A concise and systematic study of the hydrothermal synthesis of Si-MCM-48: Structural aspects and mechanical stability

Abstract

The structural collapse of mesoporous molecular sieve Si-MCM-48 by mechanical compression was investigated. Samples were synthesized by modifying temperature and time of a hydrothermal synthesis, according to a 32 experiment design. In this way, flexibility of the synthesis method was evaluated. Structural and textural characteristics were investigated using X-ray diffraction, nitrogen physisorption, and scanning and transmission electronic microscopies. As a consequence of the increase in applied pressure, different behavior was observed in the average wall thickness of samples related to the porous organization of the solid. The collapse of interparticular macropores caused a greater increase in thickness at low compression pressures, while the intraparticular mesopores, supported by the silica walls, supported greater compression. The macropores collapsed by mechanical compression at pressures as low as 60 MPa, while mesoporous ones exhibited reasonable resistance up to 200 MPa. Samples synthesized with high temperatures and long reaction times presented better mechanical resistance due to the favorable kinetics of silica condensation on the walls and, thus, are more interesting for applications in catalysis or adsorption.