The effects of seeding in the synthesis of zeolite MCM-22 in the presence of hexamethyleneimine

Zeolite crystallization proceeds much faster for MCM-22 in the presence of ''seeds,'' and crystallization times can be shortened to less than 30 h under optimal conditions. MCM-22 seems to require a very narrow range of SiO2/Al2O3 and template ratios in the reagent mixture. Under the conditions investigated, crystal development seems to progress by initially forming very thin sheets, which when isolated seem to be arranged in house-of-cards-like macrostructures. As crystallization proceeds further these sheets become thicker. Eventually the sheets coalesce, the house-of-cards structures disappear, and the crystalline mass is transformed into the denser ZSM-35 structure. (C) Elsevier Science Inc. 1997.