Using solid acid catalysts to replace liquid acids in the liquid-phase Beckmann rearrangement of cyclohexanone oxime (CHO) into ɛ-caprolactam (CPL) is crucial for the environmentally friendly production of synthetic fibers, such as Nylon-6. In this work, we prepared aluminum-containing MCM-41 catalysts under ultrasonic irradiation with various Si/Al ratios for this purpose. Quantitative ¹H MAS NMR investigations show that ultrasonic irradiation significantly promotes the formation of active Brønsted acid sites (BAS) on the [Al]MCM-41 catalysts up to 8 times higher than those prepared at the same conditions without ultrasonic irradiation, and up to 12 times higher BAS density than those reported in the literatures. The catalytic performance of [Al]MCM-41 catalysts can be strongly improved with increasing the BAS density, particularly to the ratio of BAS/(weakly acidic SiOH groups). Moreover, [Al]MCM-41 catalysts dehydrated at 393 K obtained two time higher CHO conversion and CPL yield than that dehydrated at 473 K. Hydrogen-bonded water molecules retained at low dehydration temperature may block surface SiOH groups and promote the reaction process. With higher BAS density resulting from ultrasonic irradiation, [Al]MCM-41 catalyst (Si/Al = 10) in this work obtained the highest CPL yield among all [Al]MCM-41 materials reported for liquid-phase Beckmann rearrangement up to now. Finally, the reusability of [Al]MCM-41 catalyst was tested and no significant activity loss can be observed after five reaction cycles.

使用固体酸催化剂，以取代在环己酮肟（CHO）成液相贝克曼重排液体酸ɛ ε-己内酰胺（CPL）是环境友好的生产合成纤维，如尼龙-6的关键。在这项工作中，我们为此目的在超声辐射下以各种Si / Al比制备了含铝MCM-41催化剂。定量¹H MAS NMR研究表明，超声辐照可显着促进[Al] MCM-41催化剂上活性布朗斯台德酸位点（BAS）的形成，是在相同条件下未经超声辐照所制备的活性布朗斯台德酸位的高达8倍，最高是12倍。比文献中报道的更高的BAS密度。[Al] MCM-41催化剂的催化性能可以通过提高BAS密度，特别是提高BAS /（弱酸性SiOH基团）的比例来提高。此外，在393 K下脱水的[Al] MCM-41催化剂的CHO转化率和CPL产率是在473 K下脱水的两倍。在低脱水温度下保留的氢键水分子可能会阻塞表面的SiOH基团并促进反应过程。由于超声波辐照导致更高的BAS密度，在迄今为止报道的用于液相贝克曼重排的所有[Al] MCM-41材料中，这项工作中的[Al] MCM-41催化剂（Si / Al = 10）获得了最高的CPL收率。最后，测试了[Al] MCM-41催化剂的可重复使用性，在五个反应循环后未观察到明显的活性损失。