In order to prepare suitable catalysts for the alkylation reaction of toluene with ethylene, ZSM-5 catalysts have been synthesized and modified by impregnation and/or ion exchange method with ammonium phosphate (P), magnesium acetate (Mg) or boric acid (B). The alkylation reaction was performed with these catalysts. Prepared ZSM-5 were characterized by XRD, IR, TPD and BET, which showed that these were confirmed as ZSM-5 zeolite. TPD experiments were performed to correlate acid sites with the activity and selectivity of modified ZSM-5 catalysts. ZSM-5 modified with P, Mg, and B increased p-selectivity with decreasing the activity. The catalyst containing 5 wt% phosphorus showed extremely low activity. ZSM-5 impregnated with 3 wt% phosphorus showed the largest yield among the ZSM-5's modified with different amounts of phosphorous. P-modified ZSM-5's were ion-exchanged with Mg to study the catalytic effect of Mg ion. All the catalysts were deactivated during the initial stage of the reaction. Activity remained fairly constant after about 2 hours. Modified ZSM-5 catalysts suppressed the formation of by products obtained from toluene dispropotionation even above 400℃. From the ammonia TPD results, the increase of p-selectivity and product selectivity could not be explained only by the decrease of the strength of the acid sites but explained by the effect of steric constraints. When thermal pretreatments were performed at 550℃-950℃, modified ZSM-5 catalysts were more sensitive to the thermal pretreatment than HZSM-5 catalyst. The pretreatment above 850℃ was not desirable because of the lower activity due to the severe disappearance of the acid site.
The reaction rate at 400℃ was proportional to the concentration of ethylene and independent of the concentration of toluene.
