Review: Dehydration Catalysts for the Methanol/Dimethyl Ether Reaction

Catalysts for the methanol/dimethyl ether reaction are reviewed with particular emphasis on the acid/base properties of the catalysts. The focus is on temperatues less than around 300°C and atmospheric pressure conditions, which correspond to potential automotive applications. Mechanisms including both dual site (acid/base) Langmiur-Hinshelwood and single site Rideal-Eley mechanisms have been postulated, with both Bronsted and Lewis acid sites involved in the dehydration reaction. Temperatures higher than about 300°C, as well as a strong surface acidity, tend to promote the further dehydration of DME to form C2-Q5 olefins and eventually hydrocarbon products in a series type reaction sequence. Methods exist, particularly in zeolites, to control the strength and type of surface acidity, and therefore the selectivity to DME.