Characterization of active sites working on FSM-16 during the vapor-phase Beckmann rearrangement of cyclohexanone oxime Original Research Article

The behaviors of ε-caprolactam, cyclohexanone oxime and Beckmann rearrangement by-products on FSM-16 and Al2O3/FSM-16 have been investigated in detail by means of TPD and reactions in the presence of organic acids and pyridine. The TPD spectra on FSM-16 of ε-caprolactam, cyclohexanone oxime, Beckmann rearrangement by-products and mixtures of by-products can be explained by postulating that there are four kinds of active sites, i.e. two kinds of nitrile formation sites (Sites A and R), a cyclohexanone formation site (Site B) and a nitrile adsorption site (Site α). The TPDs of cyclohexanone oxime adsorbed on Al2O3/FSM-16 in the presence and absence of water vapor suggest that the presence of water accelerates the formation of cyclohexanone on Site B. Addition of acetic acid suppresses conversion of ε-caprolactam to nitriles, and that addition of pyridine has no effect on the TPD spectrum. Addition of acetic acid to the reactant during the Beckmann rearrangement on Al2O3/FSM-16 improved the ε-caprolactam yield and catalyst’s life.