Cation Migration and Structural Deformations upon Dehydration of Nickel-Exchanged NaY Zeolite: A Combined Neutron Diffraction and Monte Carlo Study

Combining neutron diffraction and classical molecular simulations, we describe the cation migration and associated structural changes taking place in a Ni-exchanged NaY faujasite zeolite upon stepwise dehydration from room temperature up to 400 degrees C. The cation redistribution between sites and the related framework deformations taking place upon water removal are identified and quantified. Neutron diffraction allows monitoring the zeolite structure, the average cation location and the water content, whereas molecular modeling provides insights into the correlations between the positions of cations and water molecules. Importantly, we demonstrate that the migration of Ni2+ toward highly confined sites upon dehydration is the driving force behind deformation of the hexagonal prisms. The present work illustrates the relevance of combining these two experimental and theoretical approaches to clarify the complex interplay between cation hydration, cation location, and framework deformation. It also underlines the importance to capture the flexibility of the framework in molecular simulation of hydrated zeolite in particular when multivalent ions are involved.