N-Doped Carbon Nitride with Embedded Pd Nanoparticles for Selective Photocatalytic Valorisation of Biomass-Derived Vanillin into Vanillyl Alcohol and 2-Methoxy-4-Methyl Phenol

Efficient conversion of abundant biomass into high-value chemicals is crucial for sustainable chemical production. Herein, we report the design and synthesis of a Pd nanoparticles (NPs)-embedded N-doped carbon nitride (Pd@NCN) nanocomposite for the photocatalytic transformation of biomass-derived compounds. N-doping of carbon nitride using DMF significantly enhanced visible light absorption, as evidenced by DRUV spectroscopy, making it a suitable photocatalyst for blue LED-driven reactions. Subsequent decoration with Pd NPs remarkably improved the catalyst's performance. UPS measurements revealed that Pd NPs, with their lower Fermi level and higher work function compared to the photoactive support, act as efficient electron acceptors, promoting charge separation and improving the catalytic activity. This was corroborated by PL, TCSPC, and EIS studies. Photogenerated electrons on the Pd NPs surface-activated hydrogen, enabling the hydrogenation of biomass derivatives at room temperature. Concurrently, photogenerated holes were consumed by IPA via O-H and C-H, leading to acetone formation. The optimized 1% Pd@N0.75CN catalyst exhibited exceptional activity in the hydrogenation of vanillin (VAN), achieving 79.6% conversion and 94.4% selectivity to vanillyl alcohol (VOL) within an hour. Moreover, reaction selectivity could be tuned by adjusting Pd NPs loading and reaction time, leading to complete VAN conversion and excellent selectivity (similar to 99%) to 2-methoxy-4-methylphenol (MMP) using 2% Pd@N0.75CN in 4.5 h. Comprehensive characterization and mechanistic studies provided insights into the structure-activity relationship, paving the way for the development of advanced NPs-based photocatalysts for challenging biomass valorization at ambient conditions.