ROLE OF THE AMORPHOUS MATRIX IN THE HYDROTHERMAL AGING OF FLUID CATALYTIC CRACKING CATALYSTS

The influence of hydrothermal ageing on a matrix-embedded lanthanum-exhanged zeolite Y has been reinvestigated using several physical techniques (IR, XRD, NMR and STEM). It was found that the crystallinity of LaY zeolite was totally preserved when the zeolite was incorporated into the amorphous matrix, while the same zeolite, if not embedded, lost 55% of its initial crystallinity upon steaming. In addition, a significant dealumination of the zeolite structure was observed. Direct local measurements of the chemical composition of the steamed catalyst using a STEM analytical microprobe showed that severe steaming induced material transportation between the zeolite and the matrix. Isotopic Si-29 labelling of the matrix combined with Si-29 MAS-NMR provided the decisive proof for a silicon transportation from the matrix toward the zeolite component and its subsequent reincorporation into the zeolite framework in the place of the expelled aluminium atoms. This phenomenon is thought to be responsible for the "healing" of matrix-embedded zeolites and therefore to explain their increased resistance against severe steaming conditions.