A multinuclear solid state NMR study on dealumination of mordenite by steaming and acid-leaching

The steamed and acid-leached mordenite samples were examined by high-resolution solid state H-1, Si-29, Al-17 magic angle spinning (MAS) and (HP)-H-1/Si-29 cross polarization (CP) NMR spectroscopic techniques in order to study the aluminum species and evaluate the dealumination process during steaming and leaching. The NMR experiments provide a direct evidence for the existence of nonframework four-coordinated Al species, Al(OH)(3) (.) H2O, giving rise to a H-1 resonance at delta 3.0 and a Al-27 shoulder peak at delta 45, which are different from the distorted four-coordinated Al species. At a high temperature, water molecules will favor the formation of these Al species and extra-framework penta- and hexa-coordinated Al species in the Al-27 spectrum at delta 30 and delta 0. respectively. H-1/Si-29 CP and H-1 MAS NMR showed the presence of an abundance of SiOH and AlOH groups in the dealuminated mordenites during the steaming process.