Methanol adsorption and activation by zeolitic protons

Density functional theory is used to determine the modes of adsorption at low and high coverage of methanol as well as the intermediates involved in the Brønsted acid methanol dehydration to dimethyl ether. Two different reaction pathways were studied. In the first, methanol adsorption and surface methoxy species formation are the initial elementary steps for this reaction. Subsequent dimethyl ether formation by reaction of methanol with the surface methoxy species takes place. The second path involves the simultaneous adsorption and activation of two methanol molecules with formation of dimethyl ether and water in one step. The latter appears to be the preferred route. Additionally, carbon-carbon bond formation from the activation of methanol or dimethyl ether molecules by the surface methoxy groups was studied. The products are ethanol and ethyl methyl ether. Computed infrared spectra of the adsorption of one and two methanol molecules to a zeolitic proton are discussed.