Influence of Tungsten-Doping on the Acid Sites and Redox Properties of COS+CS2 Sulfating Ce0.5Fe0.5Ox-S Catalyst for NH3-SCR Reactionc : Regulating of Promoted Fe-W Interaction on the Formation of Sulfate Species

Herein, as typical solid acidic oxides, Tungsten was doped into the Ce0.5Fe0.5Ox-S catalyst to modulate its gas-phase sulfation by organic COS + CS₂, which enhanced the NH₃-SCR activity at low-medium temperatures, with an optimal doping molar ratio of W/(Ce + Fe) is 0.3. The characterization indicated that tungsten doping inhibited the adsorption and conversion of COS+CS2 over the catalyst due to the enhanced interaction between iron and tungsten species. This effect diminished the diffraction peaks of iron sulfate and α-Fe2O3 at a W/(Ce + Fe) ratio of 0.5. The promoted Fe–W interaction also increased oxygen vacancies and enriched the pore structure. However, crystalline WO₃ formed at high doping levels shielded the Raman signals of cubic fluorite CeO2 and surface oxygen vacancies, partially blocking pores and reducing the BET surface area. Interestingly, this promoted interaction increased the surface concentrations of both Ce3+ and Fe3+, and the Ce0.5Fe0.5W0.3Ox-S catalyst even presented a larger surface concentration of Fe species than the Ce0.5Fe0.5Ox-S catalyst, although tungsten doping decreased the concentration of Ce species significantly. Furthermore, this promoted interaction reduced the amount of sulfates formed in the catalyst by restraining the gas-phase sulfation of Ce/Fe species, thereby regulating the total acid sites and weak acid sites/total acid sites proportion of Ce0.5Fe0.5Ox-S catalyst due to the different roles of the solid acidity of tungsten oxides and S6+ species in the formation of acid sites in W-doped Ce0.5Fe0.5Ox-S catalyst. It was found that both high levels of sulfate ions and tung-ten doping contributed to increasing the total acid sites of the catalyst.