A Mechanistic Study of the Methanol Dehydration Reaction on γ-Alumina Catalyst

Article abstract of DOI:10.1021/j100126a017

The dehydration of methanol over a porous γ-Al2O3 catalyst was studied using periodic square-wave modulation of the feed to a microcatalytic reactor.Online mass spectrometry was used to obtain wave forms at the exit of the reactor for methanol, dimethyl ether, water, and a carrier gas.The reaction was studied over the temperature range of 230-350 deg C.At lower temperatures, the dimethyl ether wave form went first through a maximum, decreased to a constant level during the on cycle, and then went through a second maximum at the beginning of the off cycle.At higher temperatures where the conversions increased, the relative intensity of the maximum to the level part of the wave form continuously decreased until no maximum could be observed at temperatures above 280 deg C.Water was found to have a phase lag of about 4 s with respect to dimethyl ether over the studied temperature range.The shape of the wave forms was explained in terms of a reaction mechanism which involved reactions of surface species formed from the adsorption of methanol on the γ-Al2O3 surface.The species considered were molecularly adsorbed methanol, methoxy, and hydroxyl groups.The mechanism contained two parallel reaction pathways for the production of dimethyl ether.One pathway was the reaction between molecularly adsorbed methanol and methoxy species, and the other was the reaction between two methoxy species.For the production of water, only a single step of recombination of surface hydroxyls was considered in the mechanism.Equations for the material balances of the species considered in the mechanism were numerically integrated to generate wave forms with the same shape as observed in the experimental data.