The role of alkali cations in zeolite synthesis from silicate solutions containing N,N,N-trimethyl-1-adamantammonium cations

Zeolite synthesis from aqueous N,N,N-trimethyl-1-adamantammonium (TMAA(+))-alkali (Na+, K+, Rb+, and Cs+) silicate mixtures is studied using X-ray diffraction, elemental analysis, scanning electron microscopy, and Si-29 magic angle spinning (MAS), H-1-C-13 cross-polarization (CP) MAS and H-1-Si-29 CP MAS NMR spectroscopies. SSZ-24 forms in the presence of potassium cations, and SSZ-31 crystallizes in the presence of sodium cations. This is the first report of SSZ-31 synthesis from Na-TMAA silicate mixtures. Unknown silicates form in the presence of rubidium and cesium cations, whereas no crystalline material is observed in synthesis mixtures devoid of alkali cations. The alkali cations do not appear to serve as templates or void fillers during zeolite crystallization, nor do they stabilize soluble silicate anions which serve as building blocks during zeolite crystallization. Rather, the alkali cations appear to regulate the transformation of the amorphous synthesis gel into either crystalline zeolite or other silicate phases.