Thermochemical Insights into Stability and Hydration of Ion-Exchanged Zeolite ZK-5 (KFI Framework),The Journal of Physical Chemistry C

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Thermochemical Insights into Stability and Hydration of Ion-Exchanged Zeolite ZK-5 (KFI Framework)
The Journal of Physical Chemistry C ( IF 3.3 ) Pub Date : 2020-11-18 , DOI: 10.1021/acs.jpcc.0c06796
Shuhao Yang _{1,

2} , Xin Guo ₁ , Ankit Verma ₃ , Mark B. Shiflett ₃ , David R. Corbin ₃ , Alexandra Navrotsky _{1,

2}

Affiliation

Extra-framework cations not only have a great impact on the structure of zeolites but also affect energetics and absorption of guest molecules. To investigate the stability and hydration of ion-exchanged zeolite ZK-5, high-temperature oxide melt solution calorimetry and direct water absorption calorimetry were used to reveal the influence of ion exchange on formation enthalpies and hydration processes. Formation enthalpies from oxides suggest that exchanging K⁺ and Cs⁺ with protons leads to destabilization of H-ZK-5, which is accompanied by the transition to an amorphous phase at high temperature. Water absorption and corresponding enthalpies are also affected by charge-compensating cations, for example, Na⁺ ions in Na-ZK-5 promote the confinement of water molecules and generate higher water content and more exothermic absorption enthalpies. It is found that average ionic potentials are insufficient to explain formation enthalpies at different hydration levels, particularly for H-ZK-5 with complex cation forms. Instead, formation enthalpies from oxides generally become less exothermic as the distortion of the zeolite framework increases when replacing cations or absorbing/desorbing water molecules. This thermochemical study demonstrates the critical role of extra-framework cations and documents the complexity of ion exchange effects in zeolites with complicated topology and cation distribution.

中文翻译：

离子交换沸石ZK-5（KFI框架）的稳定性和水合的热化学见解

骨架外阳离子不仅对沸石的结构有很大影响，而且还会影响客体分子的能量和吸收。为了研究离子交换沸石ZK-5的稳定性和水合作用，采用高温氧化物熔融溶液量热法和直接吸水量热法揭示了离子交换对形成焓和水合过程的影响。由氧化物形成的焓表明，用质子交换K ⁺和Cs ⁺会导致H-ZK-5不稳定，并伴随着在高温下转变为非晶相。吸水阳离子和相应的焓也受电荷补偿阳离子（例如Na ⁺Na-ZK-5中的离子促进水分子的封闭并产生更高的水含量和更多的放热吸收焓。发现平均离子电势不足以解释不同水合水平下的形成焓，特别是对于具有复杂阳离子形式的H-ZK-5。取而代之的是，当更换阳离子或吸收/解吸水分子时，随着沸石骨架变形的增加，氧化物的生成焓一般不会放热。这项热化学研究证明了骨架外阳离子的关键作用，并证明了具有复杂拓扑结构和阳离子分布的沸石中离子交换作用的复杂性。

更新日期：2020-12-03

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