High catalytic performance of MoO3-Bi2SiO 5/SiO2 for the gas-phase epoxidation of propylene by molecular oxygen

Abstract

MoO3-Bi2SiO5/SiO2 catalysts with a Mo/Bi molar ratio of 5, prepared by a two-step hydrothermal and simple impregnation method, were investigated for the epoxidation of propylene by O2 and characterized by XRD, N2 absorption-desorption isotherms, thermogravimetric analysis (TGA), temperature-programmed reduction, NH3 temperature-programmed desorption (TPD), and IR, Raman, and X-ray photoelectron spectroscopy (XPS). On MoO3-Bi2SiO 5/SiO2 with Mo/Bi=5 calcined at 723K, a propylene conversion of 21.99 % and a propylene oxide selectivity of 55.14 % were obtained at 0.15MPa, 673K, and flow rates of C3H6/O 2/N2=1/4/20cm3 min-1. XRD, IR spectroscopy, and XPS results show that Bi2SiO5 and MoO3 are crystalline nanoparticles. NH3-TPD results indicate that the surface acid sites are necessary for the high catalytic activity. The results of TGA and N2 absorption-desorption isotherms reveal that a reasonable calcination temperature is 723K. The reaction mechanism of propylene epoxidation on MoO3-Bi2SiO 5/SiO2 catalysis is hypothesized to involve an allylic radical generated at the molybdenum oxide species and the activation of O 2 at the bismuth oxide cations. A new sensation in epoxidation: We describe the probable synergistic effects of MoO3 and Bi 2SiO5 in propylene epoxidation. The reactive centers consist of nanoparticulate species of crystalline MoO3 to activate the propylene and bismuth oxide cluster cations to activate O2. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.