On the Role of Small Amines in Zeolite Synthesis

Abstract

A systematic study explored the ability of small amines to control the zeolites obtained at the high-pH levels typical of crystallizations at SiO2/Al2O3 ratios between 20 and 40. Experiments in the absence of amine showed that mordenite (MOR) was the preferred product at the lowest ratio, and ZSM-5 was the preferred product at the highest SiO2/Al2O3 ratio. However, the addition of C2-, C3-, and C4-alkylamines changed the product dramatically. On addition of ethylamine, ZSM-5 was produced at the lowest SiO2/Al2O3 ratio, and ZSM-35 was the preferred product with C3- and C4-amines. On addition of the largest of the group, tert-butylamine, the product reverted to MOR. With polyamines such as diethylenetriamine and triethylenetetramine, ZSM-5 samples were produced having framework SiO2/Al2O3 ratios below 20. The hexane cracking activity of these samples was consistent with their exceptionally high Al content. The cyclic C4- to C6-amines, at both SiO2/Al2O3 extremes, yielded ZSM-35 and MCM-22. Again, with the l...