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

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 Cl products over a 0.03%Fe/ZSM-5 catalyst is as high as 8380 h(-1) with 96% of formic acid selectivity at 70 degrees 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.

Automated summary

The study demonstrates a simple method to crack Fe/ZSM-5 into nanosized crystals and convert isolated Fe3+ into extra-framework Fe ensemble species, resulting in higher catalyst activity and selectivity for methane oxidation to formic acid. The catalysts show a significant increase in turnover frequency and provide a valuable example for designing efficient catalysts for methane oxidation processes.