The selective catalytic reduction (SCR) technique that converts NO x from the outlet of industrial boilers at low temperature (<200 °C) requires catalysts that possess both the oxidization property of NO x and the adsorption ability to NH 3 . However, owing to unsuitable redox capacity, most NH 3 -SCR catalysts such as MnO 2 /TiO 2 and MnO 2 −CeO 2 /TiO 2 suffer from poor activity and N 2 selectivity and SO 2 poisoning. Benefiting from constructing mesoporous MnCeSmTiO x amorphous mixed oxides by the coprecipitation method, enhanced SO 2 -tolerant lowtemperature NH 3 -SCR performance was achieved. The MnCeSm-TiO x catalysts have an amorphous and mesoporous structure with a BET surface area of 214 m 2 •g −1 . The NO conversion could reach nearly 100% at 140−320 °C and maintain >90% at 400 °C and a gas hourly space velocity of 80,000 h −1 . The selectivity of N 2 could be maintained at ≈100% at 100−320 °C and stay at >90% up to 400 °C. Besides, the MnCeSmTiO x catalyst preserves higher catalytic performance after introducing H 2 O and SO 2 compared with the catalysts without adding Sm. The redox properties, acidic properties, and reaction intermediates of catalysts were analyzed by X-ray photoelectron spectroscopy, hydrogen temperatureprogrammed reduction, ammonia temperature-programmed desorption, oxygen temperature-programmed desorption, pyridine-IR, thermogravimetry−differential scanning calorimetry, and diffuse reflectance infrared Fourier transform. The synergistic effect of the Lewis acid sites and oxidation catalytic sites of mixed oxides serves for the conversion of NO to N 2 by following the Langmuir− Hinshelwood mechanism. Doping Sm into MnCeSmTiO x can increase oxygen vacancies and transfer electrons to Mn 4+ and Ce 4+ , which facilities the formation of active adsorbed NO 2 , bidentate nitrate, and bridging nitrate intermediates and suppresses SO 2 poisoning by inhibiting the oxidation of SO 2 by Mn 4+ and Ce 4+ . Our work could be beneficial to modulate the redox capacity of active sites on NH 3 -SCR catalysts so that NO x can be eliminated in complex flue gas at low temperatures.

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