Microscopic investigations of site and functional selectivity of triazole for CO2 capture and catalytic applications
Ab initio and DFT studies on CO2 interacting with different tautomers and isomers of triazole (TZ) are carried out to understand the adsorption mechanism and their mutual preferential sites. We used post Hartree–Fock methods (MP2, CCSD(T), and CCSD(T)-F12) and various DFTs (PBE, PBE0, M05-2X, and M11) with and without considering the dispersion correction for comparison. We determined hence the equilibrium structures, vibrational frequencies and binding energies of TZ–CO2 clusters and mapped their potential energy surfaces along the intermonomer coordinates. We find that the most stable TZ–CO2 clusters, some of them are already known, are not relevant for CO2 capture in porous materials. In addition, we show that the bonding between TZ and CO2 is due to various kinds of noncovalent interactions such as π-stacking, acid–base pair electron donor–electron acceptor (EDA) interactions along with N–H⋯O and C–H⋯O H-bonds with CO2. Our analysis reveals the existence of site selectivity effects when CO2 binds to TZ. These effects are related to the magnitude of the interaction potentials, in the order EDA (+N–H⋯O) > EDA (+C–H⋯O) > Cδ+⋯NN > π-stacking > σ type N–H⋯O > C–H⋯O H-bonds. This is the first report on the importance of competition between EDA, π-stacking and σ-bonds for CO2 capture and catalytic applications. Findings from this work may be used to give insights into the site specific CO2 capture ability of porous materials such as metal organic frameworks (MOFs), zeolitic imidazolate frameworks (ZIFs) or functionalized polymers. Finally, we show that IR spectroscopy of CO2 within the pores is neither a specific nor an efficient marker in probe-molecule experiments.