A series of single-phase T-structured NdSrCu1??xCoxO4?? with oxygen vacancies and T0-structured Sm1:8Ce0:2Cu1??xCoxO4?? (x:
0–0.4) with oxygen excess were prepared using ultrasound-assisted citric acid complexing method, and characterized by means of
techniques such as thermogravimetric analysis and NO temperature-programmed desorption (NO-TPD). The catalytic activities of these
materials were evaluated for the decomposition of NO. It was found that the NdSrCu1??xCoxO4?? catalysts were of oxygen vacancies
whereas the Sm1:8Ce0:2Cu1??xCoxO4?? ones possessed excessive oxygen (i.e., over-stoichiometric oxygen); with a rise in Co doping level,
the oxygen vacancy density of NdSrCu1??xCoxO4?? decreased while the over-stoichiometric oxygen amount of Sm1:8Ce0:2Cu1??xCoxO4??
increased. The NO-TPD results revealed that NO could be activated much easier over the oxygen-deficient perovskite-like oxides
than over the oxygen-excessive perovskite-like oxides, with the NdSrCuO3:702 catalyst showing the best e ciency in activating NO
molecules. Under the conditions of 1.0% NO/helium, 2800 hr??1, and 600–900°C, the catalytic activity of NO decomposition followed
the order of NdSrCuO3:702 > NdSrCu0:8Co0:2O3:736 > NdSrCu0:6Co0:4O3:789 > Sm1:8Ce0:2Cu0:6Co0:4O4:187 > Sm1:8Ce0:2Cu0:8Co0:2O4:104
> Sm1:8Ce0:2CuO4:045, in concord with the sequence of decreasing oxygen vacancy or oxygen excess density. Based on the results,
we concluded that the higher oxygen vacancy density and the stronger Cu3+/Cu2+ redox ability of NdSrCu1??xCoxO4?? account for the
easier activation of NO and consequently improve the catalytic activity of NO decomposition over the catalysts. 相似文献
Wet air oxidation (WAO) and catalytic wet air oxidation (CWAO) are efficient processes to degrade organic pollutants in water. In this paper, we especially reviewed the WAO and CWAO processes for phenolic compounds degradation. It provides a comprehensive introduction to the CWAO processes that could be beneficial to the scientists entering this field of research. The influence of different reaction parameters, such as temperature, oxygen pressure, pH, stirring speed are analyzed in detail; Homogenous catalysts and heterogeneous catalysts including carbon materials, transitional metal oxides and noble metals are extensively discussed, among which Cu based catalysts and Ru catalysts were shown to be the most active. Three different kinds of the reactor implemented for the CWAO (autoclave, packed bed and membrane reactors) are illustrated and compared. To enhance the degradation efficiency and reduce the cost of the CWAO process, biological degradation can be combined to develop an integrated technology.
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.