Study on Ag-Mo catalyst for direct vapor-phase epoxidation of propylene by molecular oxygen

Propylene oxide (PO) is a key intermediate for polymer and organic synthesis. For the economic and environmental reasons, a mainstream strategy being considered is to develop a direct vapor-phase epoxidation of propylene to PO using molecular oxygen as oxidant. In this paper, a series of supported catalysts using Ag, MoO3 as active component were prepared by using impregnation and sol-gel methods, and the effects of promoters and supports on the performance of the catalysts were investigated. The unit of micro-reactor and on-line gas chromatography was used to investigate the catalytic performance of the catalysts. The results showed that the supports and promoters have great influence on the performance of the catalysts. Among all the catalysts, NaCl-Ag-MoO3-CsNO3/TiO2-ZrO2 catalyst, prepared by impregnation, gives the best catalytic performance in epoxidation of propylene without any gaseous additive, the conversion of oxygen and selectivity for PO are 11.0% and 34.8% at 400degreesC respectively, and are 33.0% and 35.3% at 450degreesC respectively. The excellent performance of this catalyst comes probably from the cooperation of Na+ and Cs+ to the silver active site, because Na+ and Cs+ can counteract the negative charges on the surface of catalyst to a certain extent, which inhibits the adsorption of allyl hydrogen and is in favor of the adsorption of olefin carbons. Meanwhile, it was found that the MoO3/SiO2 catalyst prepared by sol-gel method has higher catalytic activity for the title reaction.