Shape and ligand effect of palladium nanocrystals on furan hydrogenation

Abstract

The Pd nanocrystals, including cubes, octahedra and wire, were prepared by shape-controlled solution phase reduction. The shape-dependent effect of Pd, and the effect of residual halogen ions and PVP, were investigated in selective hydrogenation of furan to tetrahydrofuran (THF). It was found that the residual halogen ions and PVP on the surface of Pd nanocrystals possibly reduced the hydrogenation activity and in turn it prevented the further reaction such as ring opening, so high selectivity towards THF was achieved even at high temperature. The 5-fold twinned wire displayed poor activity in furan hydrogenation due to a large amount of strongly adsorbed iodide ion residues covering most of the Pd active sites. An appropriate PVP residue is necessary, which can effectively maintain the shape and size stability of the Pd nanocube and octahedron, although the residual PVP partially blocks active Pd sites and reduces the activity for furan hydrogenation. The Pd nanocube enclosed by {100} facets exhibited about two times higher turnover frequency and lower apparent activation energy compared to the octahedron enclosed by {111} facets, suggesting a significant shape-dependent effect.