Stability of van der Waals complexes of the greenhouse effect gases NH3, SO2 and CO with imidazole in gas mixtures containing CO2

Abstract

The NH, SO and CO van der Waals complexes with imidazole are characterized using highly correlated ab initio methods. The aim is to compare the behavior of greenhouse effect gases and pollutants in the presence of imidazole for predicting the ability of new materials, such as Zeolite Imidazolate Frameworks (ZIF's), for CO capture, storage and gas filters. Imidazole is considered as the simplest model to study the nature of host-guest interactions in ZIF's. Hydrogen bonding plays an important role in these polar gas capture processes, leading to three equilibrium structures of the imidazole + NH, five of the imidazole + SO, and twelve of the imidazole + CO. Real harmonic frequencies confirm the minimum energy character of these geometries. The complexation processes carry out important changes in the charge distribution of the ring. Binding energies calculated with CCSD(T)-F12 theory predict a favored adsorption of ammonia with respect to CO. In this case, the formation of intramolecular bonds involving the unprotonated nitrogen is clearly favored energetically. The binding energy corresponding to the most stable structure I1A of SO is approximately twice of the corresponding value of CO. Carbon monoxide presents the largest number of possible equilibrium structures which assure its capture by solid ZIF's although binding energies are relatively low.