Search

[Display omitted] • Fe 2 O 3 - c and Fe 2 O 3 - h nanocrystals were prepared through the calcination of Fe-MOF. • Fe 2 O 3 - c nanocrystals have better DOMF performance than Fe 2 O 3 - h nanocrystals. • The phase engineering of Fe 2 O 3 affects CH 4 adsorption ability during DOMF process. The direct oxidation of methane (CH 4) under mild conditions is a highly desirable technology to achieve the low-carbon and atom-economic production of high-value-added C1 oxygenates. However, the difficult activation of the C H bond of CH 4 and the overoxidation of C1 oxygenates to carbon dioxide (CO 2) are still the major bottlenecks. Herein, we systematically investigate the phase engineering of Fe 2 O 3 in dependence on the performance of the direct oxidation of CH 4. The cubic phase of Fe 2 O 3 (Fe 2 O 3 - c) nanocrystals enables the direct oxidation of CH 4 to HCOOH (DOMF) under mild aqueous conditions, and the HCOOH yield and selectivity could reach 6.315 mmol g cat −1 h−1 and 89.4%, which are 69.3 and 1.34 times higher than those of the hexagonal phase of Fe 2 O 3 (Fe 2 O 3 - h) nanocrystals. Mechanism experiments indicate that Fe 2 O 3 - c nanocrystals can optimal CH 4 adsorption behavior, favoring to the occurrence of the DOMF. In addition, in situ DRIFTS demonstrates that the DOMF is the radical reaction process that the activation of C H bond is caused by the ·OH radical. Subsequently, the unstable CH 3 OOH and stable CH 3 OH intermediates undergo further oxidation to form HCOOH. This work offers the phase engineering strategy to enhance the catalytic performance and reveal the reaction mechanism for the direct oxidation of CH 4. [ABSTRACT FROM AUTHOR]