Catalytic performance of metal-substituted ZSM-5 zeolites for vapor phase Bechmann rearrangement of cyclohexanone oxime

Abstract

Various MeZSM-5 (Me = B, Al, Fe, Ga) catalysts having different Si/Me ratios have been synthesized and characterized, and the vapor phase Beckmann rearrangement of cyclohexanone oxime to epsilon-caprolactam was undertaken using these catalysts. The results from NH3-TPD demonstrate that the metal substitution into the ZSM-5 framework produced weak or strong acid sites. The TPD profiles of AIZSM-5, FeZSM-5, and GaZSM-5 catalysts exhibited a broad range of weak and strong acid sites. On the other hand, the TPD profiles of BZSM-5 catalysts exhibited relatively small amounts of weak acid sites. The catalytic activities of the MeZSM-5 catalysts depended on the Si/Me ratio and the substituted metal type. The MeZSM-5 catalysts having high Si/Me ratios exhibited good catalytic performance. However, all the MeZSM-5 catalysts were rapidly deactivated with time on stream. In addition, the degree of deactivation with time was different for each substituted metal type. After reacting for 8 h, the order for the catalytic activities was AIZSM-5 > GaZSM-5 > BZSM-5 > FeZSM-5. These results are due to the acidities of the MeZSM-5 catalysts and the inherent characteristics of the substituted metal. The results from NH3-TPD and the catalytic reaction disclose that both weak and strong acid sites were not efficient for high catalytic performance in the MeZSM-5 catalyst system for vapor phase Beckmann rearrangement of cyclohexanone oxime.