Water Interaction in Faujasite Probed by in Situ X‑ray Powder Diffraction

Using in situ X-ray
diffraction and the Rietveld method combined
with the maximum entropy method, we investigated the interaction of
water with sodium faujasite and determined the sodium and water sorption
sites as a function of water content. From the information contained
in the lowest diffraction-angle peaks, we found that water also interacts
with faujasite, forming a shell-like layer inside the supercages located
at a mean distance of 2.8 Å from the pore-wall oxygens. For water-saturated
faujasite, this shell has a surface density comparable to liquid water.
The ion-exchange sites and ordered water found inside the supercage
are embedded in this layer. We included the water shell contribution
in Rietveld refinements by modeling it as a hollow sphere scatterer
inside the faujasite supercages, and the refined water and cation
quantities have agreed with nominal values.