Promotion of NH3-SCR activity by sulfate-modification over mesoporous Fe doped CeO2 catalyst: Structure and mechanism

Abstract

The mesoporous Fe doped CeO2 catalyst after modifying organic sulfate functional groups show an excellent activity with above 80% NOx conversion in a temperature range of 250–450 °C. These organic-like sulfate groups bound to the Fe-O-Ce species leads to the strong electron interaction between Fe3+-O-Ce4+ species and sulfate groups, which modifies the acidity and redox properties of catalyst. The strong ability of S˭O/S-O in sulfate groups to accommodate electrons from a basic molecule is a driving force in the generation of acidic properties, and thus promotes to produce new Brønsted acid sites. The bondage of Fe-O-Ce species obviously inhibits the creation of thermostable bidentate NO3− species. Besides, the redox cycles between Fe3+ and Ce4+ are disrupted, thus inhibiting NH3 oxidation at medium-high temperatures and resulting in the increase of NOx conversion. Furthermore, the in situ DRIFTS results show that for the fresh samples, the coordinate NH3 reacts not only with NO3− through L-H mechanism, but also with oxygen species to form NOx. Differently for sulfated sample, the coordinate NH3 might react with achieved NO2 instead of the oxygen species through E-R mechanism, meanwhile the NH4+ could react with the NO3− species through L-H mechanism.