Conversion of levulinic acid over rhenium oxide catalysts: Effect of metal content

The conversion of levulinic acid over rhenium oxide catalysts supported on ZrO2 and SiO2 in a batch reactor at 200 degrees C and 5 MPa of H-2 pressure was studied. The catalysts were prepared by incipient wetness impregnation with nominal loadings of 5-18 wt.%. The catalysts were characterized by N-2 physisorption, field emission scanning electron microscopy, X-ray diffraction, H-2-temperature programmed reduction, Fourier transform infrared spectroscopy of adsorbed pyridine, and X-ray photoelectron spectroscopy. The catalysts were highly active and selective to gamma-valerolactone. Catalytic activity, expressed as initial reaction rate and based on catalyst weight, was correlated with dispersion. The difference in the activity trend was attributed to ReOx-support interaction: ZrO2 interacted more strongly with ReOx and modified the electronic character of the sites, whereas SiO2 interacted weakly with ReOx, leading to unmodified Re active sites, irrespective of Re loading. All the catalysts exceeded 90 % selectivity to GVL.