通过浸渍法制备了6种Na盐修饰的Cu/SiO₂催化剂,利用XRD、TEM和XPS对其晶相结构、粒径大小和Cu物种价态进行了分析,考察了Na盐促进剂种类和摩尔分数对Cu/SiO₂催化剂上丙烯氧气环氧化反应性能的影响。结果表明,6种Na盐可以不同程度地还原Cu²⁺物种,生成不同含量的Cu⁰或Cu⁺物种。6种Na盐都可以提高Cu/SiO₂的丙烯环氧化活性,而且Na₂CO₃最有利于环氧丙烷的生成。适量的Na₂CO₃可以促进Cu⁺物种的形成,有利于丙烯环氧化反应的进行,但过量的Na₂CO₃会导致Cu⁰物种的产生以及Cu物种的聚集,反而不利于环氧丙烷的生成。Cu⁺物种摩尔分数越高,Cu/SiO₂的丙烯环氧化活性和环氧丙烷的形成速率也越大。小粒径的Cu⁺物种具有最高的丙烯环氧化活性,是丙烯氧气环氧化反应的活性中心。

Cu/SiO₂ catalysts modified with six kinds of Na salts respectively are synthesized through an incipient wetness impregnation method,and their crystalline phase,particle size and Cu species valence state are characterized by means of XRD,TEM and XPS.The influences of the variety and mole fraction of Na salts on the activity of Cu/SiO₂ catalysts in propylene epoxidation is investigated in detail.It is found that Cu²⁺ species may be reduced to varying degrees by six kinds of Na salts,which can produce different amount of Cu⁰ species or Cu⁺ species.All these six kinds of Na salts can improve the activity of Cu/SiO₂ for propylene epoxidation,and Na₂CO₃ is the most favorable for the formation of propylene oxide.The appropriate amount of Na₂CO₃ is able to promote the formation of Cu⁺ species and facilitate the epoxidation of propylene,but too much amount of Na₂CO₃ results in the generation of Cu⁰ species and the aggregation of Cu species,which is not conducive to the formation of propylene oxide.The higher the Cu⁺ species mole fraction,the higher the activity of Cu/SiO₂ in propylene epoxidation and the higher the formation rate of propylene oxide.Cu⁺ species with small size have the most activity for propylene epoxidation and are the main active sites for propylene epoxidation reaction.

马应圆(2000-),女,本科生,研究方向为多相催化反应,18809606002@qq.com;苏暐光(1981-),男,博士,副研究员,研究方向为新型催化剂与催化反应,通讯联系人,weiguangsu@nxu.edu.cn。