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.本研究采用原位X射线衍射（in situ X-ray diffraction）结合里特韦尔法（Rietveld method）与最大熵方法（maximum entropy method），探究了水与钠型八面沸石（sodium faujasite）的相互作用，并明确了钠与水的吸附位点随水含量的变化规律。通过分析最低衍射角处的衍射峰信息，我们发现水还可与八面沸石发生相互作用，在超笼（supercages）内部形成一层壳状结构，该结构与孔壁氧原子的平均间距为2.8 Å。对于水饱和的八面沸石，该壳层的面密度与液态水相当。超笼内部的离子交换位点与有序排布的水分子均嵌入该壳层中。我们将该水壳层建模为八面沸石超笼内的空心球散射体，并将其散射贡献纳入里特韦尔精修（Rietveld refinements）流程，最终精修得到的水与阳离子含量与理论标称值相符。