Synthesis of MCM-48 granules with bimodal pore systems via pseudomorphic transformation of porous glass

5 years ago

Synthesis of MCM-48 granules with bimodal pore systems via pseudomorphic transformation of porous glass

It was shown in previous publications that porous glasses can be transformed into MCM-41 materials with monomodal or bimodal (hierarchical) pore systems. In this study we describe the synthesis of MCM-48 granules with a bimodal pore structure via pseudomorphic transformation of porous glasses. Due to the cubic network of the MCM-48 structure, such materials are characterized by an improved mass transfer inside the pores compared to the 2 dimensional MCM-41 pore system. This represents an advantage for applications as catalyst support. Porous glass granules (100–200 μm particle size) with a pore diameter of 150 nm and a pore volume of 1.44 cm³/g were used as starting materials. The transformation process was controlled via different concentrations of cetyltrimethylammoniumhydroxide (CTAOH). The products were characterized by nitrogen adsorption, mercury intrusion, x-ray diffraction, scanning electron microscopy and light microscopy. The results confirmed the successful synthesis of MCM-48 particles with a hierarchical pore structure. The starting pore system with 150 nm diameter disintegrated during the transformation process because of the formation of MCM-48 clusters. A new pore system with approximately 3000 nm in diameter was formed among these clusters. A cavitation effect was observed during nitrogen adsorption/desorption measurements. This indicates that some parts of the starting pore system were entrapped by MCM-48 clusters. This can be explained with the higher concentration of the surfactant solution during transformation of the starting glass into the MCM-48 phase, which leads to a higher solubility and mobility of the silica source. Furthermore, the dependence of the quality of synthesized MCM-48 concerning geometry and structure of the starting materials was investigated by transformation of AEROSIL^® 200. Due to the particulate and non-porous character of this starting material just a minor cavitation effect was observed during the physisorption measurements.

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DOI: S1387181117305693