Influence of the Preparation Conditions on Textural and Chemical Properties of Hexagonal MSU-3

Different mesoporous MSU-3 silicas with hexagonal symmetry can be synthesized using the non-ionic block copolymer, Pluronic P123, as structure directing agent and NaF as condensation catalyst. [Si]-MSU-3 has a bimodal pore system with larger mesopores of 6.6 to 7.7 nm and smaller mesopores of 3.5 nm diameter. The size of the larger mesopores can be varied by hydrothermal treatment under acidic pH whereas the smaller pores are not affected by this treatment. Before hydrothermal treatment, the material has a worm hole-like porous framework with pores of 3.7-4.1 nm. When aluminium sulfate or nitrate was used as condensation catalyst, some aluminium was incorporated into the silica framework, lending acidity to the sample. Transmission electron microscopy shows that these [Al]-MSU-3 materials contain a complex network of well-ordered hexagonal as well as disordered wormhole pores. They exhibited good catalytic activity for liquid phase Friedel Crafts benzylation of p-xylene.