Selective hydrogenolysis of furfural into fuel-additive 2-methylfuran over a rhenium-promoted copper catalyst

Abstract

The effect of Re promoter on Cu/γ-Al₂O₃ catalysts with various Cu : Re molar ratios was comprehensively investigated in comparison to the monometallic Cu/γ-Al₂O₃ and Re/γ-Al₂O₃ catalysts. The combination of Re and Cu resulted in a difficulty in reduction behavior of the Cu species, as detected using hydrogen temperature-programmed reduction, indicating that the Re promoter had stronger metal–support interactions. The acidity, as confirmed by ammonia temperature-programmed desorption, increased with the Re loading. X-ray diffraction and X-ray absorption near edge structure measurements of the spent CuRe catalyst revealed the existence of metallic Cu, Cu₂O, CuO, amorphous CuAl₂O₄, ReO₃, and NH₄ReO₄. The as-synthesized catalysts without reduction were directly utilized for the hydrogenolysis of furfural (FAL) into the fuel additive 2-methylfuran (2-MF). The highest 2-MF yield (86.4%) was accompanied by a 10.4% 2-methyltetrahydrofuran (2-MTHF) yield using the optimal Cu₁Re_0.14 catalyst under the investigated conditions (200 °C, 6 h, and 20 bar H₂). The kinetic study using furfuryl alcohol (FOL), a primary intermediate, revealed that the rate of 2-MF production for the optimal Cu₁Re_0.14 catalyst was faster than that of the Cu benchmark. These results indicated that a small amount of oxophilic Re species could promote the hydrogenolysis of the C–OH bond in FOL to form 2-MF due to the synergistic effect between the Cu and Re active species. In addition, the activity of the Cu₁Re_0.14 catalyst remained highly stable through four consecutive experiments.