Controlling the Isolation and Pairing of Aluminum in Chabazite Zeolites Using Mixtures of Organic and Inorganic Structure-Directing Agents

Abstract

Synthetic methods are reported to prepare chabazite (CHA) zeolites (SSZ-13) at fixed elemental composition but with different arrangements of their framework Al atoms (Al–O(−Si–O)x–Al) between paired (x = 1, 2) and isolated (x ≥ 3) configurations. SSZ-13 zeolites (Si/Al = 15–30) that crystallized in hydroxide media and in the presence of only N,N,N-trimethyl-1-admantylammonium cations (TMAda+) contained only isolated framework Al, evident in their inability to exchange divalent Cu2+ or Co2+ cations that titrate paired Al sites. Addition of Na+ to the zeolite crystallization medium, with total cationic charge ((Na+ + TMAda+)/Al) and other synthesis parameters held constant, crystallized SSZ-13 zeolites at a fixed Si/Al ratio but with paired Al densities that increased linearly with the Na+ content incorporated into the crystalline solids. Crystallization media containing equimolar amounts of Na+ and TMAda+, but varying Al content, crystallized SSZ-13 at different compositions (Si/Al = 5, 15, 25) with the p...