Calcination vanadium migration

Transmission electron micrographs and XPS results have been used to show that a catalyst, with a high silica content in the matrix, prevents nickel dispersion (16,18). In fact, in a FCC with a Si-rich (Si/Al = 4.3) surface, XPS data has indicated that calcination and steaming cause nickel (and vanadium) migration to the cracking catalyst surface where nickel sinters. As a result, nickel crystallites 50... 

In order to clarify the role of steaming on vanadium migration, the EuY component doped with V (EuYV) was calcined, prior to being mixed with the gel. The SEM-EDX spectra of the steamed sample, (EuYV(p)CAAAS), are illustrated in Fig. 3. Corresponding analytical data are given in Table I. 

In summary, the results of Figs. 1-6 reveal that calcination of the porphyrin complex induce vanadium migration and that V mobility is minimized when V is initially placed on the gel. Calcination of V-loaded supports prior to mixture formation minimizes V-loses during steaming. 

If vanadyl naphthenate is used, minimal migration from the matrix to the zeolite and little or no V-migration from the zeolite to the matrix occur during calcination. Steaming induces some V-migration from the matrix to the zeolite but does not enhance V-migration from the zeolite to the matrix suggesting that vanadium is preferentially associated with the zeolite. 

In contrast, if vanadium porphyrin is used, calcination causes about 80% of the vanadium initially deposited onto the zeolite to move to the matrix. There is much less metal migration of the porphyrin complex from the matrix to the zeolite, indicating that vanadium prefers to remain in the matrix after calcination. During steaming, additional V-migration occurs and V-losses attributed to the formation of volatile V-compounds are observed. 

To understand the effects of the different ligands on V-migration during thermal treatments, vanadyl naphthenate precursor has also been used as dopants. The results for two calcined samples (EuYV(n)AAAC and AAAV(n)EuYC), are presented in Figs. 7 and 8, respectively. In contrast to the results shown in Fig. 1-6, no measurable V migration occurs from the zeolite to the matrix (Fig. 7) and only a trace of V moves from matrix to the zeolite (Fig. 8). Thus vanadium precursors can alter V mobility during calcination... 

Calcination. Based on the above data and other reports concerning surface vanadium species (12), migration mechanisms may be different for catalysts loaded with metals containing porphyrin or naphthenate ligands. 

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