The Effect Of Aluminum Short-Range Ordering On Carbon Dioxide Adsorption In Zeolites

The distribution of Al in cationic zeolites is important in controlling the performance of these materials, but it is challenging to measure this distribution experimentally. We examine the effect of Al ordering in a range of industrially relevant zeolites on CO2 adsorption using molecular simulations based on high quality force fields. A Reverse Monte Carlo method is used to generate Al distributions with specified degrees of order or randomness. Results for a range of Nat-exchanged zeolites show that CO2 adsorption isotherms can be used to distinguish between different degrees of Al ordering. Good agreement with experiments is observed in the limited number of cases where information is available independently about Al ordering. The differences that exist among adsorption isotherms as a function of Al ordering can be understood in terms of the existence of single- and dual-cation sites as quantified by Na-Na radial distribution functions. Our results show that measurements of CO2 adsorption combined with molecular simulations can be used to determine Al ordering in zeolites without relying on the more challenging experimental techniques previously available for this task.