Impact of the Zn source on the RSN-type zeolite formation

Abstract

A typical zeolite synthesis reaction mixture involves a framework atom source, a solvent, a mineraliser, and a structure directing agent. However, these components often have a dual function, and their impact on the nucleation/crystallization process is difficult to establish straightforwardly. The present study deals with the structure directing effect of zinc on the preparation of zincosilicate RUB-17 (RSN-type material). First, an attempt was made to introduce several other heteroatoms (Al, B, Ge, Mg, Li, and Zr) into the RSN framework under the same reaction conditions as those for Zn-RSN. Second, different Zn sources have been employed in order to study their impact on RUB-17 intermediates and the final product properties. The obtained series of samples were analysed by XRD, XRF, GISAXS, SEM, TEM, and TG as well as by Raman, NMR, infrared and solid state UV/VIS spectroscopy. The physicochemical analysis of the obtained solids was complemented by DFT modelling. The results show that a RSN-type material can be solely prepared in the Zn-containing systems, where zinc plays a structure directing role besides its function as a framework cation. Namely, the lov-unit, a basic building unit of the RSN framework, is formed at the very beginning of the crystallization no matter the zinc source employed. Yet, the differences in the crystallization of different systems and relatively long time needed for full transformation of the precursor indicate that there is some other limiting step that accounts for the formation of zeolites.