Surface species in the methyl formate-methanol-dimethyl ether-gamma-Al2O3 system studied by in situ IR spectroscopy

The interconversions of species on the gamma-Al2O3 surface in the methyl fo rmate-methanol-dimethyl ether system were studied by in situ IR spectroscop y. During methyl formate transformations at 100-300 degrees C, the formatio n of two surface species was detected: formate and an adsorbed formaldehyde complex. These species were also detected in methanol transformations, esp ecially in the presence of oxygen. Formaldehyde was detected in trace amoun ts in the products from methanol transformation, where the main product was dimethyl ether. Formaldehyde is formed by methanol oxidation over gamma-Al 2O3. Using a flow cell (reactor), temperature and concentration dependences were traced for reactants, products, and surface species. A probable mecha nistic scheme of methanol transformations includes the formation of dimethy l ether via the reaction of two methoxy groups. Formaldehyde is formed via the oxidation of a methoxy group by oxygen activated on the surface defects of alumina.