Beckmann rearrangement of cyclohexanone oxime over Al-MCM-41 and P modified Al-MCM-41 molecular sieves

P modified Al-MCM-41 molecular sieves were prepared via impregnating method and applied to vapor-phase Beckmann rearrangement reaction. The catalysts were characterized by XRD, N-2 adsorption, ICP-OES, NH3-TPD and Al-27 and P-31 MAS NMR spectroscopy. NH3-TPD results reveal that P modification of Al-MCM-41 can increase the number as well as the strength of weak acid sites, whereas the introduction of P decreases the number of intermediate acid sites. Al-27 and P-31 MAS NMR results indicate that formation of Si-O-P-O-Al seems to be favored in P modified Al-MCM-41 catalysts. Overall, these results indicate that P modified Al-MCM-41 catalysts can improve their selectivity for caprolactam. In addition, more abound weak acid sites with certain acid strength are favorable to Beckmann rearrangement. (C) 2010 Elsevier B.V. All rights reserved.