Cobalt single-atom and nano catalysts for efficient transfer hydrodeoxygenation of vanillin with formic acid

This study presents a Co catalyst with coexisting single-atoms and nanoparticles on N-doped carbon (Co₁+Co_n/N-C). Synthesized via a sacrificial MgO-template method, it achieves 100% vanillin conversion and >99% selectivity to 2-methoxy-4-methylphenol at 160°C using formic acid, outperforming single-component catalysts. Kinetic studies reveal a water-mediated dual hydrogen transfer pathway, lowering the apparent activation energy to 61.7 kJ/mol. Isotopic studies suggest a water-mediated mechanism, wherein water molecules facilitate proton transfer and hydrogen spillover through a hydrogen-bonding network. This process synergizes with formic acid dehydrogenation to enable a dual hydrogen transfer pathway, involving protonation of the aldehyde group and hydride (H⁻) attack. The catalyst maintains 95% conversion over ten cycles, demonstrating high stability for biomass upgrading.