磷钼钒酸催化甲基丙烯醛氧化反应机制及过程研究

围绕甲基丙烯醛选择性氧化制甲基丙烯酸的反应过程，利用原位红外分析装置研究了甲基丙烯醛在磷钼钒酸催化剂上的原位吸附和反应过程，发现了甲基丙烯醛在杂多酸催化剂桥氧键吸附产生的中间结构，并提出了该催化过程的反应机理。进一步获得了不同温度下反应过程的中间状态，发现钒氧物种由一级结构迁移至二级结构能有效提高催化性能。优化了催化剂预还原温度，250℃下还原3 h后催化剂活性最高。

Study on mechanism and process of oxidation of methacrolein catalyzed by phosphomolybdovanadic acid

As an important chemical raw material, methacrylic acid (MAA) is often used in the production of coatings, adhesives, ion exchange resins, etc. Among the production routes of MAA, the oxidation route of isobutene is a research hotspot. In this route, the first step is to produce methacrolein (MAL) by oxidation of isobutene, and then to produce MAA by catalytic oxidation of MAL with heteropoly acid catalyst. Keggin type heteropoly acid catalyst has been successfully applied in this route. In this work, phosphomolybdovanadic acid was took as an example to analyze the adsorption and reaction process of MAL on heteropoly acid catalyst. The results of in-situ FT-IR showed that the ester intermediate adsorbed on the bridging oxygen of heteropoly acid catalyst was important. After MAL adsorption, the ester intermediate was formed and further oxidized to carboxyl intermediate or carbon oxides. The mechanism of catalytic oxidation of MAL over heteropolyacid catalysts was further proposed based on the above conclusions. The reaction process was analyzed at different temperatures. The characteristic peak of vanadium oxide compound in the secondary structure of the catalyst was observed when the reaction temperature rose to 310℃, and the peak was enhanced with the increase of temperature. Referring the results of catalyst evaluation, the conversion of the reaction increased significantly when the vanadium oxide compound transferred to the second structure, indicating that it was the active site in the reaction. It was considered that the migration of vanadium oxide compound from primary structure to secondary structure was the key reason for the significant improvement of catalytic performance. By reduction with H2, the migration of vanadium oxide compound was promoted, and the conversion of MAL and the yield of MAA were further improved. After reduction at 250℃ for 3 h, the catalyst had the highest activity, and the yield of MAA increased from 17.3% to 27.2%.