Catalytic performance and reaction mechanisms of NO removal with NH3 at low and medium temperatures on Mn-W-Sb modified siderite catalysts

Xiang Ling , Guihuan Yao , Yuliang Wei , Keting Gui


Received April 10, 2021,Revised , Accepted June 24, 2021, Available online August 02, 2021

Volume 34,2022,Pages 126-139

Iron-based catalysts have been explored for selective catalytic reduction (SCR) of NO due to environmentally benign characters and good SCR activity. Mn-W-Sb modified siderite catalysts were prepared by impregnation method based on siderite ore, and SCR performance of the catalysts was investigated. The catalysts were analyzed by X-ray diffraction, H2-temperature-programmed reduction, Brunauer-Emmett-Teller, Thermogravimetry-derivative thermogravimetry and in-situ diffused reflectance infrared Fourier transform spectroscopy (DRIFTS). The modified siderite catalysts calcined at 450°C mainly consist of Fe2O3, and added Mn, W and Sb species are amorphous. 3Mn-5W-1.5Sb-siderite catalyst has a wide temperature window of 180-360°C and good N2 selectivity at low temperatures. In-situ DRIFTS results show NH4+, coordinated NH3, NH2, NO3 species (bidentate), NO2 species (nitro, nitro-nitrito, monodentate), and adsorbed NO2 can be discovered on the surface of Mn-W-Sb modified siderite catalysts, and doping of Mn will enhance adsorbed NO2 formation by synergistic catalysis with Fe3+. In addition, the addition of Sb can inhibit sulfates formation on the surface of the catalyst in the presence of SO2 and H2O. Time-dependent in-situ DRIFTS studies also indicate that both of Lewis and Brønsted acid sites play a role in SCR of NO by ammonia at low temperatures. The mechanism of NO removal on the 3Mn-5W-1.5Sb-siderite catalyst can be discovered as a combination of Eley-Rideal and Langmuir-Hinshelwood mechanisms with three reaction pathways. The mechanism of NO, oxidized by synergistic catalysis of Fe3+ and Mn4+/3+ to form NO2 among three pathways, reveals the reason of high NOx conversion of the catalyst at medium and low temperatures.
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