Cd2+ incorporation in small-pore LEV/ERI intergrown zeolites: A multi-methodological study

Abstract

Small-pore zeolites are successfully employed as catalysts, sorbents and molecular sieves. Their physiochemical properties can be tuned by modifying their extraframework cation (EF) composition via ion exchange. In this study, we investigate the crystal structure of a Cd-exchanged levyne ( LEV ) intergrown with erionite ( ERI ) by combining Single Crystal X-ray Diffraction (SCXRD), Molecular Dynamic simulations (MD) and Extended X-ray Absorption Fine-Structure spectroscopy (EXAFS). Data obtained from the different techniques consistently indicate that Cd 2+ in LEV is arranged in a nearly ordered fashion. In contrast, strong disorder of the EF species (Cd 2+ and H 2 O) is observed in the ERI cavities. Here, Cd 2+ forms aqueous complexes that are more mobile in comparison to LEV , where Cd 2+ bonds to both H 2 O and framework-oxygen atoms. The formation of Cd-clusters is excluded based on EXAFS analysis. Finally, to discriminate between thermal and static disorder, we propose a new approach based on combined MD and geometry optimization. • The crystal structure of Cd-LEV and Cd-ERI was determined by SCXRD. • Cd 2+ has a fairly regular octahedral coordination in Cd-LEV. • Cd 2+ is strongly disordered in the eri cavity. • Cd aqueous complexes form in Cd-ERI. • The disorder of the EF species was resolved by combining MD simulations and XAFS.