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

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 Mn^4+/3+ to form NO₂ among three pathways, reveals the reason of high NO_x conversion of the catalyst at medium and low temperatures.

1. Download : Download high-res image (64KB)
2. Download : Download full-size image

     

事故致因“2-4”模型的内涵解析及第6版的研究

为使事故致因“2-4”模型(24Model)在追溯事故原因和制定事故预防对策时取得更好的应用效果,有必要对24Model的内涵进行科学解析。通过文献分析和对比研究,阐述24Model的逻辑结构、原因模块的科学内涵、主要特点。研究结果表明:24Model的主要理论基础,一是HEINRICH、BIRD等提出与改进的多米诺骨牌系列模型,二是REASON提出、SHAPPELL等具体化的瑞士奶酪系列模型和人因分类系统,三是STEWART提出的卓越安全管理模型;静态24Model的逻辑结构以因果关系建立,它属于因果顺序类事故致因模型;静态24Model中事故的直接、间接、根源、根本原因的含义可以从上述3大类事故致因模型、管理体系标准和安全文化的定义中找到根据;动态24Model靠行为演化关系建立逻辑结构,其充分表达自身的系统性、动态性、非线性,并且依靠组织行为即影响行为、个体行为即操作行为,构成一个行为演化系统。     

Drivers of temporal variations in fish assemblages from mangrove creeks in Beihai,southern China

Environmental Science and Pollution Research - Mangroves are regarded as important settlement grounds and nurseries for fishes due to the sheltered nature of these ecosystems. To identify the...     

Hydrochemical patterns indicating hydrological processes with the background of changing climatic and environmental conditions in China: a review

Environmental Science and Pollution Research - In the background of global climate and environmental change, the hydrochemical characteristics of water bodies present significant instability to all...