采用喷雾热分解法制备了钙钛矿型催化剂La0.7Sr0.3Mn1-xCoxO3-δ(x=0、0.3、0.5、0.7),利用X射线衍射(XRD)和扫描电子显微镜(SEM)对催化剂进行了表征,在微型固定床反应器上优化了催化剂的B位掺杂Co.在天然气发动机排放试验台架上进行了空燃比特性、CH4排放和发动机尾气排放达标等测试试验.结果表明:在La0.7Sr0.3Mn1-x Co x O3-δ中掺杂适宜量的Co有助于提高催化剂的催化燃烧活性,改善催化剂比表面积和孔容积.当Co掺杂量为0.5时,所形成的La0.7Sr0.3Mn0.5Co0.5O3-δ催化剂对天然气发动机尾气排放物呈现出良好低温催化燃烧活性,对甲烷催化燃烧的起燃温度(T10)、半转化温度(T50)和完全转化温度(T90)分别为175、350和400℃,CO、NO x、非甲烷碳氢化合物(NMHC)和CH4的最大比排放量分别为3.01、1.72、0.31和0.85 g·kW-1·h-1,达到了国Ⅴ排放法规对天然气发动机有害排放物的限值要求,表明了La0.7Sr0.3Mn0.5Co0.5O3-δ适宜用于天然气发动机尾气低温催化燃烧的催化剂. 相似文献
The reduction of nitrate contaminant in groundwater has gained renewed and intensive attention due to the environmental problems and health risks. Catalytic denetrification presents one of the most promising approaches for the removal of nitrate from water. Catalytic nitrate reduction from water by powder catalysts and catalytic membrane in a batch reactor was studied. And the effects of the initial concentration, the amounts of catalyst, and the flux H2 on the nitrate reduction were also discussed. The results demonstrated that nitrate reduction activity and the selectivity to nitrogen gas were mainly controlled by diffusion limitations and the mass transfer of the reactants. The selectivity can improved while retaining a high catalytic activity under controlled diffusion condition or the intensification of the mass transfer, and a good reaction condition. The total nitrogen removal efficiency reached above 80%. Moreover, catalytic membrane can create a high effective gas/liquid/solid interface, and show a good selectivity to nitrogen in comparative with the powder catalyst, the selectivity to nitrogen was improved from 73.4 % to 89.4%. 相似文献
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.