Steaming of zeolite Y: Formation of transient Al species

Steamed zeolite Y samples were examined by Al-27 MAS NMR, H-1 spin-echo editing MAS NMR, and (HAl)-H-1-Al-27} double-resonance MAS NMR in order to evaluate the dealumination process during steaming. Framework-related Al-OH groups are observed in the H-1 MAS NMR spectrum after steaming at low partial pressure (3166 Pa). These species manifest themselves in the Al-27 MAS NMR spectrum as a sharp signal due to the octahedrally coordinated species. Ammonia adsorption converts the coordination of these Al species from octahedral to tetrahedral. Steaming at high partial pressure generates a Al-27 MAS NMR spectrum that does not show the sharp line due to the octahedrally coordinated framework-related Al-OH. Therefore, the framework-related Al-OH are considered as intermediate species in the full hydrolysis of Al from the framework.