Room-Temperature Framework Oxygen Isotope Exchange during Interaction of Water with Hydrophilic Pure-Silica Zeolites Studied Using Nuclear Magnetic resonance Spectroscopy and Neutron Diffraction

Four different hydrophobic, low-defect pure-silica zeolites are contacted with isotopically enriched water at room temperature, and all show isotope exchange of ¹⁷O into the Si-O-Si units of the zeolite structure using multiple-quantum MAS NMR spectroscopy. For the CHA zeolite structure, exchange of ¹⁸O into the framework was identified using neutron diffraction─the first time this technique has been used to differentiate oxygen isotopes in any solid-state material. The results indicate that even supposedly very hydrophobic pure-silica zeolites are susceptible to oxygen exchange under very mild aqueous conditions. This has important consequences for our view of the structure of zeolites in contact with water.