Catalytic transfer hydrogenation of furfural to furfuryl alcohol and 2-methylfuran over CuFe catalysts: Ex situ observation of simultaneous structural phase transformation

Abstract

Low-cost CuFe catalysts with different calcination temperatures were synthesized by a facile citric acid complexation method. The formation of CuO and Fe2O3 with minor CuFe2O4 were observed after calcination at 600 °C and 700 °C, whereas the major phase of CuFe2O4 spinel-type structure was detected at 800 °C. To elucidate the structural CuFe transformation with catalytic transfer hydrogenation (CTH), the calcined catalysts were activated in situ into active species using isopropanol as the hydrogen donor, and their catalytic performances were simultaneously employed for the CTH of furfural to furfuryl alcohol and 2-methylfuran. Interestingly, the metallic Cu with minor Cu2O and magnetite Fe3O4 were generated after the CTH through combined XRD and ex situ XANES observations, acting as the active species for the reaction. The catalytic activity was higher for the CuFe600 and CuFe700 catalysts than for the CuFe800 catalyst because calcination at high temperature resulted in the formation of larger catalyst particles. Extended investigations on the catalyst lifetime confirmed that the deactivation of the CuFe700 catalyst was slower than that of the CuFe600 catalyst. Our investigation demonstrates the simultaneous catalyst activation and reaction accompanied by the catalyst recovery achieved by a magnetic field activated by isopropanol for the CuFe system.