用原位红外技术研究Ag-MoO3/ZrO2催化丙烯气相环氧化反应

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.

Study on the Direct Gas Phase Epoxidation of Propylene over Ag-MoO3/ZrO2 Catalyst by in situ FT-IR

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.