Propylene Epoxidation On Copper-and Silver-based Catalysts With Molecular Oxygen As The Oxidant

Propylene oxide (PO) is an important chemical intermediate. At present, the industrial production of PO includes mainly Chlorohydrin process and Halcon process. The Chlorohydrin process produces large amount of wastewater, which results in serious equipment corrosion and environmental pollution. The Halcon process has the co-product problem. Propylene epoxidation with molecular oxygen as the oxidant is the most desirable reaction and is one of the most challenging topics in catalysis.In this thesis, series of modified silver and copper catalysts were prepared, and their catalytic performances on direct epoxidation of propylene with air as the oxidant were investigated. The active sites of the catalysts for the epoxidation were also discussed.NaCl or CuCl modified Ag catalysts were prepared. It is found that the addition of NaCl or CuCl in the catalysts could significantly enhance the PO selectivity. Under the optimized reaction conditions, 12.4% propylene conversion and 31.6% PO selectivity can be obtained on silver catalyst with 10wt% NaCl promotion.NaCl-Cu/Si02 catalysts were prepared and were found to be active and selective to propylene epoxidation. Under the reaction conditions, about 40% PO selectivity was obtained. It is very interesting to find that addition of hydrogen in the feedstock not only increases the PO selectivity but also keeps activity of the catalyst. A series of VCe1-xCux-NaCl catalysts with more stable Cu species were prepared. Under the optimum reaction conditions, about 70% PO selectivity was achieved. Characterization of the catalysts indicates that the Cu species is more stable in the VCe1-xCux-NaCl than those in the supported catalysts, and the reduced copper species with low valance might be the active sites.