The ability of quaternary ammonium polymers to influence and to direct crystallization of zeolites is described for a series of l,4-diazabicyclo[2.2.2]octane-based polyelectrolytes. Examples are shown in which polymers force crystallization of large-pore zeolites (mordenite) where small-pore species would otherwise have resulted (analcite). It is shown that polymeric cations can prevent stacking faults in a synthetic gmelinite, faults which have hitherto restricted access to the 12-ring channels of both natural and synthetic samples of this zeolite. It is proposed that these polyelectrolytes function as templates in the crystallization.
A crystallization study was undertaken to relate the structure of small amines to the zeolite product obtained.
At SiO2/Al2O3 = 200, certain noncyclic amines (some not previously recognized) were specific for the formation
of 10-ring zeolites, e.g., ZSM-22 and ZSM-23. For example, ethylmethylamine and diethylamine yielded
highly crystalline ZSM-22, while ethylamine and isopropylamine yielded ZSM-23. Consistent with their larger
size, cyclic amines such as piperazine produced the 12-ring pore system, ZSM-12. At lower SiO2/Al2O3
ratios (40), a different set of zeolites was obtained, as expected, ZSM-35 and MCM-22. Again, a specific
relationship was observed between the amine employed and the zeolite obtained. In both SiO2/Al2O3 regimes,
several amines played non-structure-specific pore- and pH-stabilizing roles and yielded ZSM-5. With relatively
few exceptions, the zeolite products were fully porefilled with amine and low in Na (Na/Al < 1). Computer
simulations confirmed a pore-stabilizing role for both structure-specific and non-structure-specific amines.
At the same time, among structure-specific (“structure-directing”) amines, they showed that the interaction
energy differences between alternative amine−pore combinations were often quite small (0.5−2.0 kcal/mol,
for example). Nevertheless, the changes in amine−pore interaction energies for this group of amines consistently
tracked the changes in zeolite products observed.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.