Methanol oxidation on Fe2O3 catalysts and the effects of surface Mo

Abstract

The adsorption of methanol on haematite has been investigated using temperature programmed methods, combined with in situ DRIFTS. Model catalysts based on this material have then been made with a shell–core configuration of molybdenum oxide monolayers on top of the haematite core. These are used as models of industrial iron molybdate catalysts, used to selectively oxidise methanol to formaldehyde, one of the major chemical outlets for methanol. Haematite itself is completely ineffective in this respect since it oxidises it to CO₂ and the DRIFTS shows that this occurs by oxidation of methoxy to formate at around 200 °C. The decomposition behaviour is affected by the absence or presence of oxygen in the gas phase; oxygen destabilises the methoxy and enhances formate production. In contrast, when a monolayer of molybdena is placed onto the surface by incipient wetness, and it remains there after calcination, the pathway to formate production is blocked and formaldehyde is the main gas phase product in TPD after methanol dosing.