Steaming of Zeolite Y: Formation of Transient Al Species

Abstract

Steamed zeolite Y samples were examined by 27Al MAS NMR, 1H spin−echo editing MAS NMR, and 1H27Al} double-resonance MAS NMR in order to evaluate the dealumination process during steaming. Framework-related Al−OH groups are observed in the 1H MAS NMR spectrum after steaming at low partial pressure (3166 Pa). These species manifest themselves in the 27Al 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 27Al 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.