Reusable Nitrogen‐Doped Carbon‐Encapsulated Cobalt Catalyst for Efficient Stepwise Oxidation of Acetal‐Protected 5‐Hydroxy‐Methylfurfural to Furan‐2,5‐Dicarboxylic Acid

We report a ZIF‐67‐derived N‐doped carbon‐encapsulated cobalt catalyst (Co@N‐C) for the efficient, reusable, and noble metal‐free aerobic oxidation of concentrated aqueous 5‐hydroxymethylfurfural (HMF) derivatives in a stepwise fashion to furan‐2,5‐dicarboxylic acid (FDCA). Using acetal‐protected HMF with propane‐1,3‐diol (PD‐HMF) to suppress degradation at high substrate concentrations, Co@N‐C‐800p (Co‐containing ZIF‐67 pyrolyzed at 800 °C) delivers high yields in water while enabling effective PDO recovery. At 20 wt% PD‐HMF, a 96.8% yield of PD‐FFCA (acetal‐protected form of FFCA, 5‐formylfuran‐2‐carboxylic acid) was obtained at 99.2% conversion. Subsequent deprotection afforded FFCA and enabled recovery of propane‐1,3‐diol, after which FFCA was oxidized separately under the same conditions to FDCA in a 93.6% yield. Replacing soluble alkali carbonates with sparingly soluble Ca(OH) 2 provides buffered alkalinity that enhances formyl group oxidation, minimizes by‐products, and limits PDO loss at reduced base loadings. Radical scavenger experiments indicate a mechanism involving oxygen‐derived species that regenerate metallic Co sites via hydride removal. Although partial deactivation occurs through cobalt surface oxidation and CaCO 3 accumulation, full catalytic performance is restored by re‐pyrolysis. Overall, this work establishes Co@N‐C as an efficient, stable, and regenerable non‐noble metal catalyst for aerobic FDCA production at industrially relevant substrate concentrations.