Microscopic investigations of site and functional selectivity of triazole for CO2 capture and catalytic applications

Abstract

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) > C^δ+⋯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.