Highly Selective Conversion of HMF to 1-hydroxy-2,5-hexanedione on Pd/MIL-101(Cr)

Saturated cyclohexene water was used as the reductant for the preparation of Pd/MIL-101(Cr). The catalysts were characterized by XRD, N-2 adsorption/desorption isotherms, XPS, TEM, FTIR, ICP-AES and in-situ FTIR spectra of adsorbed pyridine. The water saturated by cyclohexene was proved to be an effective reductant to produce metallic Pd catalyst. The texture of MIL-101(Cr) was kept well after the introduction of Pd to MIL-101(Cr). The hydrogenation of HMF to 1-hydroxy-2,5-hexanedione (HHD) was conducted in water using Pd/MIL-101(Cr) as catalyst. After reacted for 6 h at 413 K 4 MPa H-2, up to 82% yield of HHD was achieved without acid additives. The MIL-101(Cr) acted both as support and acid catalyst generated from the open Cr3+. The stability of the catalyst was investigated to find that the TOFs decreased slightly after the catalyst was used. The decline in the catalytic activity was discussed and ascribed to the condensation of intermediates on the active sites and the partly aggregate of Pd.