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.