Influence of calcination temperature on the evolution of Fe species over Fe-SSZ-13 catalyst for the NH3-SCR of NO

Abstract

To shed light on the relationships among catalyst calcination temperature, physicochemical properties and catalytic properties of Fe-SSZ-13, a series of catalysts prepared by aqueous post-synthetic exchange and calcined at different temperatures are characterized and evaluated in NH3-SCR reaction. The characterizations and kinetic analysis indicate that the calcination temperature has a great effect on the acidity, Fe species distribution and catalytic properties of the Fe-SSZ-13 catalyst. The rise of calcination temperature decreases the low-temperature activity (< 425℃) and conversely improves the high-temperature activity of Fe-SSZ-13. It could be attributed to the following reasons: under low calcination temperatures, more isolated Fe3+ ions are maintained which can behave as Lewis acid sites and active sites in low reaction temperatures. Simultaneously, stronger surface acidity helps to alleviate NH3 inhibition effect at low temperatures, resulting in good low-temperature activity. On the other hand, the high calcination temperature brings about slight aggregation of isolated Fe3+ to form dimeric/oligomeric Fe clusters, leading more superior high-temperature activity. On the whole, the major active Fe species as well as the contribution of acid sites for low/high temperature activity are different. It could be concluded that the isolated Fe3+ ions and oligomeric Fe clusters are the active sites for low/high SCR reaction temperature, respectively. And zeolite acidity plays a more important role in low-temperature SCR reaction catalyzed by Fe-SSZ-13.