Adsorption and dehydration of methanol on Al₂O₃ catalyst

The relationship between the structure and the catalytic activity of the methanol dehydration catalyst of Al₂O₃ with high activity prepared by different methods was studied. The reaction mechanism of methanol dehydration on the catalyst was described. The primary crystal structure of the catalyst consisted of γ-Al₂O₃ and amorphous Al₂O₃ with two types of Lewis acid sites, σ_I and σ_II, instead of Brönsted acid sites, existing on the catalyst surface, which play important roles in the methanol dehydration. There were two adsorption states of methanol on Lewis acid sites of the catalyst, i.e., the molecular adsorption state and the dissociative adsorption state. The molecular adsorption of methanol on the catalyst was reversible, while the dissociative adsorption of methanol was irreversible. The dissociatively adsorbed methanol could further decompose to form CO, H₂, little CO₂, CH₄, and C. The reaction of the molecularly adsorbed methanol with the dissociatively adsorbed methanol led to the formation of dimethyl ether.