Layering of ferrierite sheets by using large co-structure directing agents: Zeolite synthesis using 1-benzyl-1-methylpyrrolidinium and tetraethylammonium

In view of the success of our new synthesis methodology regarding the use of co-structure directing agents (co-SDA) in zeolite synthesis, and in a search for the discovery of new stable ferrierite-type layered materials, which are useful precursors for the productions of shape-selective catalysts, we have further explored the use of co-SDAs by using a new cation, tetraethylammonium (TEA), as co-SDA together with the larger 1-benzyl-1-methylpyrrolidinium cation (bmp). As a result, layered ferrierite-type materials with a large interlayer separation have been obtained. Interestingly, in contrast to the ferrierite layered materials obtained with quinuclidine and bmp using the same approach, these layered materials are stable in time, i.e., an increase of the crystallisation time does not lead in this case to an approach of the layers to finally yield a more condensed ferrierite (FER) structure, as was the case for the materials obtained with quinuclidine. A complementary computational study allowed us to gain insights into the mechanism of crystallisation of ferrierite-type materials in this system. Simulation results evidenced that the inability of TEA to direct the synthesis of the fully-condensed structure is due to the large size of the TEA cations that can be accommodated neither in the cavities nor in the 10 MR channels of the fully-condensed FER structure. Instead, the simulations show that the most stable situation for the accommodation of this co-SDA in the ferrierite cavities is reached when the FER layers are separated at an interlayer distance of ∼2 Å, in close agreement with the experimental findings.