School of Mechanical and Power Engineering, Nanjing Tech University, Nanjing 211816, China.
School of Energy and Environment, Southeast University, Nanjing 210096, China.
J Environ Sci (China). 2022 May;115:126-139. doi: 10.1016/j.jes.2021.06.029. Epub 2021 Aug 2.
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, H-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 FeO, 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 N selectivity at low temperatures. In-situ DRIFTS results show NH, coordinated NH, NH, NO species (bidentate), NO species (nitro, nitro-nitrito, monodentate), and adsorbed NO can be discovered on the surface of Mn-W-Sb modified siderite catalysts, and doping of Mn will enhance adsorbed NO formation by synergistic catalysis with Fe. In addition, the addition of Sb can inhibit sulfates formation on the surface of the catalyst in the presence of SO and HO. 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 Fe and Mn to form NO among three pathways, reveals the reason of high NO conversion of the catalyst at medium and low temperatures.
铁基催化剂因其环境友好的特性和良好的 SCR 活性而被用于选择性催化还原（SCR）NO。本研究采用浸渍法以菱铁矿为原料制备了 Mn-W-Sb 改性菱铁矿催化剂，并考察了其 SCR 性能。采用 X 射线衍射、H 2-程序升温还原、BET、热重-差热分析和原位漫反射红外傅里叶变换光谱（DRIFTS）对催化剂进行了分析。在 450℃下煅烧的改性菱铁矿催化剂主要由 FeO 组成，添加的 Mn、W 和 Sb 物种为无定形。3Mn-5W-1.5Sb-菱铁矿催化剂在低温下具有较宽的 180-360°C 温度窗口和良好的 N 选择性。原位 DRIFTS 结果表明，Mn-W-Sb 改性菱铁矿催化剂表面存在 NH、配位 NH、NH、NO 物种（桥接）、NO 物种（硝态、硝基亚硝态、单齿）和吸附态 NO，Mn 的掺杂会通过与 Fe 的协同催化作用增强吸附态 NO 的形成。此外，在存在 SO 和 HO 的情况下，Sb 的添加可以抑制催化剂表面硫酸盐的形成。时间依赖性原位 DRIFTS 研究还表明，Lewis 和 Brønsted 酸位在低温下氨 SCR 中都发挥作用。3Mn-5W-1.5Sb-菱铁矿催化剂上 NO 去除的机制可以发现是 Eley-Rideal 和 Langmuir-Hinshelwood 机制的结合，有三种反应途径。在三种途径中，Fe 和 Mn 的协同催化作用将 NO 氧化为 NO 的反应机制，揭示了催化剂在中低温下具有高 NO 转化率的原因。
