Insights on the Anomalous Adsorption of Carbon Dioxide in LTA Zeolites

Abstract

We use a combination of experiments and molecular simulations to address the discrepancies of the force fields available in the literature to accurately reproduce CO2 adsorption in zeolites with high density of aluminum atoms and extra framework cations. We attribute these discrepancies to the fact that previous force fields are not parametrized to take into account the formation of carbonate-like complexes in these zeolites during CO2 adsorption. Our data show that the formation of carbonate-like complexes has a marked effect on the accessible porous structure of the zeolite, and the strength is controlled by the density and nature of extra framework cations. Strong carbonate-like complexes are formed in zeolite topologies containing high density of sodium, whereas bivalent cations give rise to more labile complexes. We provide a new set of parameters capable to reproduce the experimental adsorption in these systems. Our approach consists of the modification of the partial charges of the atoms of the zeolite that are directly involved in the formation of the surface complexes (oxygen atoms and cations). The new set of charges combined with our previous transferable force field reproduces the experimental adsorption in structures containing carbon dioxide–cation complexes.