Abstract:

A series of Cu/SiO₂ catalysts with 20.0% mass fraction of Cu loading was prepared by the ammonia evaporation method using SiO₂ as the support and Cu(NH₃)₄²⁺ aqueous solutions as the precursor. The catalysts were characterized through X-ray diffraction(XRD), H₂-temperaure programmed reduction(H₂-TPR), transmission electronic microscopy(TEM) and X-ray Auger spectra(XAES) to investigate the influence of the ammonia evaporation rate on the catalyst physical and chemical structure and its catalytic performance for the hydrogenation of dimethyl oxalate(DMO) to ethylene glycol(EG). The catalytic activity measurement experiments were performed under working conditions of 200 ℃, p=3.0 MPa, LHSV=0.4 h^-1 and the molar ratio of hydrogen to DMO(n(H₂):n(DMO)=80:1). The results indicate that the catalyst prepared under high vacuum during ammonia evaporation has better catalytic performance. For the catalyst prepared under ammonia evaporation pressure of 31.3 kPa, 99.9% conversion of DMO and 94.4% selectivity to EG are obtained. Characterizations through XRD, H₂-TPR, TEM and XAES suggest that the higher the ammonia evaporation rate, the faster and more uniform distribution of copper precursors upon the SiO₂ support, and the coagulation and growth of the Cu particles during calcination and reduction can be reduced, which guarantees the high catalytic activity, particularly the selectivity to EG.

Key words: ammonia evaporation pressure, Cu/SiO₂ catalysts, hydrogenation of dimethyl oxalate