LTA Zeolite Characterization Based on Pore Type Distribution

Despite the great industrial importance of zeolite LTA, there is still a gap in characterization methods, based on adsorption related to hindered diffusion of standard probe gases, such as N-2 and Ar. LTA has a three-dimensional porous structure with a high degree of symmetry; however, variations in the location of cations, notably S2 and S3 sites, lead to different energy levels in supercages. Herein, we propose to extend the pore type distribution (PTD) methodology, recently applied for metalorganic frameworks, to zeolite materials. As an application example, we selected Na-LTA (4A) zeolite. Structural properties accessed by molecular simulation methods combined with experimental adsorption isotherms of CO2 at 273 K determine the individual contribution of supercages, with different energy levels, to the total adsorption uptake. Using eight local isotherms from the supercages, we developed a kernel that estimates the most likely energy distribution levels among supercages from the best fits of experimental isotherms. The method was applied in detail for LTA samples synthesized in laboratory and supplied by an industrial manufacturer. As an extension of the approach, we also analyze the use of the average local isotherm in the determination of imperfections found in the synthesis of LTA from unconventional raw materials or its deactivation in industrial processes. The proposed methodology generates detailed and relevant information not accessed by existing methods and allows the use of adsorption to characterize this class of very small pore sieves.