Background2,2,6,6-tetramethylpiperidin-oxyl (TEMPO) accompanied with Cu has been validated as a promising oxidative catalytic process for oxidizing 5-hydroxymethylfurfural (HMF) to value-added products. Since Cu-O cluster plays an important role in TEMPO-based HMF oxidation, and N-O moiety would facilitate the catalytic cycle of TEMPO regeneration, an interesting solid-phase material, copper nitrate hydroxide (CNH) (Cu2(OH)3NO3) is proposed for the first time for co-catalyzing TEMPO to oxidize HMF into a valuable product, 2,5-diformylfuran (DFF). MethodsIn particular, a CNH with a 2D elliptical and porous surface is fabricated to become the leaf-like porous CNH (LPCNH) to maximize surface contact via a relatively simple procedure, and LPCNH would be an advantageous catalyst with TEMPO for converting HMF into DFF. Significant findingsWhile TEMPO or LPCNH was unable to oxidize HMF into DFF, the combination of LPCNH/TEMPO rapidly, and efficiently converted HMF to DFF with high selectivities. At 140 °C, a significantly high YDFF = 99.3% with SDFF = 100% can be obtained, and surpass almost all reported values, indicating that LPCNH+TEMPO is advantageous and selective to convert HMF into DFF. LPCNH could be also reusable for co-catalyzing with TEMPO for converting HMF to DFF. These findings validate that LPCNH is certainly a useful heterogeneous catalyst for valorizing HMF.