Synthesis-Route Engineering of Cu–Sm–Ti Oxides for Coupled Low-Temperature NH₃-SCR and CO Oxidation

Low-temperature sintering flue gas contains both nitrogen oxides (NO_x) and carbon monoxide (CO), requiring bifunctional catalysts for concurrent pollutant abatement. Herein, CuSmTi composite oxides with an identical nominal composition were synthesized via impregnation, mechanical grinding, and sol–gel methods to examine the effects of preparation route on their structure, surface properties, and catalytic performance in coupled NH₃-SCR and CO oxidation. CuSmTi-SG exhibited the best performance, achieving >40% NO_x conversion at 125 °C, complete NO_x and CO conversion at 200 °C, and nearly 100% N₂ selectivity over 100–300 °C, with stable performance over 24 h. It possessed a higher surface area (131.4 m² g⁻¹), pore volume (0.230 cm³ g⁻¹), and smaller TiO₂ crystallite size (8.5 nm) than the other catalysts. Spectroscopic analyses showed that sol–gel synthesis altered the surface electronic states of Cu and Sm species, resulting in a higher Cu⁺ fraction and greater amounts of medium-to-strong Lewis acid sites and labile surface oxygen species. In situ DRIFTS indicated that CO oxidation proceeded predominantly via a Mars–van Krevelen mechanism over Cu⁺ sites, whereas NH₃-SCR mainly followed an Eley–Rideal pathway. CO and NH₃ preferentially interacted with different surface sites, resulting in limited mutual inhibition. These results demonstrate that the preparation route can modify the structure and surface chemistry of CuSmTi catalysts without changing their nominal composition, thereby affecting their performance in low-temperature NO_x and CO abatement.