Molybdenum oxide supported on mordenite zeolite-alumina composite is post-treated by nitric acid leaching with varying periods (12-48h). The post-treated molybdenum catalysts display much higher stability for propene formation in 1-butene metathesis reaction. The evolution of Mo species has been characterized by laser Raman, (27)AI MAS NMR and X-ray photoelectron spectroscopy. Characterization results have shown the extraction of aluminum molybdates (Al-2(MoO4)(3)) after acid leaching post-treatment. This structural transformation relates to a transition in coke species on the spent molybdenum catalysts, and leads to the improvement in metathesis stability. (C) 2011 Elsevier B.V.. All rights reserved.