Selective hydrogenation of furfural on Ru/Al-MIL-53: A comparative study on the effect of aromatic and aliphatic organic linkers

Two Al-MIL-53 materials containing aromatic and aliphatic linkers were prepared by using 1,4-benzenedicarboxylic acid (BDC) and adipic acid (ADP) as organic precursors, respectively. The resulting materials were characterized by BET, XRD, IR and TG. The characterization results indicated that the framework containing an aromatic ring (Al-MIL-53-BDC) shows a much higher surface area (761 m² g^-1) than the analogue with an aliphatic linker (Al-MIL-53-ADP, 4 m² g^-1). Al-MIL-53-BDC showed a larger adsorption capacity towards organic substrates such as furfural due to its higher surface area. Both materials can support Ru nanoparticles efficiently via a simple deposition-reduction method. XPS and TEM results suggested that Ru particles are predominantly oxidized with a particle size in the range of 1-4 nm. TPR results indicated that the oxidized Ru nanoparticles on Al-MIL-53-BDC can be reduced at around room temperature, forming metallic Ru nanoparticles which serve as the active sites for the catalytic hydrogenation of furfural under mild conditions. Full conversion of furfural and 100% selectivity to furfuryl alcohol can be achieved at 20 °C and 0.5 MPa H₂ on Ru/Al-MIL-53-BDC.