Selective oxidation of methane into formaldehyde and carbon monoxide catalyzed by supported thermally stable iron oxide subnanoclusters prepared from a diiron-introduced polyoxometalate precursor

Direct oxidative conversion of methane (CH 4 ) into useful C1 products remains challenging due to the low reactivity of CH 4 and its facile overoxidation into carbon dioxide (CO 2 ) under high temperature conditions. Iron oxide (FeO x ) cluster catalysts are promising because of their low activation energy for CH 4 oxidation. However, preliminary results revealed that FeO x clusters were easily aggregated and deactivated under CH 4 oxidation conditions at 873 K. In this study, we used a diiron-introduced polyoxometalate as a precursor to form thermally stable FeO x subnanoclusters on SiO 2 , which selectively converted CH 4 into formaldehyde (HCHO) and carbon monoxide (CO) (CH 4 conversion, 2.3%; HCHO and CO selectivity, 87% at 873 K after 1 h). The FeO x subnanocluster catalyst maintained catalytic activity even after 72 h. Various characterizations, such as STEM, X-ray absorption spectroscopy, and X-ray diffraction, revealed that the in situ formed FeO x subnanoclusters were stabilized by WO x nanoclusters originating from the polyoxometalate frameworks. • A diiron-introduced polyoxometalate ( Fe2 ) was employed as a precursor. • A thermally stable SiO 2 -supported FeO x subnanocluster was formed at 873 K. • Fe2 /SiO 2 exhibited 87% selectivity to HCHO and CO at 2.3% CH 4 conversion. • Fe2 /SiO 2 maintained the catalytic activity even after 24 h.