Four ZSM-5 zeolite materials with varying crystal size, acid site density and morphology were prepared, characterized by BET, XRD, SEM, FT-IR, H/D exchange and n-hexane cracking experiments and tested as catalysts for the Methanol to Olefins (MTO) reaction at 350 degrees C, WHSV = 1.8 g/gh under atmospheric pressure. Optimal propene to ethene ratios (>5) were obtained over a material prepared via the fluoride route. Its superior selectivity was tentatively ascribed to its low density of strong acid sites in combination with a long diffusion pathway and few crystal defects. (C) 2012 Elsevier B.V. All rights reserved.