POLYOXOMETALATE-BASED CATALYSTS FOR LOW-TEMPERATURE AEROBIC METHANE OXIDATION

Abstract

The oxidation of methane to methanol using molecular oxygen represents an attractive but challenging route for methane upgrading. Polyoxometalates (POMs) possess great potential as oxidation catalysts but have been underexplored for methane oxidation. Herein, a Cs+-precipitated Pd-containing phosphomolybdate (Pd/CsPMA) is first synthesized and adopted for room-temperature aerobic methane oxidation. The as-prepared Pd/CsPMA, once facilely activated by H2, converts methane and O2 almost exclusively to methanol at room temperature. Mechanism studies reveal that partially reduced PMA offers the sites for O2 and methane activation, while Pd promotes H2 activation and H spillover for PMA reduction. The following projects improve the activity of Pd/CsPMA by active site adjustments and hydrophobization. Vanadium substitution, sulfite coordination and oleylamine modification are demonstrated effective to enhance methanol productivity without hampering selectivity. The increased electron density around the active site and improved surface hydrophobicity are proposed crucial for enhancing methane activation over reduced PMA.