New reaction pathways and kinetic parameter estimation for methanol dehydration over modified ZSM-5 catalysts

Kinetics of the methanol (MeOH) dehydration has been investigated using two kinds of alkali metal-modified ZSM-5 (mZSM-5) catalysts, which were developed for the purpose of preparing dimethyl ether (DME) from water-containing MeOH. Two intrinsic kinetic mechanisms have been suggested and rigorous reaction rate equations were derived based on a series of reaction experiments in the presence and in the absence of water. In addition to the kinetic parameters, the heats of adsorption of MeOH and water were successfully estimated. The values are in good agreement with those obtained from the previously reported experimental results. According to the reaction pathways of our concern, two adsorbed MeOH molecules on the mZSM-5 simultaneously react with acidic sites to produce the intermediate molecule, which then undergoes the rate-determining step that the intermediate molecule rearranges itself to split into the smaller intermediates for the next step with or without the abstraction of water. In addition, the existence of the crucial intermediate closely related to the rate-determining step was also confirmed through FT-IR spectroscopy.

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► Kinetic mechanisms on the alkali metal modified ZSM-5 catalysts.
► Simultaneous adsorption and activation of two methanol molecules.
► Presence of the methyl carboxonium ion.
► The kinetic parameters and the heats of adsorption were successfully estimated.