Abstract
Hydrotalcite-derived Mg,Al-mixed oxides (MO) with variable Mg/Al ratios (3, 1, 1/3) were impregnated with 17 wt.% of CeO 2 and evaluated for SO x removal under conditions similar to those of FCC units. The catalyst with Mg/Al = 1, for which both an Mg(Al)O periclase-type and an MgAl 2O 4-spinel were present before sulfation, showed the best performance for both SO x uptake and catalyst regeneration. The results from TPR/MS and XRD along reduction indicate the existence of different species in the sulfated samples. The reduction of these sulfate species leads to the evolution of SO 2 or H 2S, Mg(Al)O being the solid product in any case. Our results do not support the assertion that the reduction of S 6+ to S 2− is a consecutive reaction. The evolution of SO 2 upon reduction decreases as the relative importance of the spinel-phase in the mixed oxides increases. The sulfates formed from the spinel-phase are more easily reduced than those from the periclase phase. The growth of the sulfate phase in the early stages of sulfation destroys the small mesopores of the mixed oxide. Upon regeneration, the sulfate phase is consumed and larger mesopores are formed.
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