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

The effect of Re promoter on Cu/gamma-Al2O3 catalysts with various Cu : Re molar ratios was comprehensively investigated in comparison to the monometallic Cu/gamma-Al2O3 and Re/gamma-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 Cu1Re0.14 catalyst under the investigated conditions (200 degrees C, 6 h, and 20 bar H-2). The kinetic study using furfuryl alcohol (FOL), a primary intermediate, revealed that the rate of 2-MF production for the optimal Cu1Re0.14 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 Cu1Re0.14 catalyst remained highly stable through four consecutive experiments.

Automated summary

The study investigated the effect of Re promoter on Cu/gamma-Al2O3 catalysts with different Cu: Re molar ratios, revealing that the combination of Re and Cu made the reduction behavior of Cu species difficult, while the acidity of the catalyst increased with higher Re loading. The optimal Cu1Re0.14 catalyst showed the highest 2-methylfuran yield in the hydrogenolysis of furfural, demonstrating faster production rates and stable activity over four consecutive experiments, indicating a synergistic effect between Cu and Re species in promoting the hydrogenolysis reaction.