Silicalite-1的后处理对其催化环己酮肟气相Beckmann重排反应性能的影响

Effect of Post-treatment of Silicalite-1 on Its Catalytic Performance for Vapor-Phase Beckmann Rearrangement of Cyclohexanone Oxime

研究了silicalite 1分子筛的不同后处理方法对其催化环己酮肟Beckmann重排制己内酰胺性能的影响,这些方法包括水(或氨)蒸气处理以及在碱性、酸性或中性条件下用NH4NO3 处理.结合XRD ,FT IR和2 9SiMASNMR表征结果对silicalite 1催化剂的活性中心进行了探讨.结果表明,碱性条件下用NH4NO3 进行后处理对提高分子筛的催化性能最为有利.分子筛上无规则排布的末端硅羟基数量的减少。

Silicalite-1 was treated in various ways including steam treatment with water or ammonia, and treatment with ammonium nitrate aqueous solutions under acidic, neutral or basic conditions. Their catalytic performance for the vapor-phase Beckmann rearrangement were investigated. The silicalite-1 catalyst treated with ammonium nitrate under basic conditions exhibited the best catalytic performance. Its deactivation rate decreased when the reaction temperature increased from 350 degrees C to 370 degrees C. XRD results showed that all samples held their MFI structure after the post-treatments. FT-IR spectra revealed that there was not a clear correlation between the catalytic performance and the amount of silanol nests in catalysts, which have been considered to be the most favorable active sites for the vapor-phase Beckmann rearrangement. However, the vicinal silanol groups were correlated closely with the catalyst properties. Based on the results of FT-IR, it is proposed that the improvement of the catalytic activity of silicalite-1 treated with basic ammonium nitrate should be attributed to the decrease of terminal silanol with irregular arrangement and the appearance of hydrogen-bonded vicinal silanol. The results of Si-29 MAS NMR characterization also supported this conclusion.