Quantum chemical studies on adsorption of CO2 on nitrogen-containing molecular segment models of coal

Abstract

The adsorption of carbon dioxide on N-containing molecular segment models of coal (2-methylpyridine, C13H9N, C23H12N, and N-doped graphenes) has been investigated by the density functional theory including dispersion correction (DFT-D3) method. Four kinds of DFT-D3 methods (BLYP-D3, PBE-D3, BP86-D3 and TPSS-D3 functionals) were used to calculate the binding energy of CO2 with 2-methylpyridine, and the results were examined by benchmark value which was calculated by the coupled-cluster calculation with singles, doubles, and perturbative triple excitations [CCSD(T)] method in the complete basis set (CBS) limit. Due to its best performance, the BLYP-D3 functional was selected to investigate the binding of CO2 to N-doped hydrocarbon clusters (C13H9N and C23H12N). The adsorption of CO2 onto several different adsorption sites and orientations on coal surface models were systematically explored. Our research indicates that increasing the size of the π-system leads to an increase in binding energy. In the C13H9N···CO2 complex, the binding energy is in the range of −2.36–−2.66kcal/mol, while C23H12N···CO2 complex has the results of −3.24–−3.56kcal/mol. We also considered the adsorption of CO2 on the periodic monolayer and bilayer N-doped graphenes. However, as no significant intermolecular charge transfer exists in the physisorption models, the effect of finite ring size on the binding energies in complexes was not obvious.