Transformation Control of a Layered Zeolite Precursor by Simple Cation Exchange

Abstract

The topotactic transformation of layered zeolite precursors to threedimensional zeolite frameworks is of major importance because it is a viable option for finding new zeolite structures. Here, we report the synthesis of a new CDO zeolite precursor with a Si/Al ratio of 6.5, named PST-23, using 4-(dimethylamino)1-methylpyridinium (DMAMP(+)) ions as an organic structure-directing agent in fluoride media. We also show that the ion exchange of the as-synthesized DMAMPPST-23 with inorganic and organic cations smaller than DMAMP(+) followed by calcination at 600 degrees C leads to the transformation into FER and CDO zeolites, respectively. The overall characterization results demonstrate that cation exchange in the as-synthesized PST-23 leads to significant changes in the local environment of framework tetrahedral sites, as well as a notable decrease in the interlayer distance, which allows its topotactic transformation to occur in different ways, without the initial swelling step. We have also generated three novel hypothetical zeolite structures built from fer, heu, and cas layers, which are chemically feasible and thus synthesizable.