First-principles assessment of the analogy between gas-phase and gas-solid H-abstraction reactions at graphene edges

Density functional theory (DFT) methods are used to assess the analogy between the activation energies of hydrogen abstraction reactions in gas phase and at graphene edges. We focus on prototypical hydrogen abstraction reactions by twelve C1-C5 alkyl and alkenyl radicals on both the armchair and zigzag edges of graphene. We find that the energy barriers of abstraction reactions on each edge are only determined by the stability of the abstracting radicals that are characterized by the corresponding C-H bond energy. Such correlation between the abstraction barrier and the radical stability is also shown by our calculations of the reactions in gas phase, thus revealing that the activation energies for the reactions at the gas-solid interface are linearly correlated with the ones for the reactions in the gas phase. As such, our findings provide theoretical underpinnings for the analogy between the reactions at the gas-solid interface and those in the gas phase, thus paving the way towards the estimation of the barriers of H-abstractions at the gas-solid interface of carbonaceous materials from the corresponding gas-phase reaction barriers. Such an approach is expected to play an important role in overcoming the complexity in the development of detailed microkinetic models of processes involving the interaction between gas-phase species and carbonaceous materials.