Disproportionation of Toluene by Modified ZSM-5 Zeolite Catalysts with High Shape-selectivity Prepared Using Chemical Liquid Deposition with Tetraethyl Orthosilicate

Shape-selective catalysts for the disproportionation of toluene were prepared by the modification of the cylinder-shaped ZSM-5 zeolite extrudates with chemical liquid deposition with TEOS (tetraethyl orthosilicate). Various parameters for preparing catalysts were changed to investigate the suitable conditions. The resulting catalysts were tested in a pressured fixed bed reactor and characterized by SEM (scanning electron microscopy). The conversion of toluene and para-xylene selectivity were influenced remarkably by the n(SiO2)/n(Al2O3) ratio of ZSM-5 zeolite, the type and amount of deposition agent, acid and solvent used, and the time and cycle of deposition treatment. TEOS was proved to be a more efficient agent than the conventional polysiloxanes when the deposition amount was low. The catalyst prepared at the suitable conditions exhibited a high para-xylene selectivity of 91.1% with considerable high conversion of 25.6%. SEM analyses confirmed the formation of a layer of amorphous silica on the external surface of ZSM-5 zeolie crystals, which was responsible for the highly enhanced shape-selectivity.