Friedel-Crafts catalysis using supported reagents - Synthesis, characterization and catalytic applications of sol-gel-derived aluminosilicates

Aluminosilicate catalyst supports have been prepared from aluminium tri-sec-butoxide and tetraethyl orthosilicate in butanol using sol-gel methodologies, thereby providing useful supports for zinc chloride, to generate heterogeneous Friedel-Crafts alkylation catalysts. The optimum loading for these sol-gel-derived materials is higher than that of K10, the support for the commercially available catalyst 'Clayzic' and gives significantly higher catalytic activity in a standard test reaction. A more convenient, 'one-pot' approach, in which zinc chloride is added during the sol-gel synthesis, generates catalysts which also show significantly higher activity than Clayzic. The resulting materials have been characterized by Si-29 cross-polarization magic-angle spinning (CP-MAS) and Al-27 MAS NMR, IR spectroscopy and by surface area and pore volume analysis. The Si:Al ratio, drying temperature and relative amounts of water and (non-aqueous) solvent have pronounced effects on catalytic activity. The most active catalysts show relatively high levels of framework aluminium species compared with non-framework sites, and also have higher surface areas and pore volumes than materials with lower activity.