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. (c) 2014 Elsevier Inc. All rights reserved.