IR and TPD (temperature-programmed desorption) studies of carbon dioxide on basic site active for 1-butene isomerization on alkali-added zeolite X

Abstract The basic zeolites X which contain alkalis (K, Rb, Cs) in excess of the ion-exchange capacity (alkali-added zeolite X) showed an activity for 1-butene isomerization at 273 K, whereas alkali ion-exchanged zeolite X showed almost no such activity. The activities of the different alkali-added zeolites were in the following order: Cs-added zeolite X > Rb-added zeolite X > K-added zeolite X ≫ Na-added zeolite X. Temperature-programmed desorption (TPD) of adsorbed CO 2 showed that the amounts of adsorbed CO 2 were several times larger for alkali-added zeolites X than for alkali ion-exchanged zeolites X. The poisoning experiment with CO 2 indicated that the active sites of alkali-added zeolites X are so basic that they retain CO 2 against evacuation at 573 K. The state of CO 2 adsorbed on the active sites was identified to be bidentate carbonate by IR study.