Mn对异丁烯选择氧化制甲基丙烯醛Mo-Bi-Fe-Co-Cs-K复合氧化物催化剂的促进作用及其机理

Promotion Effect of Mn on the Mo-Bi-Fe-Co-Cs-K Composite Oxide Catalysts for Selective Oxidation of Isobutene to Methacrolein

采用共沉淀法制备了系列异丁烯选择氧化制甲基丙烯醛(MAL)Mo-Bi基复合氧化物催化剂,在常压固定床流动反应体系上考察了Mn助剂及其添加方式对催化剂性能的影响,并结合对相关催化剂物相结构的表征,探讨了Mn的作用机理.研究表明,以Mn(NO3)2为前驱体将Mn引入Mo-Bi-Fe-Co-Cs-K复合氧化物可显著提高催化剂的异丁烯转化率,催化剂活性的改善源于Mn加入后有助于生成更多Bi3FeMo2O12物相,但该物相的增多对催化剂MAL选择性的影响不大.以MnMoO4为前驱体引入Mn可以进一步改善催化剂的性能,在400℃,空气∶异丁烯=10∶1(体积比)和GHSV=2 000 mL.g-1.h-1的反应条件下,异丁烯的转化率可达92.8%,甲基丙烯醛的选择性最高可达93.5%,催化剂经72 h反应后性能稳定.XRD测试结果表明,以MnMoO4为前驱体引入Mn有助于促进催化剂上生成衍射峰位于25.6°和28.5°新物相,该物相的生成可大幅改善催化剂的选择性,进而显著提高催化剂在较高异丁烯转化率下的MAL得率.

Mn promoted Mo-Bi based composite oxide catalysts were prepared by coprecipitation method and were tested for selective oxidation of isobutene to methacrolein（MAL）.Catalytic reaction was carried out in a fixed-bed micro-reactor at atmospheric pressure.The surface area and structure of the catalysts were characterized by BET and XRD.It was found that addition of Mn（NO3）2 to Mo-Bi-Fe-Co-Cs-K composite oxide promotes the formation of Bi3FeMo2O12,which is favorable to enhance isobutene conversion of the catalyst.When Mn promoter was introduced to the Mo-Bi-Fe-Co-Cs-K composite oxide using MnMoO4 as precursor,both activity and selectivity of the catalyst can be significantly improved.Under the reaction conditions of 400 ℃ and GHSV=2 000 mL·g-1·h-1 using an air∶ isobutene=10∶ 1（volume ratio） mixture as reactant.Isobutene conversion of 92.8 % with MAL selectivity of 93.5% can be achieved.The performance of the catalyst remained stable after 72 h on stream.The results of XRD characterization indicated that the excellent performance of the catalyst was closely related to the formation of a new compound with XRD diffraction peaks at 25.6 at 28.5,which can significantly improve the selectivity of the catalyst especially at high isobutene conversion.