Revealing the Excellent Low-Temperature Activity of the FeCeO-S Catalyst for NH-SCR: Improvement of the Lattice Oxygen Mobility.

The development of selective catalytic reduction catalysts by NH(NH-SCR) with excellent low-temperature activity and a wide temperature window is highly demanded but is still very challenging for the elimination of NO emission from vehicle exhaust. Herein, a series of sulfated modified iron-cerium composite oxide FeCeO-S catalysts were synthesized. Among them, the FeCeO-S catalyst achieved the highest NO conversion of more than 80% at temperatures of 175-375 °C under a gas hourly space velocity of 100000 h. Sulfation formed a large amount of sulfate on the surface of the catalyst and provided rich Brønsted acid sites, thus enhancing its NH adsorption capacity and improving the overall NO conversion efficiency. The introduction of Ce is the main determining factor in regulating the low-temperature activity of the catalyst by modulating its redox ability. Further investigation found that there is a strong interaction between Fe and Ce, which changed the electron density around the Fe ions in the FeCeO-S catalyst. This weakened the strength of the Fe-O bond and improved the lattice oxygen mobility of the catalyst. During the reaction, the iron-cerium composite oxide catalyst showed higher surface lattice oxygen activity and a faster replenishment rate of bulk lattice oxygen. This significantly improved the adsorption and activation of NO species and the activation of NH species on the catalyst surface, thus leading to the superior low-temperature activity of the catalyst.