Direct oxidation of CH4 to HCOOH over extra-framework stabilized Fe@MFI catalyst at low temperature

Mechanical reconstruction of Fe/ZSM-5 simultaneously leads to the decrease in crystal size and formation of high reactivity extra-framework stabilized Fe ensemble species translating from the framework or extra framework isolated Fe of zeolite. The reconstructed Fe/ZSM-5 exhibits enhanced in activity, formic acid selectivity, H2O2 efficiency and reliable stability for the direct conversion of methane to formic acid under mild conditions. [Display omitted] •Ball milling leads to reconstructions of Fe species and crystal of Fe/ZSM-5.•Isolated Fe species in ZSM-5 migrate and integrate into Fe ensemble atoms.•The crystal sizes of the treated sample significantly decrease.•The obtained catalysts showed enhanced performance for CH4 oxidation to HCOOH. Direct oxidation of methane to formic acid under mild conditions is an attractive and challenging topic for methane upgrade. Fe-containing MFI-type zeolite (ZSM-5) has been recognized as a potential catalyst for this reaction. Herein, we demonstrate a simple method to crack the Fe/ZSM-5 into nanosized crystals and translate the isolated Fe3+ located in or outside the framework to extra-framework Fe ensemble species (dimer, oligomer and cluster) through high energy ball milling. The resultant catalysts exhibit up to 148% times increase in activity and provide higher formic acid selectivity and reliable stability for methane direct oxidation to formic acid with H2O2 as oxidant. The turnover frequency of C1 products over a 0.03%Fe/ZSM-5 catalyst is as high as 8380 h−1 with 96% of formic acid selectivity at 70 °C. Our work provides a valuable example for the design of an efficient catalyst for methane oxidation or even other light hydrocarbon carbohydrate oxidation processes.