Stability of Van der Waals complexes of the greenhouse effect gases CH4and SF6with imidazole in gas mixtures containing CO2

Electronic structure calculations are applied to the study of the properties of the Zeolite Imidazolate Frameworks (ZIFs) for gas capture of the greenhouse effect gases CO2, CH4and SF6. Van-der-Walls complexes of these adsorbates with imidazole are explored considering the imidazolate rings simplest models for the study of the nature of host-guest interactions in ZIFs. The minimum energy paths for complexation are described by determining global interaction potential energy surfaces. The approach of SF6to the imidazole can produce its decomposition due to heterogeneous catalysis. The number of the complex stable geometries, depending on the size and polarity of the adsorbate, makes more probable its adsorption. The calculations prove that capture by imidazoles is energetically favored for the three adsorbates, CO2displays the largest ability for binding imidazolate rings and methane presents the larger number of structures. CH4and SF6can be expected to be strong competitors while the molecular size of SF6can yield to important steric effects. The stability of three body complexes type CH4-imidazole-CO2and SF6-imidazole-CO2confirms the probability of simultaneous attachments.