From Layered Zeolite Precursors to Zeolites with a Three-Dimensional Porosity: Textural and Structural Modifications through Alkaline Treatment

The layered zeolite precursor RUB-36, consisting of ferrierite-type layers, can be transformed into a three-dimensional framework through various methods such as topotactic condensation into the CDO topology, or interlayer expansion either in the presence or absence of a silylating agent. However, the plate-like morphology of the micrometer sized crystals hampers the accessibility of the 2D micropore system, in which the channels run parallel to the plates. With the aim of introducing mesoporosity, alkaline treatments were performed on different RUB-36 derived expanded materials, and on RUB-36 itself. The effect on the physicochemical properties was examined using N2 physisorption, powder X-ray diffraction, scanning electron microscopy and 27Al MAS NMR whereas the influence on the catalytic activity was evaluated using esterification and alkylation reactions. After calcination, the purely inorganic, interlayer expanded material could be transformed into a mesopore containing FER-type material by selective removal of the interlayer T atom followed by the recombination of the layers. In the precalcination state, organic moieties, originating from the silylating agent or from the organic structure directing agent (OSDA), increase the hydrophobicity of the interlayer expanded structure and its stability against the alkaline treatment. In RUB-36, the high OSDA content limited the amount of mesopore formation through alkaline treatment. However, using the appropriate conditions, the subsequent interlayer expansion of alkaline treated RUB-36 also resulted in a mesopore containing interlayer expanded structure.