Selective photooxidation of methane to C1 oxygenates by constructing heterojunction photocatalyst with mild oxidation ability

Abstract

Selective photocatalytic aerobic oxidation of methane to value-added chemicals offers a promising pathway for sustainable chemical industry, yet remains a huge challenge owing to the consecutive overoxidation of primary products. Here, a type II heterojunction were constructed in Ag-AgBr/ZnO to reduce the oxidation potential of stimulated holes and prevent the undesirable CH₄ overoxidation side reactions. For photocatalytic oxidation of methane under ambient temperature, the products yield of 1499.6 μmol g_cat⁻¹ h⁻¹ with a primary products selectivity of 77.9% was achieved over Ag-AgBr/ZnO, which demonstrate remarkable improvement compared to Ag/ZnO (1089.9 μmol g_cat⁻¹ h⁻¹, 40.1%). The superior activity and selectivity result from the promoted charge separation and the redox potential matching with methane activation after introducing AgBr species. Mechanism investigation elucidated that the photo-generated holes transferred from the valence band of ZnO to that of AgBr, which prevent H₂O oxidation and enhance the selective generation of •OOH radical.