Crystallization Model for the SUZ-4 Zeolite and Its Application in the Synthesis of Materials with an Increased Si-to-Al Ratio

The zeolite SUZ-4, with intersecting 10- and 8-member ring (MR) channels, represents an interesting topology with potential in industrial catalysis. The synthesis of SUZ-4 with a less organic template and a broader elemental composition is essential for its application in the industry. Understanding the crystallization mechanism of SUZ-4 is therefore not just of academic interest. In this study, we propose a three-stage model to categorize the crystallization period of SUZ-4 based on the evolution of ultraviolet (UV) Raman spectra: (1) the formation of 4 MR species, (2) the spatial organization of 4 MRs through the interaction with an organic template, and (3) the growth of SUZ-4 crystals. This model successfully explains the function of the tetraethylammonium hydroxide (TEAOH) template: accelerating the generation of 4 MRs, directing the formation of the nucleus, and filling the 10 MR channels in tt.tt. conformation. Based on this knowledge, precursor species at the very beginning of stage 3 were extracted and put into a further period of crystallization with replenished Si and reduced TEAOH, resulting in an increase of bulk nSi/nAl by 17% and a reduction by 72% of the original amount of the template.