Cationic polymers as templates in zeolite crystallization

Abstract

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.

Synthesis of free-standing chabazite-type films

“…1(a) corresponds to the di raction pattern of the ®lm. Comparing with the data in the literature [22,23], the ®lm is mainly chabazite with traces of gmelinite intergrowths. (The three most characteristic lines (2h values) of gmelinite are 21.7°, 27.7°and 7.4°).…”

“…Chabazitegmelinite intergrowths have been reported by several researchers [22,23,26,27], indicating that these two frameworks may share similarly structured nuclei. Moreover, Daniels et al [22] observed that with increase in the Si/Al ratio of the composition, chabazite is the preferred product. For the compositions under which the chabazitetype membrane is formed (Table 1), the solutions are always more siliceous and could explain why chabazite is the primary constituent of the ®lm.…”

“…In gmelinite, the D6R units are stacked in the sequence of ABAB instead of ABCABC [23]. Chabazitegmelinite intergrowths have been reported by several researchers [22,23,26,27], indicating that these two frameworks may share similarly structured nuclei. Moreover, Daniels et al [22] observed that with increase in the Si/Al ratio of the composition, chabazite is the preferred product.…”

“…Dab-4Br has previously been utilized for a structure-directing agent for a number of zeolites including chabazite and gmelinite [6,22]. The polymers had a molecular weight estimated to be 10,000 and were synthesized according to the procedure outlined by Daniels et al [22].…”

“…Also, the composition of the ®lm as measured by powder di raction appears to be quite invariant even though the types of zeolite formed as powder at the bottom of the bottle varies. Dab4-Br is a templating agent for gmelinite [22] and in most cases, gmelinite is the primary powder product. Gmelinite is a member of the chabazite zeolite group.…”