BN-Doped Graphene and Single-Walled Carbon Nanotubes for the Catalysis of SN2 Reactions: Insights from Density Functional Theory Modeling.

ABSTRACT

The inner space of carbon nanotubes has already been proven to provide a type of confinement, which can dramatically alter the energetics of chemical reactions when compared to the gas phase. Moreover, BN doping can be used to fine-tune electronic properties, which might influence the enthalpy and activation energy of chemical reactions that take place inside their inner space. The energy profile of the prototype Menshutkin SN2 reaction between ammonia and chloromethane has been analyzed in a variety of carbon-based materials at the DFT (density functional theory) level. Pristine zigzag (9,0) and (12,0) single-walled carbon nanotubes and graphene sheets have been doped with boron and nitrogen at different stoichiometries, namely, BN, BNC, BNC2, and BNC4, that resulted in remarkable variations of their catalytic effects. Graphene has revealed to be the support material, which depends less on doping in terms of enthalpy and energy barrier of the reaction. However, when graphene is rolled up into tubular forms, the influence of doping becomes increasingly stronger as the nanotube radius decreases. In the case of BNC4 doping of (9,0) nanotubes, the activation energy drops 10 kcal/mol when compared to the pristine case, and the reaction became even exothermic by more than 15 kcal/mol.