The gas phase alkylation of toluene with propylene was used to investigate the catalytic activity of pure zeolite Beta, pure mesoporous molecular sieve Al-MCM-41 and micro/mesoporous composites. The influence of the structural features and the concentration of acid sites of these catalysts on the toluene conversion and the selectivity to isopropyltoluenes (cymenes) was studied. Various characterization techniques, i.e., DLS, SEM, XRD, FT-IR, NMR, and nitrogen sorption measurements were applied for complete characterization of the catalysts. In addition, the concentrations of Bronsted and Lewis acid sites were determined based on the amount of adsorbed d(3)-acetonitrile using FT-IR spectroscopy. The catalytic activity in toluene alkylation with propylene was increased in the order: Al-MCM-41 < micro/mesoporous composites < commercial zeolites Beta < nanosized zeolite Beta. This sequence clearly shows the role of strong Bronsted acid sites in the reaction together with the decrease in the transport limitations with decreasing size of zeolite crystals. The enhancement of toluene conversion over micro/mesoporous composites compared to Al-MCM-41 is due to the presence of zeolite particles in composite catalyst increasing the acidity of this material. (c) 2004 Elsevier B.V. All rights reserved.