Mechanistic insights into copper oxides catalyzed bio-based furfural hydrogenation using methanol as in-situ hydrogen donor

In the present study, CuO and Cu2O were employed in H-transfer transformation of bio-based furfural (FFR) using methanol as both the solvent and an in-situ hydrogen source, to clearly elucidate the catalytic mechanism of copper oxides (CuOx, x = 0.5, 1) during the reaction. A number of characterization techniques including XPS, H2-TPD, in-situ FTIR, etc., were undertaken to track the state of copper species. Owing to the synergistic effect of in-situ generated H2, Cu0 species and CuOx derived Brønsted/Lewis acid sites, FFR could be efficiently hydrogenated into FA and subsequently deoxygenated into MF in methanol. The combined results from in-situ characterizations and experiments show that the FFR-to-FA (FA, furfuryl alcohol) and FFR-to-MF (MF, 2-methylfuran) conversions largely depended on the hydrogen production capability from methanol reforming and FFR adsorption strength over CuOx. Density functional theory (DFT) calculations demonstrated that the CuO(200) surface revealed lower free energy and energy barriers for methanol reforming and FFR transfer hydrogenation. This study provides a promising guidance for reasonably designing copper-based materials in the hydro-upgrading of bio-based unsaturated molecules into value-added chemicals in methanol without external H2 supply.