Identifying Promising Zeolite Frameworks for Separation Applications: A Building-Block-Based Approach

The concept of natural tilings provides a unique definition of the building blocks that constitute zeolite frameworks. Knowledge of the natural tiling permits the identification of different frameworks with similar structural properties. On the basis of results from earlier work, which showed a close association between energetically preferred carbon dioxide adsorption sites and certain structural building units, we propose a list of criteria to identify natural tiles that could lead to a high affinity of a zeolite framework toward CO2. After identifying all recognized framework types that incorporate tiles with these features, we perform grand-canonical Monte Carlo simulations of CO2 adsorption and CO2/N-2 mixture adsorption in these structures. Out of a set of 37 frameworks, we identify eight systems that exhibit relatively high CO2/N-2 adsorption selectivities and CO2 working capacities. An inspection of the natural filings of these systems reveals that they contain a relatively limited number of natural tiles, most of which occur in several of the eight systems. A subsequent analysis of the CO2 adsorption sites shows that identical tiles usually afford adsorption sites with very similar geometries and adsorption energies, highlighting the connection between the presence of certain tiles and the material's affinity for carbon dioxide. While the results are not directly transferable to real-world applications, this study demonstrates that an analysis of the natural tiling permits the judicious choice of candidate topologies that are particularly promising for a given task, provided that some initial information on the relationship between the structural features and the property in question is available. Similar approaches can be imagined for various applications in adsorption and catalysis.