Dealumination of ZSM-5 Zeolites by Steaming

Abstract

Dealumination of ZSM-5 type zeolite (SiO2/Al2O3=66~680) framework by steaming was investigated by 27A1-MAS NMR and FT-IR. Steaming was carried out using an atmospheric pressure flow system at 773~873 K in a stream of 100% steam. The rate of dealumination showed a second-order dependency on the concentration of framework aluminum as shown in Figs. 2 and 4. These results suggest that the dealumination via the hydrolysis of a Si-O-Al bond may be catalyzed by acid(H+) which freely move in the pore of the zeolite. Effect of alkali or alkaline earth metal ions(M) on the dealumination of zeolite (SiO2/Al2O3 = 66) framework was investigated. The analytical data of the ion-exchanged zeolites are summarized in Table 1. Under the steaming conditions at 873 K for 13. 5 h, the dealumination quantities of alkali or alkaline earth metal ions exchanged zeolite framework were inversely proportional to the concentration of the exchanged cations, and did not depend upon the kind of the alkali or alkaline earth metal ion (Fig. 6). Consequently, the dealumination was controlled by ion exchange of zeolite with alkali or alkaline earth metals. These results confirm that H+ ions catalyze the dealumination reaction from the zeolite framework and that hydrolysis of the Si-OM-Al bond formed by ion exchange does not occur under the steaming conditions adopted in this experiments. © 1989, The Chemical Society of Japan. All rights reserved.