LAUSR

Aqueous-phase oxidation by H2O2, known as the Fenton-type process, provides an attractive route to convert recalcitrant lignin derivatives to valuable chemicals under mild conations. The development of this technology is, however, limited by the uncontrolled selectivity, resulting from the highly reactive nature of H2O2 and the thermodynamically favored deep oxidation to form CO2. This study demonstrates that formic acid can be produced with a high selectivity (up to 80.3% at 313 K) from the Fenton-type oxidation of guaiacol and several other lignin derivatives over a bimetallic Fe-Cu catalyst supported on a ZSM-5 zeolite. Combined experimental and theoretical investigations unveil that the micropores of the zeolite support, which contains active metal sites, prefer to adsorb C2-C4 intermediates over formic acid because of its stronger dispersive interaction with larger guest molecules. This confinement effect significantly suppresses the secondary oxidation of formic acid, accounting for the uniquely high formic acid selectivity over Fe-Cu/ZSM-5.