Revealing the Excellent Low-Temperature Activity of the Fe_1–<i>x</i>Ce_<i>x</i>O_δ-S Catalyst for NH₃-SCR: Improvement of the Lattice Oxygen Mobility

Abstract

The development of selective catalytic reduction catalysts by NH₃(NH₃-SCR) with excellent low-temperature activity and a wide temperature window is highly demanded but is still very challenging for the elimination of NO_<i>x</i> emission from vehicle exhaust. Herein, a series of sulfated modified iron-cerium composite oxide Fe_1-<i>x</i>Ce_<i>x</i>O_δ-S catalysts were synthesized. Among them, the Fe_0.79Ce_0.21O_δ-S catalyst achieved the highest NO_<i>x</i> conversion of more than 80% at temperatures of 175-375 °C under a gas hourly space velocity of 100000 h^-1. Sulfation formed a large amount of sulfate on the surface of the catalyst and provided rich Brønsted acid sites, thus enhancing its NH₃ adsorption capacity and improving the overall NO_<i>x</i> 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 Fe_0.79Ce_0.21O_δ-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_<i>x</i> species and the activation of NH₃ species on the catalyst surface, thus leading to the superior low-temperature activity of the catalyst.