A Study of the Distribution of Sodium Cations in the Zeolites NaX, NaY and ZnNaY Using Carbon Monoxide Adsorption and ²³Na NMR Techniques

Abstract

Abstract The zeolites NaX, NaY, Zn(55)NaY, and Zn(74)NaY were investigated by means of carbon monoxide adsorption and with static and magic angle spinning (MAS) 23 Na NMR spectroscopy. The Na + distribution between the sodalite (ß)- and supercages of the fully hydrated zeolites NaX and NaY were found to agree with XRD results. In the hydrated zinc-exchanged zeolites the Na + ions almost exclusively populate the ß-cages. The adsorption isotherms of CO in the dehydrated zeolites were analyzed quantitatively to yield the concentrations of Na + residing in the supercages. The measured static and MAS 23 Na NMR spectra were analyzed by comparing their widths and shapes with simulated central transition patterns and yield, inter alia, the concentrations of Na+ associated with the spectrum components. Arguments are put forward that 23Na NMR of dehydrated zeolites is well suited to distinguish Na + cations in highly symmetric environments and mobile Na + species from others located on general positions, but further resolution is hardly feasible.