Nanoparticles of the CeO2-ZrO2-La2O3 solid solution were prepared by the W/O microemulsion method. Ceria-zirconia-lanthana (Ce/Zr/La=1/1/0.06,mol) sample calcined at 1000 for 4h has higher surface area (126m2/g) and excellent thermal stability. Its particle size is 5-10nm. The presence of lanthana in the sample can improve obviously the thermal stability of the CeO2-ZrO2 solid solution.

Direct gas-phase epoxidation of propylene to propylene oxide (PO) by molecular oxygen was studied over the MoO3-modified supportedsilver catalyst. The effect of promoter and support on the performance of the Ag-MoO3 catalyst and their role were investigated by XPS, XRD, SEM, BET surface area, NH3-TPD, CO2-TPD techniques and so on. As the promoter, MoO3 plays a great role of electron- and structure-type bi-functional promoter. Of all the supports studied, ZrO2 is the most suitable one for the Ag-MoO3 catalyst. The presence of support can regulate the size of the Ag-MoO3 particles and the pore radii of catalyst, and decrease the loading of MoO3 from ∼50wt.% in the unsupported Ag-MoO3 catalyst to ∼4wt.% in the Ag-MoO3/ZrO2 catalyst. The properly weak Lewis acidic sites, the larger size of the Ag-MoO3 particles and pore channel on the Ag-MoO3/ZrO2 catalyst are beneficial to improve epoxidation performance of the catalyst. The effect of the reaction temperature and space velocity on the catalytic epoxidation of propylene was also investigated. The low temperature or high space velocity can decrease the deep oxidation of propylene oxide to improve the selectivity to PO. Over the 20%Ag-4%MoO3/ZrO2 catalyst at 400℃, 0.1MPa and space velocity of 7500h−1, the selectivity to PO of 60.3% was achieved with the O2 conversion of 4.8%; under the space velocity of 12 000h−1, the selectivity to PO was 71.5% with 2.5% O2 conversion.