钼催化剂结构对其催化气相丙烯环氧化反应选择性的影响

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。

Effects of structures of molybdenum catalysts on selectivity in gas-phase propylene oxidation

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 im‐pregnation and physical vapor deposition methods. The epoxidation activities of the prepared cata‐lysts showed direct correlations with their nanostructures, which were identified using transmis‐sion 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.