Theoretical evaluation of N-alkylcarbazoles potential in hydrogen release

• Published in: International journal of hydrogen energy 2017-04, Vol.42 (15), p.9966-9977
• Main Authors: Mehranfar, A., Izadyar, M.
• Format: Article
• Language: English
• Subjects: Dehydrogenation; Hydrogen storage; Liquid organic hydrogen carrier; N-alkylcarbazole; Reactivity indices
• ISSN: 0360-3199; 1879-3487
• DOI: 10.1016/j.ijhydene.2017.03.036

Alkyl chain effect (ethyl, propyl and butyl) on the dehydrogenation mechanism of H12-N-alkylcarbazoles has been investigated theoretically under various different conditions. Gibbs energies of activation of about 107.88 kcal mol−1 have been determined as the least energy barriers among the studied dehydrogenation processes for dehydrogenation of H12-N-ethylcarbazole to H4-N-ethylcarbazole in decalin and 57.44 kcal mol−1 for dehydrogenation of H12-N-propylcarbazole to H8-N-propylcarbazole under the experimental conditions. Kinetic and thermodynamic studies have shown that the route of H4-N-alkylcarbazoles formation passes through a higher barrier than that of the H8-N-alkylcarbazoles. Natural bond orbital (NBO) analysis showed a decrease in electron transfer between πC–C and σ*C–H at the center of the reaction. The electron density of the C–H bonds of the transition states was evaluated as evidence of hydrogen release via quantum theory of atoms in the molecules (QTAIM) procedure. Based on this analysis, a change in the nature of C–H bonds was confirmed from covalence to electrostatic interactions during the reaction. [Display omitted] •Dehydrogenation mechanism of H12-N-alkylcarbazoles was studied, theoretically.•Alkyl chain effect on the reaction rates was investigated in different conditions.•Decalin as the solvent has an important role on the energy barrier reduction.•H8-N-alkylcarbazoles as the main products are more stable than H4-N-alkylcarbazoles.