Light olefin transformation over ZSM-5 zeolites with different acid strengths - A kinetic model

In this study, we analysed the influence of the acidity of a ZSM-5 catalyst on the catalytic transformation of various short-chain olefins (ethylene, propylene and 1-butene). Four ZMS-5 catalysts with different acid strength distributions were studied at different temperatures and partial pressures. The results were fitted using a kinetic model based on a network mechanism, which details the products by type (olefins, paraffins and aromatics) and number of carbon atoms. Polanyi-type equations, supported on quantum chemical calculations, were used to derive quantitative relations between the ammonia adsorption energy, used as a measure of the acidity of a given acid site, and the energetics of the various steps involved in the reaction. It was observed that, although the qualitative aspects of the reactivity differs from olefin to olefin and according to the catalyst's acidity, the model is able to describe both activity and product distribution for all catalysts, reactants and conditions using a single reaction scheme and a single set of kinetic parameters. (C) 2010 Elsevier B.V. All rights reserved.