Revealing the Excellent Low-Temperature Activity of the Fe 1- x Ce x O δ -S Catalyst for NH 3 -SCR: Improvement of the Lattice Oxygen Mobility.

The development of selective catalytic reduction catalysts by NH 3 (NH 3 -SCR) with excellent low-temperature activity and a wide temperature window is highly demanded but is still very challenging for the elimination of NO x emission from vehicle exhaust. Herein, a series of sulfated modified iron-cerium composite oxide Fe 1- x Ce x O δ -S catalysts were synthesized. Among them, the Fe 0.79 Ce 0.21 O δ -S catalyst achieved the highest NO x 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 NH 3 adsorption capacity and improving the overall NO x 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 0.79 Ce 0.21 O 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 x species and the activation of NH 3 species on the catalyst surface, thus leading to the superior low-temperature activity of the catalyst.