Grafting of Al onto purely siliceous mesoporous molecular sieves

Abstract

Aluminosilicate mesoporous molecular sieves exhibiting excellent structural ordering and enhanced acidity and catalytic activity have been prepared by reacting purely siliceous materials with Al-alkoxide in non-aqueous media. The Al is inserted into the framework of the purely siliceous parent material (MCM-41 or MMS) to generate (Brønsted) acid sites whose content is higher than in equivalent Al-MCM-41 materials prepared via the conventional direct mixed-gel synthesis method. ²⁷Al MAS NMR and XPS confirm that the Al is incorporated into the solid framework where it adopts 4-coordinate symmetry. Bulk structural characterisation (using XRD and BET) shows that the hexagonal structure of the parent purely siliceous material is maintained during the grafting procedure with no loss of long range structural ordering. The resulting Al-grafted materials possess considerable catalytic activity for Brønsted acid catalysed cracking of cumene.