Effect of aluminum on the formation of zeolite MCM-22 and kenyaite

The synthesis of zeolite MCM-22 and kenyaite under static hydrothermal conditions using hexamethyleneimide (HMI) as a directing agent was investigated. Kenyaite was the favored product instead of the purr silica analogue of MCM-22 for a pure silica synthesis mixture. With increasing SiO2/Al2O3 ratio, the crystallized products varied from purr MCM-22 to a mixture of MCM-22 and kenyaite, and finally pure layered silicate kenyaite. The fraction of MCM22 crystallites increases, whilst that of kenyaite decreases with the aluminum content. All the products occlude HMI molecules, and the amount of HMI increases with the aluminum content. MCM-22 and kenyaite have different layer structures, but the Si atoms in the HMI-included kenyaite have similar NMR chemical shifts as those in MCM-22. Aluminum atoms, which are present as tetrahedral framework species, are most possibly incorporated into the framework of MCM-22 only. The presence of aluminum seems to be critical for the formation of MCM-22 zeolite. (C) 2001 Elsevier Science B.V. All rights reserved.