Zirconium-lignin hybrid catalyst for the Meerwein-Ponndorf-Verley reduction of biomass-derived 5-hydroxymethylfurfural to 2,5-bis(hydroxymethyl)furan

The Meerwein-Ponndorf-Verley (MPV) reduction is an extremely attractive strategy for the selective hydrogenation of biomass-derived 5-hydroxymethylfurfural (HMF) to 2,5-bis(hydroxymethyl)furan (BHMF) in which constructing a low-cost and high-efficiency catalyst is very essential and crucial. In this work, the enzymatic hydrolysis lignin (EL), which is a waste residue in the production process of lignocellulosic ethanol, was firstly and directly adopted as the cheap organic ligand to prepare a new zirconium-lignin hybrid catalyst (Zr-EL) by a simple solvothermal self-assembly method. Amazingly, Zr-EL displayed superior catalytic activity for the MPV reduction of HMF to BHMF, providing 98.9% yield with a high turnover frequency (TOF) of 10.86 h^-1 in 2-propanol (iPrOH) at 140 °C for 4 h. Intensive characterization and analysis results indicated that this superior catalytic activity of Zr-EL was principally attributed to the cooperative effects of Lewis acid-base sites (Zr⁴⁺-O²⁻) under the assistance of good hydrophilicity. Additionally, Zr-EL showed excellent catalytic stability, and when it was recovered and reused for five successive reaction cycles, an apparent loss in the yield of BHMF was not observed. More meaningfully, Zr-EL also exhibited outstanding applicability, allowing it to convert various ketone and aldehyde compounds to the corresponding alcohol products with satisfactory yields in iPrOH via MPV reduction. Conclusively, this work presents a newfangled idea to utilize the low-rank biorefinery residues and construct more practical zirconium-based catalysts for the selective synthesis of high-value chemicals.