Decoupling mesoporosity formation and acidity modification in ZSM-5 zeolites by sequential desilication-dealumination

The combination of dealumination and desilication of ZSM-5 zeolites has been investigated in order to decouple mesoporosity creation and modification of acidity. Individually, desilication by treatment in alkaline medium leads to a spectacular mesoporosity development, without distinct modification of the acidic properties, while dealumination by steam treatment mainly impacts on the acidity of the ZSM-5 zeolite. It is shown that application of the alkaline treatment first followed by steam treatment results in MFI zeolites with independently tailored pore architecture and acidic properties, with proven hydrothermal stability under severe conditions. The independent modification of porous and acidic properties cannot be accomplished if the alkaline treatment is performed after the steam treatment, since the presence of extra-framework Al species inhibit Si extraction and related mesopore formation. A promising outlook of the successive alkaline-steam treatment is expected in catalytic applications of microporous materials. (c) 2005 Elsevier Inc. All rights reserved.