Sulfite-Enhanced Aerobic Methane Oxidation to Methanol over Reduced Phosphomolybdate

H₂-reduced phosphomolybdate (PMA) demonstrated promising aerobic selective methane oxidation activity at room temperature. However, this catalytic system remains limited by insufficient methane activation efficiency at the molybdenum (Mo) sites. Here, we introduce inorganic sulfite anions as a promoter to enhance the H₂-treated heterogeneous palladium (Pd)-containing Pd/CsPMA catalyst. With the optimal sulfite addition, the methanol productivity was improved by more than 4 times without compromising high methanol selectivity. Spectroscopic techniques and theoretical calculation imply that sulfite serves as a modification ligand, binding to exposed Mo sites from the on-top or bridge locations. This alters the redox properties of PMA, facilitating the creation of more reactive oxygen species for hydrogen abstraction from methane.