Ethanol/acetaldehyde conversion into butadiene over sol–gel ZrO2–SiO2 catalysts doped with ZnO

Abstract

ZnO promoted ZrO₂–SiO₂ catalysts synthesized by a sol–gel method were investigated in the two-step ethanol transforming to 1,3-butadiene process. The influence of promoters and the preparation method of the catalysts on the catalytic performance were studied in detail and the reaction conditions were optimized. The as-prepared catalysts were characterized by BET, X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Fourier Transform Infrared Resonance (FT-IR), X-ray photoelectron spectroscopy (XPS), FT-IR spectroscopy of adsorbed pyridine (Py-IR) and temperature-programmed desorption of NH₃ (NH₃-TPD). ZnO added ZrO₂–SiO₂ catalysts show the best catalytic activity and the catalysts prepared by the hybrid sol–gel method were superior to those prepared by the sol–gel coupled with impregnation method. The addition of promoters in the ZrO₂–SiO₂ system decreased the total acidity and lowered the selectivity to dehydration products. The best performance with ethanol/acetaldehyde conversion of 40.7% and 1,3-butadiene selectivity of 83.3% was reached at 310 °C, ethanol/acetaldehyde mole ratio of 3.5 and WHSV of 1.4 h⁻¹ using a 0.5 wt% ZnO doped ZrO₂–SiO₂ catalyst.