Surfaces of nano-sized ZSM-5 zeolites have been passivated by a chemical liquid deposition (CLD) technique using tetraethylorthosilicate (TEOS). The impact of this post-synthesis treatment has been evaluated in the methanol-to-olefins (MTO) reaction. A two-step surface passivation led to enhanced selectivity towards C-2-C-4 light olefins, between 10 and 30% in relative, at nearly complete methanol conversion when compared with pristine zeolites. However, these post-treated zeolites exhibited a significant loss in stability. To rationalize these results and establish structure-activity relationships, zeolite catalysts have been thoroughly characterized by nitrogen adsorption-desorption, SEM, XRF, XRD and FIR techniques. ZSM-5 zeolite (Si/Al = 27) in the form of well-arranged rectangular nanocrystals behave in MTO after silylation as a commercial ZSM-5 zeolite having a Si/Al = 52. (C) 2015 Elsevier B.V. All rights reserved.