Seeding on the Synthesis of MCM-22 (MWW) Zeolite by Dry-Gel Conversion Method and its Catalytic Properties on the Skeleton Isomerization and the Cracking of Hexane

Abstract

The effects of seeding on synthesis of MCM-22 (MWW) have been studied by the dry gel conversion (DGC) method. Highly reproducible crystalline MWW zeolite could be obtained by DGC method, using seeds of calcined sodium MWW with SiO₂/Al₂O₃=31. Crystallization of MWW phase was completed in the presence of seeds (2 mass% against SiO₂) at 150°C within two days. The small amount of seed (0.25 mass% against SiO₂) was sufficient for the required phase formation of MWW. The MWW with SiO₂/Al₂O₃ ratio from 35 to 66 was obtained as pure phase; however, the crystallinity of MWW decreased with further increase in the ratio: products were contaminated with impurities.
The catalytic properties of MWW were examined in the skeleton isomerization and the cracking of hexane, and compared to zeolites such as BEA, MFI, and MOR. The catalytic activities were in the order: MFI>BEA>MWW>>MOR; however, the selectivity for the isomerization were in the order: BEA>MWW>MFI. These catalytic properties were due to the differences of structures and acid strength of zeolites.