Iron molybdates are known to be efficient catalysts for the oxidation of methanol to formaldehyde and they comprise MoO3 and Fe2(MoO4)3 phases with different Mo:Fe bulk ratios. However, we recently extended the application of these materials, by employing MoO3/Fe2(MoO4)3 for the partial oxidation of K-decane in the gas phase. In particular, we identified that at low temperature (350 °C) the catalyst produced oxygenated aromatics, while at high temperature (460 °C) non-oxygenated products were obtained (Scheme 1). In order to explain this counterintuitive behavior, in situ XRD and a series of surface methods including diffuse reflectance UV-Vis spectroscopy, Raman spectroscopy, and SEM-EDX were used to determine the structural modifications of the catalyst under the reaction conditions. It was possible to identify the different reactivity associated with different iron molybdate phases, namely Fe2(MoO4)3 and FeMoO4. In addition, the surface of the catalyst was extremely sensitive to the amount of oxygen present in the reaction atmosphere, thus allowing a switch from oxygenated to non oxygenated products.
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