Acidity modification during the agglomeration of ZSM-5 with montmorillonite

Ammonia TPD analyses of ZSM-5 zeolites of three Si/Al ratios (15, 30, 43) agglomerated with sodium montmorillonite revealed a noticeable modification on the acid properties of the bound zeolites as compared with the raw materials. An initial increase of the proportion of the weak acidity was found on the agglomerated zeolites, though the total and strong acidity decreases. The higher the Si/Al ratio of the zeolite, the higher is this increase. After several steps of ion exchange of the bound zeolites, the acidity reaches the expected values again, and the total and strong acidities are enhanced at the expense of the weak acidity. These results were related to a solid-state ion exchange between protons of the zeolite and cations of the clay during the calcination subsequent to the agglomeration.