氢氟酸后处理对Silicalite-1催化环己酮肟气相Beckmann重排反应性能的影响

 研究了氢氟酸后处理对 silicalite-1 催化环己酮肟气相Beckmann重排反应性能的影响. 结果表明,经适当浓度的氢氟酸溶液处理后,催化剂的选择性和稳定性都明显改善. 其中, silicalite-1 原粉先经硝酸铵预处理后再进行氢氟酸后处理所得到的催化剂催化性能最好,反应53 h后环己酮肟的转化率仍保持在96%左右,己内酰胺的选择性高达96.1%. XRD, FT-IR和 29Si MAS NMR的结果表明,较高的具有氢键相互作用的硅羟基与孤立硅羟基的比例值对环己酮肟气相Beckmann重排反应有利,同时, silicalite-1 表面硅原子的排布方式对该反应也有重要影响.

Effect of Hydrofluoric Acid Post-Treatments on Catalytic Performance of Silicalite-1 for Vapor-Phase Beckmann Rearrangement of Cyclohexanone Oxime

This paper presents a novel modification of silicalite-1 with hydrofluoric acid treatment.Silicalite-1 treated with 0.04%HF solution exhibited remarkable improvements in stability and selectivity for Beckmann rearrangement of cyclohexanone oxime(CHO).Particularly,silicalite-1 catalyst with ammonium nitrate pre-treatment before HF modification showed the best catalytic performance: the conversion of CHO remained nearly 96% after 53 h reaction,and the selectivity for caprolactam during reaction was as high as 96.1%.XRD results showed that all samples hold the MFI structure after HF treatments,but the structural symmetry was changed from orthorhombic to monoclinic.FT-IR spectra revealed that the intensity of silanols,including isolated silanols and associated silanols on(silicalite-1) catalysts,decreased severely after HF modification,while the ratio of associated silanols to isolated silanols became much higher.These results indicate that a high ratio of associated silanols to isolated silanols is favorable to the Beckmann rearrangement reaction.However,a 0.45%HF solution used in the modification led to a decrease in activity and selectivity because the arrangement of silicon atoms was greatly changed,which was proved by~(29)Si MAS NMR.It is inferred that the arrangement of silicon atoms on the surface of(silicalite-1) is of significant importance to the catalytic performance of Beckmann rearrangement reaction.