摘要
Molybdenum-based catalysts for the gas-phase oxidation of propylene with air were investigated. Various types of silica-supported molybdenum oxide and molybdenum-bismuth mixed oxide cata- lysts were prepared from inorganic and organometallic molybdenum precursors using wet impregnation and physical vapor deposition methods. The epoxidation activities of the prepared cata- lysts showed direct correlations with their nanostructures, which were identified using transmission electron microscopy. The appearance of a partly or fully crystalline molybdenum oxide phase, which interacted poorly with the silica support, decreased the selectivity for propylene oxide for- mation to below 10%; non-crystalline octahedrally coordinated molybdenum species anchored on the support gave propylene oxide formations greater than 55%, with 11% propylene conversion. Electrochemical characterization of molybdenum oxides with various morphologies showed the importance of structural defects. Direct promotion by bismuth of the epoxidation reactivities over molybdenum oxides is disputed.
考察了Mo基催化剂上空气气相氧化丙烯反应.从无机的和有机金属Mo前驱体出发,采用浸渍法和物理气相沉积法(PVD)制备了不同类型的SiO2负载氧化钼和Mo-Bi复合氧化物催化剂.透射电镜结果证实,所制催化剂上环氧化反应活性与其纳米结构直接有关.催化剂中出现部分或完全结晶的氧化钼相,它们与载体SiO2的相互作用较弱,使得反应生成环氧丙烷的选择性低于10%,而锚合在SiO2上的非结晶的八配位Mo物种上的环氧丙烷选择性达55%以上,此时丙烯转化率约为11%.不同形貌氧化钼的电化学表征结果证实了结构缺陷的重要性.另外,还讨论了Bi对氧化钼催化环氧化活性的直接促进效应.
基金
A support by VEGA grant 2/0129/13 is acknowledged by I.V.
