Structure stabilization of zeolite Y induced by yttrium and its role in promoting n-docosane conversion

Abstract

Rare earth (RE)-exchanged zeolite Y is the major active component of fluid catalytic cracking (FCC) catalysts. Herein, a series of yttrium (Y³⁺)-exchanged zeolites Y was prepared by the ion-exchange method, and the location of Y³⁺ ions in the Y³⁺-exchange zeolite NaY was determined by fitting synchrotron radiation X-ray powder diffraction (XRPD) pattern combined with the infrared spectra in the hydroxyl stretching region. In analogy to lanthanum (La³⁺)-exchanged zeolite Y, Y³⁺ ions were preferentially located inside the sodalite units near the double six-membered rings (D6R's), octahedrally coordinating to three framework oxygens and to three H₂O molecules (or OH groups) in close proximity. The substitution of Y³⁺ ions for counter-ions Na ⁺ caused a noticeable shrinkage of the unit cell due mainly to the relatively small ionic radius and high charge density of Y³⁺ ions. As a consequence, the Y³⁺-exchanged HY-based FCC catalyst exhibited improved steam stability, and higher selectivity for high-value products (liquefied petroleum gas and C₅+gasoline) in n-docosane cracking compared with the La³⁺-exchanged HY-based catalyst.