Mesoporous aluminosilicate materials have previously had the disadvantage of being structurally less stable than zeolites, which are crystalline and more ordered. A new approach to Al-containing MCM-41 is presented here: This two-step synthesis procedure involves adding Al to the synthesis gel during a second crystallization step, which ensures the incorporation of Al as an aluminosilicate layer at or near the surface of the pore walls of existing MCM-41 crystallites, resulting in Al-MCM-41 materials with good hydrothermal and mechanical stability and enhanced ion-exchange capacity.