Characterization of zinc oxide and zinc ferrite doped with Ti or Cu as sorbents for hot gas desulphurization

Abstract

Three series of samples based on zinc oxide and zinc ferrite doped with copper or titanium oxides have been prepared in order to improve their performance as regenerable sorbents for hot gas desulphurization. In each series the oxide concentration was varied over a broad range to enhance the formation of different chemical species. The stability against reducing agents and the performance of these sorbents were studied elsewhere. The characterization of fresh, sulphided and regenerated samples was undertaken using XRD, FT-Raman and XPS techniques. The addition of Ti increased the stability of ZnO against reducing agents such as H2, up to an atomic ratio Ti/Zn= 0.5 through the formation of Zn2TiO4. Furthermore, the Ti excess is segregated as TiO2. The addition of Cu to zinc ferrite did not affect the stability but improved the sorbent performance enhancing the ferrite formation and migrating to the sorbent surface during the calcination and regeneration steps. The addition of Ti to zinc ferrite prevented its decomposition into the two component oxides below 600°C stabilizing the structure through the inclusion of Ti in the ferrite lattice. In the sulphiding process Fe, Zn and Cu oxides were converted into the lowest oxidation state sulphides that facilitated the sorbent regeneration during the regeneration process.