Effect of the binary and ternary exchanges on crystallinity and textural properties of X zeolites

Abstract

The ionic exchange of the NaX zeolite by Cu 2+ and/or Zn 2+ cations is progressively driven while following the development of some of its characteristic: crystallinity by XR diffraction, profile of isotherms, RI criterion, isosteric adsorption heat and microporous volume using both the Dubinin–Radushkevich (DR) equation and the t-plot through the Lippens–de Boer method which also makes it possible to determine the external surface area. Results show that the cationic exchange process, in the case of Cu 2+ introduced at higher degree, is accompanied by crystalline degradation for Cu( x)X, in contrast to Zn 2+-exchanged zeolite X. This degradation occurs without significant presence of mesopores, because the RI criterion values were found to be much lower than 2.2. A comparison between the binary and ternary exchanges shows that the curves of CuZn( x)X are clearly below those of Zn( x)X and Cu( x)X, whatever the examined parameter. On the other hand, the curves relating to CuZn( x)X tend towards those of Cu( x)X. This would again confirm the sensitivity of the crystalline structure of CuZn( x)X with respect to the introduction of Cu 2+ cations. An original result is the distortion of the zeolitic framework of X zeolites at middle exchange degree, when Cu 2+ competes with another divalent cation, such as Zn 2+, for the occupancy of sites distributed within zeolitic cavities. In other words, the ternary exchange accentuates the crystalline degradation of X zeolites. An unexpected result also is the noncorrelation between crystal damage and the external surface area.