Ag-MoO3催化丙烯直接气相环氧化反应的原位红外研究

制备了对丙烯直接气相环氧化具有较好催化性能的Ag-MoO3催化剂, 采用原位FT-IR技术研究了丙烯、环氧丙烷及丙烯+氧气的混合气在Ag和Ag-MoO3催化剂表面上的吸附及反应行为. 研究表明, 丙烯在Ag和Ag-MoO3催化剂表面上吸附后, 均不发生化学反应, 而环氧丙烷吸附后在较高温度下则发生开环和聚合反应直至产生积炭. 与Ag催化剂相比, 在Ag-MoO3催化剂上, MoO3的加入在降低催化剂活性的同时, 在一定程度上抑制了产物环氧丙烷的开环及深度反应, 使环氧丙烷的选择性提高. 另外, 在较低的反应温度和较短的滞留时间下, 环氧丙烷发生深度反应的程度明显降低.

In situ FT-IR Study on the Direct Gas Phase Epoxidation of Propylene over Ag-MoO3 Catalyst

The Ag-MoO3 catalyst for direct gas phase epoxidation of propylene was prepared, and in situ FT-IR technology was used to study the adsorption and reaction behavior of propylene, propylene oxide(PO), and the gaseous mixture of propylene and oxygen on the surfaces of Ag and Ag-MoO3 catalysts. The results indicate that on using single Ag catalyst the selectivity to PO is very low, and Ag-MoO3 is an efficient catalyst for the direct epoxidation of propylene using molecular oxygen as oxidant. The studies of in situ FT-IR show that no chemical reaction occurs, within the range of the experimental temperatures, when propylene is adsorbed on the surface of Ag or Ag-MoO3 catalysts, whereas, the open-ring, polymerization, and coking of PO adsorbed on the Ag or Ag-MoO3 catalysts can occur at higher temperature. The presence of MoO3 in the Ag-MoO3 catalyst can inhibit the open-ring and deep reactions of PO to some extent, despite decreasing its activity, which leads to an increase in the selectivity of PO. The lower reaction temperature and shorter contact time are favorable to inhibit the deep reaction of PO on the surface of the catalyst.