The Nature of the Molybdenum Surface in Iron Molybdate. the Active Phase in Selective Methanol Oxidation

The surface structure of iron molybdate is of great significance since this is the industrial catalyst for the direct selective oxidation of methanol to formaldehyde. There is a debate concerning whether Fe₂(MoO₄)₃ acts as a benign support for segregated MoO₃ or if there is an intrinsic property of the surface structure which facilitates its high catalytic efficacy. This study provides new insights into the structure of this catalyst, identifying a bound terminating layer of octahedral Mo units as the active and selective phase. Here we examine whether only 1 monolayer of Mo on iron oxide alone is efficacious for this reaction. For a 1 ML MoO_x shell-Fe₂O₃ core catalyst the Mo remains at the surface under all calcination procedures while exhibiting high selectivity and activity. The work highlights how catalyst surfaces are significantly different from bulk structures and this difference is crucial for catalyst performance.