Synthesis and pore system modification of large MFI-type zeolite crystals for IR microscopic diffusion studies

MFI type zeolites cover an important role in industrial applications as catalysts and molecular sieves thanks to their acid character and high surface area in virtue of their extreme porosity. However, small pore dimensions constrain molecular diffusion and hinder full utilization of the material. The introduction of additional, higher order porosity with a size gradient arrangement gives place to hierarchical porous systems and helps improve molecular diffusion in the zeolite. Additionally, real diffusional behaviour can be investigated by microscopic techniques such as Infrared Microimaging (IRM), being able to give accurate information by recording molecular concentration profiles over time or over space. Nevertheless, the current available instruments suffer from several technical limits, with insufficient resolution on crystals with dimensions <20 μm being the most relevant one. In the present work, micrometre sized MFI-type zeolite crystals are purposefully synthesized in order to be later studied at IRM and variations to the reaction members are attempted in order to improve the synthesis. The introduction of additional mesoporosity and zeolite hierarchization are attempted by applying post treatments of etching and desilication, aimed at leaching of Al and Si cations. Subsequently, the diffusion behaviour of some probe molecules is investigated at IRM on parent and post-treated self synthesized MFI samples.