Mesoporous Al-MCM-41 molecular sieves in the Si/Al ratios 33, 52, 72 and 114 were synthesised under hydrothennal condition. They were characterized using powder X-ray diffraction (XRD), FF-IR, BET and thermogrivimetric-differential thermal analyser (TGA-DTA). The XRD spectra showed that the materials were of hexagonal mesoporous structure, The FT-IR spectra revealed (lie order of hydrophobic character of the catalyst materials by comparing the broad envelope due to the O-H stretching of' water in the higher energy region. The acidity of the catalyst was measured by FT-IR using pyridine as the diagnostic base. The BET surface area measurements indicated (lie surface areas between 900 and 1000 m(2)/g and pore diameter around 26 A units. The catalytic activity of the materials was tested for the vapour phase esterification of acetic acid and n-butanol under autogenous condition. The effect of reaction temperature. mole ratio of' (lie reactant. time and catalyst loading on n-butanol conversion and selectivity of n-butyl acetate was studied and the results are discussed, Al-MCM-41 (33) was found to be more active than the other catalysts owing to its high density of' Bronsted acid site,,, The reaction was also influenced by the hydrophobic property of the catalyst, as the conversion over Al-MCM-41 (114) is nearly equal to Al-MCM-41 (33), The requirement of Bronsted acid sites for the reaction was clearly established by running the reaction in the absence of catalyst. Occurrence of the reaction mainly within the pores was confirmed by running the reaction over the as-prepared catalyst that provides 60% less conversion than the calcined material. The reaction was also studied over H-Mordenite, H-beta, H-ZSM-5 and HY zeolites, and the result,, are compared. (c) 2005 Elsevier B.V. All rights reserved.