Abstract
Cesium ion-exchanged ZSM-5 zeolites of high Si/Al ratios were found to exhibit distinct catalytic activity for selective dehydrochlorination of 1, 1, 2-trichloroethane(TCE) into 1, 1-dichloroethene(DCE) at 300-400°C. The zeolite ion-exchanged with CsOH exhibited very high activity in the first several pulses, but the activity decreased to a stationary level after repeated pulses. The activity lost in the initial pulses may be ascribed to CsOH supported on the zeolite, because extensive washing after ion-exchange, resulted in the stationary activity by the third pulse. It is noted that a high Si/Al ratio effects selective dehydrochlorination into DCE, indicating the special roles of silanol groups. Thus, Cs ions and their neighboring silanol groups appear essential for the induction of sufficient basicity for the stationary activity that is maintained by liberating hydrogen chloride during the elimination reaction. In contrast, CsOH is converted into CsCl on the zeolite; thus, losing its catalytic activity.
