Benzylation of benzene by benzyl chloride over Fe-, Zn-, Ga-and In-modified ZSM-5 type zeolite catalysts

Abstract

Liquid phase benzylation of benzene by benzyl chloride to diphenylmethane over H-ZSM-5, H-gallosilicate (MFI), H-galloaluminosilicate (MFI), H-ferrosilicate (MFI), H-ferroaluminosilicate (MFI), Fe₂O₃/H-ZSM-5, ZnO/H-ZSM-5, Ga₂O₃/H-ZSM-5 and In₂O₃/H-ZSM-5 zeolites (at 60 and 80°C) has been investigated. A complete or partial substitution of Al in H-ZSM-5 zeolite by Fe or Ga or an impregnation of the zeolite by Fe₂O₃, ZnO, Ga₂O₃ or In₂O₃ makes the zeolite highly active in the benzylation process. The redox function created due to the modification of the H-ZSM-5 zeolite by Fe, Zn, Ga or In seems to play very important role in the benzylation process. However, all these catalysts show a significant induction period for the reaction. The Ga₂O₃/H-ZSM-5 catalyst showed high benzene benzylation activity even in the presence of moisture in the catalyst and/or in the substrate. However, the reaction induction period is increased markedly with increasing the moisture and it is reduced by removing the moisture from the catalyst by refluxing with moisture-free benzene. It is also reduced by the HCl gas pretreatment to the catalyst before the benzylation reaction. The Ga₂O₃/H-ZSM-5 and In₂O₃/H-ZSM-5 catalysts showed excellent reusability in the benzene benzylation. Kinetics of the benzene benzylation (using an excess of benzene) over the H-GaMFI, H-GaAlMFI, H-FeMFI, Ga₂O₃/H-ZSM-5 and In₂O₃/H-ZSM-5 catalysts have also been thoroughly investigated. A plausible reaction mechanism for the reaction over the modified ZSM-5 zeolite catalysts is proposed.