Cooperative Structure Directing Role of the Cage-Forming Tetramethylammonium Cation and the Bulkier Benzylmethylpyrrolidinium in the Synthesis of Zeolite Ferrierite

Abstract

Hydrothermal synthesis of zeolites often requires the presence of an organic molecule or structure directing agent (SDA), which participates in the organization of the inorganic tetrahedral units into a particular topology. Bulky molecules are frequently employed as SDAs in attempts to obtain large-pore zeolite structures. However, many open-framework zeolitic structures are composed of small cages apart from the wide channels, and only small SDAs can be accommodated within these cages. These observations leaded us to design a synthesis strategy based on the combination of small molecules with bulkier cations as SDAs. The simultaneous use of tetramethylammonium (TMA) and the bulkier benzylmethylpyrrolidinium (bmp) as SDAs has led to the crystallization of the zeolite ferrierite from gels having a Si/Al ratio in the range of 16−10, in fluoride medium and in the absence of inorganic cations. Molecular mechanics calculations revealed the templating role of both cations, as the most stable configuration of the system corresponds to the siting of TMA within the FER cages, while bmp accommodates in the 10 membered-ring one-dimensional channels. Ferrierite is not obtained in the absence of either TMA or bmp, thus evidencing the co-structure directing role in the crystallization process of this zeolite.