W. Pudlo, V. Pashkova, M. Derewinski, A.B. Jarzebski
Materials with multimodal hierarchical porosity, containing pore networks in the range of micro-, meso- and macropores, attract considerable attention owing to their widespread application prospects in process industries (catalysts, sorbents), energy conversion and sensors. Here we present a new, effective procedure for the preparation of the silica-alumina monoliths with a micrometric flow-through pores and containing MFI-type zeolitic films. These materials are fabricated by a hydrothermal treatment of a parent meso/macroporous silica-alumina monoliths fabricated by the Nakanishi method, to form a microporous layer of the MFI structure. The parent silica-alumina monoliths were synthesized by inducing phase separation parallel to the sol-gel transition. Concentrated solution of TPAOH (40 wt%) was used to impregnate the parent solid and provide the templates necessary to obtain MFI-type microcrystalline zeolitic films. The process of transformation and the properties of the new materials were investigated by means of XRD, SEM, TEM and nitrogen adsorption measurements. XRD analysis confirmed the presence of a sole crystalline phase of MFI-type whereas nitrogen adsorption experiments showed a considerable change in the pore structure at nanometric scales. Further investigations (NMR and FTIR) and catalytic tests will aim at determining the structural properties in molecular scales, surface acidity and catalytic properties.