P改性V-MCM-41催化剂的合成及其在丙烷直接脱氢中的应用

Phosphorous modified V-MCM-41 catalysts for propane dehydrogenation

钒基催化剂的脱氢性能与表面氧钒物种的形态密切相关。为了进一步增强传统原位合成的V-MCM-41催化剂上钒物种的分散性,本研究通过在制备过程中添加有机磷前驱物的方法对其进行改性。采用XRD、N_(2)吸附-脱附、TPR、TPD、XPS、拉曼光谱及O_(2)脉冲等方法对催化剂的结构、钒物种形态及分散度进行了系统的表征。表征结果表明,P改性后V-MCM-41催化剂的比表面积随着P含量的增加而缓慢下降,但整体仍能保持有序的六方介孔结构;P改性后表面钒物种的还原性和分散性均得到改善,聚合形态的钒物种比例明显下降。丙烷脱氢反应结果表明P改性后催化剂的丙烷脱氢性能和稳定性均有提高。在Si/P投料物质的量比为30时制备的催化剂能够获得最大表面钒氧位点和最佳丙烷脱氢性能。

The dehydrogenation performance of vanadyl catalysts was closely related to the form of surface vanadyl species.To enhance the vanadium dispersion,phosphorus was adopted to modify V-MCM-41 catalysts by using organic vanadium and phosphorus precursors.The influence of phosphorus introduction to the mesoporous structure and vanadyl species were investigated by various characterization techniques.The results showed that the catalysts could maintain ordered hexagonal mesoporous structures though the specific surface area slowly decreased along with the increase of phosphorus content.Both the reducibility and dispersion of the surface vanadyl species were improved.The proportion of polymerized vanadyl species obviously decreased due to the presence of phosphorus species.The propane dehydrogenation reaction results showed that both the catalytic performance and the catalyst stability were improved.Both the maximum surface vanadyl site density and optimum propane dehydrogenation performance were obtained over the sample with Si/P molar ratio of 30.