Promotional effect of Y 2O 3 on the performance of Ag/α-Al 2O 3 catalyst for epoxidation of propylene with molecular oxygen

Abstract

The Ag/α-Al 2O 3 catalysts modified with rare earth, alkali and alkaline earth metal oxides for the epoxidation of propylene by molecular oxygen were prepared and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), CO 2-temperature programmed desorption (CO 2-TPD), BET surface area and pore diameter distribution. The results show that the appropriate pore diameter and high surface area of α-Al 2O 3 support, and the suitable basic sites on the surface of catalyst are necessary to the highly effective Ag catalyst for the epoxidation of propylene. The presence of a small quantity of Y 2O 3 can restrain the sintering of Ag particles on the surface of α-Al 2O 3 and adjust the surface basicity of catalyst. The loadings of promoters and reaction temperature obviously affect the performance of Ag catalysts. Under the reaction condition of 0.1 MPa, 245 °C, space velocity 2000 h −1 and the feed of 20% C 3H 6/8% O 2/N 2, 4% conversion of propylene and 46.8% selectivity to propylene oxide were obtained over the 20 wt% Ag–0.1% Y 2O 3–0.1% K 2O/α-Al 2O 3 catalyst.