High Catalytic Performance of MoO₃‐Bi₂SiO₅/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‐Bi2SiO5/SiO2 with Mo/Bi=5 calcined at 723 K, a propylene conversion of 21.99 % and a propylene oxide selectivity of 55.14 % were obtained at 0.15 MPa, 673 K, and flow rates of C3H6/O2/N2=1/4/20 cm3 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 723 K. The reaction mechanism of propylene epoxidation on MoO3‐Bi2SiO5/SiO2 catalysis is hypothesized to involve an allylic radical generated at the molybdenum oxide species and the activation of O2 at the bismuth oxide cations.

Direct Epoxidation of Propylene over Stabilized Cu+ Surface Sites on Titanium‐Modified Cu2O

“…[1] Thus,i dentifying appropriate catalysts for direct and selective epoxidation of propylene with molecular oxygen (C 3 H 6 + 1/2 O 2 !C 3 H 6 O) has received considerable attention. [2][3][4][5][6][7][8][9] Fore xample,A u nanoparticles supported on TiO 2 or titanium silicalite zeolites exhibit high selectivity (> 90 %) for PO. [4] However,t his approach requires co-feeding of large amount of H 2 and is limited by low conversion.…”

Effects of structures of molybdenum catalysts on selectivity in gas-phase propylene oxidation

“…Moreover, the PVD-prepared bismuth-molybdenum catalysts showed enhanced propylene conversion, but this did not lead to an improvement in the epoxidation activity. Although we previously reported the promoting effects of bismuth oxides on the epoxidation reactivity over molybdenum oxides [2], in our experiments the addition of bismuth to the molybdenum catalysts (introduced either by impregnation or by deposition of molybdenum and bismuth oxide nanoparticles close to each other, using PVD) improved only the formation of acrolein.…”

“…Acrolein is typically manufactured using a bismuth molybdate catalyst and air as the oxidizing agent; 90% propylene conversion and 85% selectivity for acrolein are achieved. Bis-muth-molybdenum catalysts for epoxidation reactivities have rarely been reported [2]. PO is usually produced industrially using either the chlorohydrin or Halcon process.…”

“…Supported bismuth-molybdenum mixed oxides showed high selectivity in propylene epoxidation, above 50%, using molecular oxygen as the oxidizing agent. The epoxidation reactivity over such catalysts is explained by the promoting effect of bismuth oxides on molybdenum oxide nanoparticles [2].…”

Direct Epoxidation of Propylene over Stabilized Cu+ Surface Sites on Titanium‐Modified Cu2O

“…Current industrial production of propylene oxide is mainly through the chlorohydrin process and hydroperoxide mediated process, which are neither cost effective nor environmentally friendly because of generating chlorinated or peroxycarboxylic waste 1. Thus, identifying appropriate catalysts for direct and selective epoxidation of propylene with molecular oxygen (C 3 H 6 +1/2 O 2 →C 3 H 6 O) has received considerable attention 2–9. For example, Au nanoparticles supported on TiO 2 or titanium silicalite zeolites exhibit high selectivity (>90 %) for PO 4.…”