Enhanced catalytic performance in the gas-phase epoxidation of propylene over Ti-modified MoO3–Bi2SiO5/SiO2 catalysts

• The Ti-modified catalysts exhibited high activity and stability for propylene epoxidation.
• The formation of propylene oxide could be promoted by the highly dispersed MoO3.
• The formation of Bi2Mo3O12 could be prevented after the modification of MoO3–Bi2SiO5/SiO2 by Ti.
• The decrease of the reactivity of lattice oxygen and the strong acidity are favor to PO formation.
• Significant synergistic effects were found between MoO3, bismuth oxide clusters and Ti species.

It was found that Ti-modified MoO3–Bi2SiO5/SiO2 exhibited excellent catalytic performance for the epoxidation of propylene by molecular oxygen. The effect of Ti on the performance of the catalysts was investigated, and the results showed that the high surface area, greater pore size, and moderate acidity of the Ti-modified catalyst were favorable to the selective formation of propylene oxide (PO). Interactions between MoO3, bismuth oxide clusters, and Ti species were proposed to favor PO formation. The presence of Ti not only enhanced the dispersion of MoO3 nanoparticles but also inhibited the reactivity of the lattice oxygen and reduced the strong acidity of the catalyst, contributing to the increase in C3H6 conversion and PO selectivity, respectively. Kinetic studies indicated that a high space velocity or low reaction temperature was beneficial for improving the selectivity to PO by decreasing the deep oxidation of PO.

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