用原位红外技术研究Ag-MoO_3/ZrO_2催化丙烯气相环氧化反应

Study on the Direct Gas Phase Epoxidation of Propylene over Ag-MoO_3/ZrO_2 Catalyst by in situ FT-IR

制备了对丙烯直接气相环氧化具有优良催化性能的Ag-MoO3/ZrO2催化剂,采用原位FT-IR技术研究了丙烯、环氧丙烷及丙烯和氧气混合气在载体和催化剂上的吸附及反应行为.研究表明,丙烯在ZrO2载体和20%Ag-4%MoO3/ZrO2催化剂上吸附后,均不发生化学反应,而环氧丙烷在ZrO2载体上吸附后于400℃发生开环反应,在20%Ag-4%MoO3/ZrO2催化剂上吸附后于300℃发生开环反应.当丙烯和氧气混合气在ZrO2载体上共吸附后,随着反应温度从室温升高至400℃,二者开始反应生成CO2和H2O;混合气在20%Ag-4%MoO3/ZrO2催化剂上共吸附后于350℃开始反应.对比非负载型Ag-MoO3催化剂的研究结果可见,ZrO2载体的存在使催化剂的活性下降的同时,提高了对产物环氧丙烷的选择性.

The Ag-MoO3/ZrO2 catalyst for the direct gas phase epoxidation of propylene was prepared. The in situ FT-IR technology was employed to study the adsorption and reaction behavior of propylene, propylene oxide （PO） and the mixture gas of propylene and oxygen on the surface of ZrO2 support and Ag-MoO3/ZrO2 catalyst. The studies show that propylene adsorbed on ZrO2 support or 20%Ag-4%MoO3/ZrO2 catalyst is stable. When the reaction temperature is more than 400 ℃, the ring-opening reaction of propylene oxide adsorbed on ZrO2 support happens; over the 20%Ag-4%MoO3/ZrO2 catalyst, the ring-opening reaction of adsorbed propylene oxide occurs at 300 ℃. As the reaction temperature rises to 400 ℃, propylene adsorbed reacts with oxygen adsorbed on ZrO2 support to form water and CO2; over the 20%Ag-4%MoO3/ZrO2 catalyst, this surface reaction just takes place at 350 ℃. Comparing with the unsupported Ag-MoO3 catalyst, the presence of ZrO2 support can increase the selectivity of PO and while decrease the conversion of propylene.