Carbon supported Pd–Cu catalysts for highly selective rearrangement of furfural to cyclopentanone

The aqueous phase hydrogenation of furfural to cyclopentanone was investigated using carbon supported Pd–Cu catalysts prepared by various methods. The most active and selective Pd–Cu catalysts were obtained using electroless plating procedure of deposition of copper in the presence of tartrate carboxylate ligands. It is an alternative and promising way to deposit metal nanoparticles onto the surfaces of porous solid supports. As the XRD data revealed in these catalysts beside metallic palladium with the particle sizes 6.8 nm the copper exist mainly in Cu+ oxidation state as Cu2O and the metallic copper is practically absent. The selectivity to cyclopentanone was enhanced gradually by the addition of 3, 5 and 10 wt% of copper precursor on the pre-reduced 5%Pd/C catalyst. An appropriate Pd0 and Cu+ distribution is presumed to be a key in gaining excellent catalytic activity. Under reaction conditions where mass-transfer effects were eliminated the furfural conversion about 98% and cyclopentanone yield 92.1 mol% were achieved using only 1 wt% concentration of 5%Pd–10%Cu/C catalyst and reaction time 1 h. According to the proposed mechanism the dominant parameters responsible for reaching very high selectivity of cyclopentanone are (i) very high yield of primary formed furfuryl alcohol and (ii) higher rate of its subsequent conversion to cyclopentanone via the pathway not involving 4-hydroxy-2-cyclopentenone as the main intermediate.