Highly productive iron molybdate mixed oxides and their relevant catalytic properties for direct synthesis of <i>1,1</i>-dimethoxymethane from methanol

The one-step gas phase conversion of methanol to 1,1-dimethoxymethane (DMM) was studied over highly productive iron molybdate mixed oxides in a fixed-bed reactor working at atmospheric pressure. When placing the Fe-Mo-O catalyst under a reaction mixture highly concentrated in methanol, the DMM selectivity was drastically boosted. This specific and unique feature encouraged us to extensively characterize this family of particular catalysts. LEIS analysis revealed the presence of both Mo and Fe species on the outermost atomic layer of the catalysts. X-ray photoelectron spectroscopy (XPS) and in situ EPR measurements showed that the Fe centres are responsible for the redox properties. The acidic properties of the FeMo mixed oxides were then attributed to anionic vacancies acting as Lewis acid sites produced by dehydroxylation of the catalyst surface. XPS analysis also showed that oxygen from the gas phase was responsible for reoxidation of the catalyst surface with regeneration of the active sites, which suggests a Mars-van Krevelen mechanism. The good catalytic performances were then attributed to a synergistic effect between Mo and Fe species. A Mo/Fe molar ratio of 3.2 for an optimal remarkable yield in DMM of 50% was found