2-dimensional nanoleaf-like porous copper nitrate hydroxide as an effective heterogeneous catalyst for selective oxidation of hydroxymethylfurfural to diformylfuran

Background: 2,2,6,6-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). Methods: In 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 findings: While 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 Y_DFF = 99.3% with S_DFF = 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.