title: Improvement of activity and SO₂ tolerance of Sn-modified MnOx-CeO₂ catalysts for NH₃-SCR at low temperatures.
abstract: The performances of fresh and sulfated MnOx-CeO₂ catalysts for selective catalytic reduction of NOx by NH₃ (NH₃-SCR) in a low-temperature range (T < 300 °C) were investigated. Characterization of these catalysts aimed at elucidating the role of additive and the effect of sulfation. The catalyst having a Sn:Mn:Ce = 1:4:5 molar ratio showed the widest SCR activity improvement with near 100% NOx conversion at 110-230 °C. Raman and X-ray photoelectron spectroscopy (XPS) indicated that Sn modification significantly increases the concentration of oxygen vacancies that may facilitate NO oxidation to NO₂. NH₃-TPD characterization showed that the low-temperature NH₃-SCR activity is well correlated with surface acidity for NH3 adsorption, which is also enhanced by Sn modification. Furthermore, as compared to MnOx-CeO₂, Sn-modified MnOx-CeO₂ showed remarkably improved tolerance to SO₂ sulfation and to the combined effect of SO₂ and H₂O. In the presence of SO₂ and H₂O, the Sn-modified MnOx-CeO₂ catalyst gave 62% and 94% NOx conversions as compared to 18% and 56% over MnOx-CeO₂ at temperatures of 110 and 220 °C, respectively. Sulfation of SnO₂-modified MnOx-CeO₂ may form Ce(III) sulfate that could enhance the Lewis acidity and improve NO oxidation to NO₂ during NH₃-SCR at T > 200 °C.
authors.affiliation: State Key Joint Laboratory of Environment Simulation and Pollution Control, School of Environment, Tsinghua University, Beijing 100084, China.
authors.forename: Huazhen
authors.initials: H
authors.lastname: Chang
authors.forename: Xiaoyin
authors.initials: X
authors.lastname: Chen
authors.forename: Junhua
authors.initials: J
authors.lastname: Li
authors.forename: Lei
authors.initials: L
authors.lastname: Ma
authors.forename: Chizhong
authors.initials: C
authors.lastname: Wang
authors.forename: Caixia
authors.initials: C
authors.lastname: Liu
authors.forename: Johannes W
authors.initials: JW
authors.lastname: Schwank
authors.forename: Jiming
authors.initials: J
authors.lastname: Hao
mesh_terms: D015502:Absorptiometry, Photon; D000641:Ammonia / Q000737:chemistry*; D002384:Catalysis; D002563:Cerium / Q000737:chemistry*; D003080:Cold Temperature; D008277:Magnesium Oxide / Q000737:chemistry*; D013458:Sulfur Dioxide / Q000737:chemistry*; D013818:Thermogravimetry; D014001:Tin / Q000737:chemistry*
chemical_list: D013458:Sulfur Dioxide; D002563:Cerium; D008277:Magnesium Oxide; C030583:ceric oxide; D014001:Tin; D000641:Ammonia