Magnetically tunable selectivity in methane oxidation enabled by Fe-embedded liquid metal catalysts

As they are liquids at room temperature, gallium-based metal substrates allow catalytic metal atoms to move freely without lattice constraints, thereby facilitating the development of catalysts with reconfigurable structures. Here we design an iron-embedded liquid metal catalyst that enables reversible switching of the aggregation and electron spin of iron atoms by controlling an external magnetic field. This facilitates a reversible conversion of the primary liquid products, methyl hydroperoxide (CH₃OOH) and acetic acid (CH₃COOH), under ambient conditions. The catalyst achieves promising production rates (CH₃OOH, 1,679.6  $mmol{g}_{Fe}^{-1}{h}^{-1}$ ; CH₃COOH, 790.5  $mmol{g}_{Fe}^{-1}{h}^{-1}$ ) and high selectivities (CH₃OOH, 99.9%; CH₃COOH, 91.7%). In the absence of the magnetic field, iron atoms are atomically dispersed, leading to the C1 pathway without C-C bond coupling. When a magnetic field is applied, iron atoms cluster, favouring CH₃COOH production in the C2 pathway. The product distribution can be finely and reversibly tuned with magnetic field intensity adjustments ranging from 0 to 500 G. Our findings highlight the potential for using an external magnetic field to precisely control catalytic pathways.