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.