A study on the selective catalytic reduction of NO by ammonia on sulphated iron-based catalysts

A series of sulphated iron-based catalysts was prepared via an impregnation method by changing the loading content of Fe³⁺ and SO₄ ^2- on ZrO₂, and their performance in the selective catalytic reduction (SCR) of NO by ammonia was investigated. The NO conversion exhibited large differences among the sulphated iron-based catalysts. To explore the synergistic mechanism of iron and sulphates, XRD, BET, H₂-TPR, XPS, TPD and in situ DRIFTS were used to characterize the catalysts, and it was found that among all the catalysts, the NO conversion by Fe₂SZr was greater than 90% at 350-450 °C. The results indicated that the interaction between Fe³⁺ and SO₄ ^2- can have an effect on the redox ability, acid sites, and adsorption of NO and NH₃. With an increase in the content of Fe³⁺, the redox activity of the catalyst and the adsorption of ammonia improved at medium and low temperatures. However, at higher temperatures, an increase in Fe³⁺ led to a decrease in the conversion of NO due to the enhanced oxidation of NH₃. At medium and low temperatures, an increase in the content of SO₄ ^2- decreased the concentration of Fe³⁺ on the surface of the catalyst and inhibited the adsorption of NO and NH₃. The addition of SO₄ ^2- reduced the redox activity of the catalyst and inhibited the oxidation reaction of NH₃, which follows the Eley-Rideal mechanism at high temperatures, further enhancing the SCR activity of the Fe S Zr catalyst.