Subramanian* Chemical Laboratory, CSIR-Central Leather Research Institute, Sardar Patel Road, Adyar, Chennai 600 020, India * S Supporting Information ABSTRACT: In this study, an attempt has been made to investigate the mechanistic pathway for the aerobic oxidation of alcohols over nitrogen-doped graphene using density functional theory methods employing a suitable model for graphene. The formation of activated oxygen species (AOS), upon oxidation, by dioxygen has been investigated with the aid of various possible nitrogen-doped models. The detailed reaction mechanism for the oxidation of benzyl alcohol and ethanol by the three AOS obtained in the present study has been unraveled. Results indicate that the ketonic oxygen species oxidizes aromatic alcohol with minimum activation energy of ∼26.5 kcal/mol. On the contrary, the activation energy for the oxidation of alkyl alcohol by AOS present at the center is the lowest, which is also similar to that of ketonic oxygen species. On the basis of the results, a generalized reaction mechanism has been arrived for alcohol oxidation by nitrogen-doped graphene. Findings reveal the valuable lead information for the optimal control over selective oxidation of alcohol by N-doped graphene based on dopant concentration and temperature 1. INTRODUCTION The selective oxidation of alcohols to aldehydes and ketones is an important industrial process. Various catalysts have been used to promote the selectivity of oxidation and the yield. 1-9 Utilization of a catalyst that is separable from the reaction mixture and exploitation of atmospheric oxygen as the ultimate oxidant is one of the attractive approaches. In this context, several experimental and theoretical studies have been performed. 10-26 Bielawski and coworkers utilized graphene oxide as a catalyst for the aerobic oxidation of alcohols to aldehydes and ketones with >90% selectivity. 27 Also, N-doped graphene has been used as a catalyst to selectively oxidize various alcohols into aldehydes and ketones in the presence of atmospheric oxygen in aqueous solutions at ambient con- ditions. Wang and coworkers have reported that N-doping of graphene enhances the aerobic oxidation of aromatic alcohols to aldehyde or ketone with >99% selectivity. 28 Watanabe et al. have used nitrogen-doped activated carbon catalyst for the oxidation of various alcohols. 29 Previous experimental and theoretical studies have provided mechanistic details and the active sites of the reaction. 28,30,31 It is found that the presence of graphitic nitrogen in the graphene lattice is responsible for the oxidation of alcohols. It is evident from previous studies that this form of nitrogen is also well-known in oxygen reduction reactions (ORR), which is catalyzed by N-doped graphene. 32-38 Graphitic nitrogen forms three σ bonds and one π bond with three nearby carbon atoms. The fifth electron belongs to nitrogen p orbital and remains as an unpaired electron and delocalized over the basal plane of graphene. Because the local domain of the graphene around the graphitic nitrogen contains an unpaired electron, it results in a net magnetic moment depending on the surface area of graphene. 39-42 This magnetic moment is capable of attracting paramagnetic molecules like dioxygen closer to the surface of graphene. This proximity provides the condition for the electron transfer from the graphene to dioxygen, resulting in the reduction of dioxygen and the formation of activated oxygen species. This property of N-doped graphene has been utilized in the oxygen reduction reaction in fuel cells. Figure 1 shows the schematic representation of electron transfer from Received: July 21, 2015 Revised: August 28, 2015 Published: September 10, 2015 Figure 1. Schematic representation of dioxygen activation by unpaired electron on N-doped graphene with the aid of pyrene as model system. Article pubs.acs.org/JPCC © 2015 American Chemical Society 26438 DOI: 10.1021/acs.jpcc.5b07070 J. Phys. Chem. C 2015, 119, 26438-26450