Influence of CeO2 modification on the properties of Fe2O3–Ti0.5Sn0.5O2 catalyst for NO reduction by CO

Abstract

Fe₂O₃–CeO₂–Ti_0.5Sn_0.5O₂ catalysts were prepared by a wet impregnation method and were characterized using XRD, LRS, EPR, H₂-TPR, in situ IR, as well as the activity test for the removal of NO by CO. The results showed that the Fe₂O₃ and CeO₂ are highly dispersed on the surface of Ti_0.5Sn_0.5O₂ (the loading of Fe₂O₃ and CeO₂ are 1.2 mmol Fe per 100 m² and 0.4 mmol Ce per 100 m², respectively). When the iron oxide loading is increased, the isolated Fe³⁺ ions change into the polymeric Fe³⁺ clusters and ceria addition also further promotes the formation of polymeric Fe³⁺ clusters. Catalysts modified with ceria display better performance in activity, and this would result from the formation of the more polymeric Fe³⁺ clusters, which are more easily reduced to Fe²⁺ ions under CO atmosphere. In situ FT-IR results indicated that the Fe²⁺ ions generated from the reduction of Fe³⁺ ions are primary active sites for NO + CO reactions. A possible reaction mechanism is tentatively proposed. In the reaction atmosphere, NO adsorbed on the surface of the catalysts forms several types of nitrite species. With the increase of temperature, bridging bidentate nitrate species transform into chelating nitro species, which react with CO gas to produce CO₂ + N₂O. When temperature reaches beyond 200 °C, NO adsorbed on Fe²⁺ ions (reduction of Fe³⁺ ions) reacts with carbonate species adsorbed on the surface of the catalysts, and produces CO₂ + N₂.