Tuning Hydrophilicity and Active Sites of Fe-ZIF-8 to Enhance Methane-to-Formic Acid Conversion under Mild Conditions.

Direct selective oxidation of methane to formic acid (HCOOH) under mild conditions remains a major challenge. Here, we reported a surfactant-assisted in situ modification strategy that tuned the surface hydrophilicity and Fe active sites of Fe-ZIF-8. Among the three surfactants investigated, C16-modified FZ@C16 exhibited the lowest hydrophilicity and the highest proportion of mononuclear Fe species while preserving the ZIF-8 framework integrity. The moderately hydrophobic surface enhanced CH4 adsorption and local enrichment near active sites, improving the utilization efficiency of •OH radicals generated from H2O2 activation. Consequently, FZ@C16 achieved a HCOOH yield of 54.1 μmol with a TOF of 75 h-1 and a selectivity of 93.9% at 50 °C under 3 MPa CH4, surpassing previously reported MOF-based catalysts. This work demonstrates that surface wettability regulation offers a feasible promising strategy for designing non-noble metal catalysts for methane oxidation.