Sunlight-driven and gram-scale vanillin production via Mn-defected γ-MnO₂ catalyst in aqueous environment

The production of vanillin from biomass offers a sustainable route for synthesizing daily-use chemicals. However, achieving sunlight-driven vanillin synthesis through H₂O activation in an aqueous environment poses challenges due to the high barrier of H₂O dissociation. In this study, we have successfully developed an efficient approach for gram-scale vanillin synthesis in an aqueous reaction, employing Mn-defected γ-MnO₂ as a photocatalyst at room temperature. Density functional theory calculations reveal that the presence of defective Mn species (Mn³⁺) significantly enhances the adsorption of vanillyl alcohol and H₂O onto the surface of the γ-MnO₂ catalyst. Hydroxyl radical (˙OH) species are formed through H₂O activation with the assistance of sunlight, playing a pivotal role as oxygen-reactive species in the oxidation of vanillyl alcohol into vanillin. The Mn-defected γ-MnO₂ catalyst exhibits exceptional performance, achieving up to 93.4% conversion of vanillyl alcohol and 95.7% selectivity of vanillin under sunlight. Notably, even in a laboratory setting during the daytime, the Mn-defected γ-MnO₂ catalyst demonstrates significantly higher catalytic performance compared to the dark environment. This work presents a highly effective and promising strategy for low-cost and environmentally benign vanillin synthesis.