Catalytic activity of the hydroxyl group produced by NO2 adsorption on Ca-exchanged zeolites

The enhancement of acid catalysis by the adsorption of nitrogen dioxide has been studied on the calcium ion-exchanged X-type zeolites of various degrees of the exchange. The enhancement is ascribed to the formation of the acidic hydroxyl group by the adsorption of nitrogen dioxide. As the ion-exchange degree increases, the formation of the hydroxyl group shows an optimum at 50 ~ 60%, but the catalytic activity for the isomerization of butenes continuously increases with steep acceleration at the exchange degree of 40 ~ 50%. The activity of an acidic hydroxyl group is strongly dependent on the number of calcium ion in the supercage of the zeolite. The formation of nitrate ion and nitrato complex observed by ir spectroscopy on the zeolite has been discussed in relation to the hydroxyl group formation.