Magic angle spinning29Si and27Al NMR study of mordenite dealumination

Magic angle spinning²⁹Si NMR presents a rapid qualitative method of assessing the degree of dealumination of sodium mordenite modified by acid leaching and heat treatment. A quantitative determination of the²⁹Si coordination sphere is hampered by the overlap of chemical shift ranges for Si?O?Al and Si?O?H species. MAS²⁷Al NMR indicates the presence of octahedrally coordinated Al in interstitial sites in all treated samples. On treating mordenite samples at high temperatures (～700°C) much of the Al becomes invisible to the NMR experiment because of its location in sites of low symmetry and large quadrupole coupling constant.