Al-MCM-41 mesoporous materials (Si/Al = 27, 52, 72 and 104) were synthesised hydrothermally and characterised by XRD, FTIR, BET (surface area) and Si-29, Al-27 MAS-NMR techniques. The catalytic activity of these molecular sieves was tested in the reaction of ethylbenzene with isopropyl acetate in the vapour phase at 200, 250, 300 and 350 degreesC. Conversion of ethylbenzene decreased with increase in the temperature. The activity of these catalysts followed the order: Al-MCM-41 (27) > Al-MCM-41 (52) > Al-MCM-41 (72) > Al-MCM-41 (104). The reaction yielded alkylated and acetylated products namely 4-isopropylethylbenzene (4-IEB), 2-acetyl-4-isopropylethylbenzene (2-A-4-IEB), 2,6-diacetyl-4-isopropylethylbenzene (2,6-DA-4-IEB) and 2,4-diacetylethylbenzene (2,4-DAEB). The nature of acid sites in the catalyst was proposed to account for both alkylation and acylation. The selectivity to 4-IEB increased with increase in temperature whereas the selectivity to other products decreased. Increase in the feed ratio increased the conversion indicating the preferential adsorption of isopropyl acetate on the catalyst surface. The time on stream studies with Al-MCM-41 (27) showed nearly similar activity and selectivity for the products for 5 h. (C) 2004 Elsevier B.V. All rights reserved.