Finding the Right Synergy of Iron and Molybdenum in Mixed Metal Oxide Catalysts for the Sustainable Production of Acetaldehyde via Oxidative Dehydrogenation of Ethanol

Iron–molybdenum mixed oxides are well-established catalysts for the oxidative dehydrogenation (ODH) of methanol, but their performance in the ODH of ethanol (EtOH), particularly with respect to the Mo:Fe ratio, remains unexplored. In this study, we present the synthesis of mixed oxides across the full composition range, their catalytic assessment in the ODH of EtOH, and their structural characterization. While pure iron oxide is unselective toward acetaldehyde (AcH), introducing small amounts of molybdenum oxide enhances the catalyst's selectivity significantly. In contrast, molybdate-rich systems tend to produce more dehydration products such as diethyl ether and ethene due to an increased acid site density. The optimal catalyst was found to be an iron-rich system with a composition of x_Fe = 0.95, yielding 94% AcH at temperatures as low as 220 °C with promising long-term stability. Therefore, while molybdenum is essential for high catalytic activity and selectivity, only small amounts are required when supported by a high surface area, defect-rich iron oxide, highlighting the efficiency of this mixed oxide system as catalyst for the ODH of EtOH.