Hindered Dynamic Diversity: Nuclear Magnetic Resonance Investigation of Cation Species in Zeolite Growth Systems

Traditional zeolite growth systems are notoriously difficult to study because of their complex speciation and heterogeneity. Hydrated silicate ionic liquids (HSILs) represent an attractive alternative as they are homogeneous, exhibit equilibrium speciation at all times, and can form different zeolite topologies under milder conditions. Selection of the alkali cation type and water content in HSILs offers control over the zeolitic topology. This offers a pathway to link zeolite topology to the molecular speciation and kinetics of the growth liquid as a function of cation type and concentration. Previous studies have shown that sodium and cesium present extreme cases in a series of Na‐, K‐, Rb‐ and Cs‐HSILs in terms of conductivity, viscosity, and molecular liquid structure. In this work, the local cationic environments of Na and Cs in HSILs at different concentrations are studied through an experimental–computational approach. Theoretical and experimental nuclear magnetic resonance spectroscopy combined with molecular dynamics simulations reveals a growing diversity in cation speciation and a strongly reduced mobility of species surrounding the cations when the cation concentration is increased.