SCANNING ELECTRON-MICROSCOPY ENERGY-DISPERSIVE X-RAY-ANALYSIS OF NICKEL MIGRATION IN MODEL FLUID CRACKING CATALYSTS

SEM/EDX (scanning electron microscopy/energy dispersive x-ray analysis) has been used to probe interparticle migration of nickel between an Eu3+-exchanged zeolite Y and AAA-alumina in model fluid cracking catalysts (FCC). Migration depends on the nature of nickel precursors and their loadings. No migration can be observed between the two components during calcination or steaming when nickel naphthenate is used and only 0.5 wt % Ni is loaded. When the loading is increased to 1 wt %, Ni does not migrate from the matrix to the zeolite or vice versa during calcination. Steaming induces about 20 to 30 % of the initially-deposited nickel to move from the zeolite to the matrix, but only trace migration is observed from the matrix to the zeolite. When 1.0 wt % Ni is loaded using nickel porphyrin, no migration from matrix to the zeolite occurs, as is the case for vanadyl porphyrin. Steaming allows some of the nickel that migrated to the matrix during calcination to move back to the zeolite. However, only a trace of Ni can migrate from the initially-deposited matrix to the zeolite during steaming. These results demonstrate that nickel preferentially remains in the matrix during steaming. When the matrix is not intimately contacted with the zeolite, nickel porphyrin molecules are removed from the zeolite to the gas phase during calcination. A particle contact mechanism prevails, however, when the two components are intimately contacted.