Pd-Decorated Magnetic Spinels for Selective Catalytic Reduction of Furfural: Interplay of a Framework-Substituted Transition Metal and Solvent in Selective Reduction

The reduction of functional platform chemicals, such as furfural, to industrially important chemicals and fuel requires precise modulation of surface reactivity of the catalyst to obtain the desired reactivity and selectivity. In this study, the selective reduction of furfural (FAL) to furfuryl alcohol (FOL) and tetrahydrofufuryl alcohol (THFA) is achieved by the transition metal interplay in the framework structure of magnetic spinels Fe3O4 and by modulating the reaction medium. Herein, FAL is selectively and quantitatively reduced to FOL in water at very mild reaction conditions over Pd-decorated CuFe2O4, whereas FAL is selectively converted to THFA in hexane at mild reaction conditions over Pd-decorated NiFe2O4, using H2 as an economical reducing agent. The Pd loading, reaction temperature, H2 pressure, and reaction time are minimized to obtain the best selectivity toward THFA. Different modes of FAL adsorption occur on CuFe2O4 and NiFe2O4 surfaces. Dissociative adsorption of H2 occurs on Pd sites to form Pd-H species, followed by transfer hydrogenation from Pd-H to FAL adsorbed on spinels, leading to the formation of FOL or THFA. Efficient magnetic recyclability and the hot filtration test show that the catalyst exhibits no significant loss in the activity even after five recycles. Catalysts exhibit very high activity, selectivity, and low activation energy, which are very attractive for academic and industrial points of view.