Gas phase glycerol dehydration to form acrolein over a solid acid catalyst was studied to understand the formation of by-products and to establish a detailed reaction mechanism. The experiments were conducted in an isothermal fixed bed reactor operated under various conditions (temperature, space-time velocity, concentration). From a methodological point of view, many secondary products of the reaction were passed separately over the catalyst to understand the different pathways of glycerol dehydration. Our scientific contribution to the analytical method is that all of the products were analyzed simultaneously using a multivalve on-line gas chromatograph equipped with a flame ionization detector and a thermal conductivity detector. Two products were quantified using high performance liquid chromatography, and the unknown products (2-methyl 2-cyclopenten-1-one, 3-methyl 2-cyclopenten-1-one and 2,3-butanedione) were identified by gas chromatography-mass spectrometry. Several new compounds were found. Based on the determined products, a detailed reaction mechanism was proposed. (C) 2014 Elsevier Ltd. All rights reserved.