Enhanced Catalytic Transfer Hydrogenation of Biomass-Based Furfural into 2-Methylfuran over Multifunctional Cu-Re Bimetallic Catalysts

The synthesis of 2-methylfuran from biomass-based furfural is valuable in terms of addressing current environmental problems and energy crises. In this work, a series of Cu- A nd Cu-Re-based catalysts were prepared by the incipient wetness impregnation method and applied for the selective transfer hydrogenation of furfural to the fuel additive 2-methylfuran (2-MF) with the use of isopropanol as the hydrogen donor and solvent. The results showed that the 5Cu3Re/Al2O3 catalyst served as an effective multifunctional catalyst for the dehydrogenation, transfer hydrogenation, and hydrogenolysis reaction steps in the transfer hydrogenation process, exhibiting a 94.0% yield of 2-MF with a high selectivity after 4 h at 220 °C; additionally, this catalyst could be reused at least five times without an obvious drop in activity and the formation rate of 2-MF. The superior performance of the bimetallic CuRe/Al2O3 catalyst could be attributed to the synergy of the Al2O3 support, metallic Cu and Re species, in which Al2O3 with abundant acid-base sites and large specific surface area enabled the transfer hydrogenation process; the introduction of Cu on the Al2O3 surface enhanced the dehydrogenation of isopropanol and the hydrogenation of furfural into furfuryl alcohol, while the modification with Re species promoted the further hydrogenolysis of furfuryl alcohol into 2-MF. Moreover, the strong interaction of ReOx with Cu and Al2O3 resulted in the high stability of the bimetallic CuRe/Al2O3 catalyst. The present work provided an efficient and stable catalytic system for biomass-related hydrogenation reactions without any external hydrogen supply.