A study on the selective catalytic reduction of NO x 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 Fe 3+ and SO 4 2- on ZrO 2 , and their performance in the selective catalytic reduction (SCR) of NO x by ammonia was investigated. The NO x conversion exhibited large differences among the sulphated iron-based catalysts. To explore the synergistic mechanism of iron and sulphates, XRD, BET, H 2 -TPR, XPS, TPD and in situ DRIFTS were used to characterize the catalysts, and it was found that among all the catalysts, the NO x conversion by Fe 2 SZr was greater than 90% at 350-450 °C. The results indicated that the interaction between Fe 3+ and SO 4 2- can have an effect on the redox ability, acid sites, and adsorption of NO x and NH 3 . With an increase in the content of Fe 3+ , the redox activity of the catalyst and the adsorption of ammonia improved at medium and low temperatures. However, at higher temperatures, an increase in Fe 3+ led to a decrease in the conversion of NO x due to the enhanced oxidation of NH 3 . At medium and low temperatures, an increase in the content of SO 4 2- decreased the concentration of Fe 3+ on the surface of the catalyst and inhibited the adsorption of NO x and NH 3 . The addition of SO 4 2- reduced the redox activity of the catalyst and inhibited the oxidation reaction of NH 3 , which follows the Eley-Rideal mechanism at high temperatures, further enhancing the SCR activity of the Fe x S y Zr catalyst.