De–SOx additives based on mixed oxides derived from Mg,Al-hydrotalcite-like compounds containing Fe, Cu, Co or Cr

Mg,Al-hydrotalcite-like compounds (HTLCs) with an M3+/(M2+ + M3+) molar ratio equal to 0.25 in which Mg or Al were partially replaced by Cu, Co, Cr or Fe were prepared and used as precursors for different mixed oxides (MO): Cu–MO, Co–MO, Cr–MO or Fe–MO. These materials were evaluated for SOx removal under conditions similar to those found in the fluid catalytic cracking (FCC) regenerator. The following order of catalytic activity for SOx uptake was observed: Cu–MO > Co–MO > Fe–MO > Cr–MO. The regeneration of the sulfated additives was also studied and the results showed that the composition of the reductive stream influenced the regeneration profiles, the total quantity of sulfur released, and the reduction products distribution, in a specific way for each sample. These results could be related to the nature of the reducing agent and to the fact that the thermal stability and the reducibility of the sulfates are significantly affected by the metal with redox properties present in the additive.