Selective Transfer Hydrogenation of Biomass-Based Furfural and 5-Hydroxymethylfurfural over Hydrotalcite-Derived Copper Catalysts Using Methanol as a Hydrogen Donor

A series of inexpensive copper-based catalysts, derived from hydrotalcite precursors, were screened for selective transfer hydrogenation of biomass-based furfural (FFR) to furfuryl alcohol (FA) and 2-methyl furan (MF), with methanol as both the solvent and a hydrogen donor. The specific textural characteristics of the prepared catalysts were characterized by various techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEm), thermogravimetric analysis/differential thermal analysis (TGA/DTA), nitrogen physisorption, temperature-programmed desorption in an ammonia atmosphere (NH3-TPD), temperature-programmed reduction in a hydrogen atmosphere (H-2-TPR), infrared (IR) spectra of pyridine adsorption, and X-ray photoelectron spectroscopy (XPS). The copper catalyst showed excellent transfer hydrogenation selectivity toward FFRto-FA transformation by giving a FA yield of 94.0 mol % at 473 K in methanol. Treating the copper catalyst with H-2/N-2 at 773 K led to the formation of a metallic Cu species in the activated sample. Interestingly, the resulting activated copper catalyst favored FFR-to-MF transformation by producing MF yield of 94.1 mol % at 513 K. The FFR-to-MF transformation involved a tandem reaction of FFR hydrogenation and successive FA hydrogenolysis; meanwhile, a synergistic effect between metallic Cu species and acidic sites on the catalyst surface played a key role in MF formation. In addition, the activated copper catalyst exhibited outstanding performance toward another biomass-related important conversion of 5-hydroxymethylfurfural (HMF) to 2,5dimethylfuran (DMF) with the desired DMF yield of 96.7 mol %. The recycling experiments revealed that both the copper and the activated copper catalysts maintained good activity and stability after five-time recycling. The research thus highlights a new perspective for a green, efficient, and biomass-related hydrogenation reaction using the readily available and inexpensive copper methanol catalytic system, while, without any external hydrogen supplies.