Aerobic oxidation of 5-hydroxymethylfurfural to 2,5-difurancarboxylic acid over Pd-Au nanoparticles supported on Mg-Al hydrotalcite

Abstract

A series of reconstructed hydrotalcite supported monometallic Au or Pd and bimetallic Pd-Au nanoparticles with various Pd/Au ratios were synthesized. The physicochemical properties of these catalysts were charaterized by X-ray diffraction (XRD), X-ray photoelectronic spectroscopy (XPS), Transimission electron microscopy, N2 adsorption, etc. The catalysts were used for the aerobic oxidaiton of 5-hydroxymethylfurfural(HMF) into 2,5-furandicarboxylic acid (FDCA) in an alkaline aqueous solution. The monometallic Pd or Au catalyst could not oxidize the intermediate product-5-hydroxymethyl-2-furanic acid (HMFCA), while bimetallic Pd-Au catalysts exhibited good performances for HMFCA oxidation. A high yield of FDCA up to 90% was achieved over the Pd-Au/HT catalyst with the Au/Pd ratio of 4 at 60 °C for 6 h. The enhanced oxidation activity of HMF for the bimetallic catalysts is attributed to the syneretic effect between Au and Pd nanoparticles and the formation of smaller particle size that facilicates the oxidation of HMF to FDCA. The Pd-Au/HT(1 :4) catalyst also exhibited a good stabiblity without significant loss in FDCA yield after five succesive cycles.