Formation of Active Sites by Ion Exchange

Removal of sodium from the early Y-zeolites remained an urgent priority for catalyst manufacturers who were attempting to increase gasohne yield and obtain catalysts with higher thermal stabihty. Experimental woik with Y-zeohte had confirmed the benefits of a catalyst with low residual sodium content, but repeated exchange with ammonimn sdts was too expensive to be used commercially. Consequently the Y-zeolite produced commercially was not sufficiently stable. 

Early development work by Mobil had shown that the exchange of sodium with higher-valency ions, particularly those derived from rare earth metals, increased stability. Rare earth-exchanged NaY-zeolite (REY-zeolite) was not as easily dealuminated by steam and high temperatures in the regenerator as HY-zeolite. Consequently, catalysts manufactured from REY-zeolite were soon being used to maximize gasoline production in most FCC units. 

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