Simultaneous NO Reduction and Hg0 Oxidation over La0.8Ce0.2MnO3 Perovskite Catalysts at Low Temperature
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La1–xAxMn1–yByO3 (A = Ca, Sr and Ce, B = Cu, Co and Fe, x = 0/0.2, y = 0/0.2) perovskite catalysts were employed for simultaneous NO and Hg0 removal. The perovskite structure is beneficial for low temperature catalysis. The substitution of A-site cations with cerium (Ce) cations significantly improved the catalytic activity of perovskite catalyst. 90% NO conversion and 98% Hg0 oxidation was attained using La0.8Ce0.2MnO3 catalyst at 200 °C. Hg0 oxidation posed negligible effect on NO reduction. Compared to the N2 plus 4% O2 atmosphere, Hg0 oxidation was significantly facilitated by selective catalytic reduction atmosphere. The enhancement in Hg0 oxidation was probably attributed to NO2 originated from NO. Furthermore, a possible reaction mechanism was proposed, in which surface oxygen, Mn4+ and Ce4+ contributed to NO and Hg0 removal. Such knowledge provides useful information for the development of effective and economical NO and Hg0 removal technology for coal-fired power plants.Keywords:
Selective catalytic reduction
Cerium oxide
Reducing atmosphere
Selective catalytic reduction of NOx with NH3(NH3-SCR) is the main technology to remove NOx from coal-fired power plants and diesel exhaust.The progress in cerium oxide-based catalysts for NH3-SCR was reviewed.The effects of different supports,preparation methods and doping elements on catalytic activity and sulfur resistance were analyzed.The reaction mechanisms of NH3-SCR and the activation mechanism of NH3 and NO on cerium oxide-based catalysts were discussed in detail.The development trends of cerium oxide-based catalysts for selective catalytic reduction of NOx with NH3 were outlined.
Selective catalytic reduction
Cerium oxide
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Silver-cerium nanoparticles had been successfully synthesized using the sol-gel method by silver nitrate as a source of silver and cerium nitrate hexahydrate as a source of cerium. The synthesized silver-cerium nanoparticles had been characterized by X-ray diffraction,transmission electron microscopy, and scanning electron microscopy-energy dispersive X-ray. Based on the results of XRD and TEM analysis showed silver-cerium nanoparticles were spherical with the dominant size range of 8.9 -12.73 nm. SEM-EDX analysis showed silver nanoparticles covered by cerium nanoparticles that were known as the core-shell structure. Silver nanoparticles doped with cerium nanoparticles (CeONP) showed an increase in inhibitory with an increase a zone of inhibition after being doped with cerium nanoparticles. The disinfection effect of Ag-doped CeONP was more pronounced on Staphylococcus aureus than Escherichia coli, although the difference was not wide.
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Cerium nitrate
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Hydrotalcite originated mixed metal Cu–Mg–Al oxide system was doped with various amounts of cerium (0.5 or 3.0 wt%) and tested in the role of catalysts for the selective catalytic oxidation of ammonia to dinitrogen (NH3-SCO) and the selective catalytic reduction of NO with ammonia (NH3-SCR). The activating effect of cerium was observed in both studied processes. However, the CeO2 loading is a very important parameter determining catalytic performance of the studied samples. It was shown that an introduction of cerium into Cu–Mg–Al mixed oxide resulted in its significant activation in the low-temperature NH3-SCR process, independently of the CeO2 loading and a decrease in the efficiency of the NO reduction at higher temperatures, which was more significant for the catalyst with the lower cerium content. In the case of the NH3-SCO process, the introduction of cerium into Cu–Mg–Al mixed oxide resulted in the activation of the low temperature reaction, which was more intensive for the catalyst with lower cerium content. These effects were related to the presence of cerium in the form of crystallites of various size and therefore their different reducibility.
Hydrotalcite
Cerium oxide
Selective catalytic reduction
Mixed oxide
Ammonia production
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The H2 and CO productivity and reactivity of three-dimensionally ordered macroporous (3DOM) cerium and cerium-zirconium oxide upon H2O and CO2 oxidation at 1073K is presented in comparison to the productivity and reactivity of non-ordered porous and low porosity cerium oxide. The production of H2 and CO2 constitutes the second step of the two-step solar thermochemical H2O and CO2 splitting cycles. The 3DOM cerium oxide, with a specific surface area of 25 m2 g−1, increases the average H2 and CO production rates over the non-ordered porous cerium oxide with a specific surface area of 112 m2 g−1: the average H2 production rate increases from 5.2 cm3 g−1 min−1 to 7.9 cm3 g−1 min−1 and the average CO production rate increases from 7.7 cm3 g−1 min−1 to 21.9 cm3 g−1 min−1. The superior reactivity of 3DOM cerium oxide is attributed primarily to the stability of the 3DOM structure and also to the improved transport of reacting species to and from oxidation sites realized with the interconnected and ordered pores of the 3DOM structure. Doping the 3DOM cerium oxide with 20 mol% zirconia further stabilizes the structure and increases the average H2 and CO production rates to 10.2 cm3 g−1 min−1 and 22.1 cm3 g−1 min−1, respectively.
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The existence forms of cerium in ultra- IF steel,in which the contents of oxygen and sulphur were both less than 0.000 6%,were studied by chemical analysis,thermodynamic calculation,micro- examination and hardness measurement. And the effects of cerium on Al2O3 inclusions,microstructure and hardness were discussed. The results show that,when the cerium content was between 0.006 1% and 0.009 3%,the solid solubility of cerium range from 0.004 1%to 0.006 7%. About seventy percent of cerium is in the form of solid solution,the rest of cerium is in the form of inclusions,and there is no Ce- Fe intermetallic compound in the steel. By adding cerium,Al2O3 inclusions are modified into smaller globular Ce Al O3 inclusions. Cerium played a role in modifying inclusions in the steel. Cerium has the effect of refining the microstructures of the steel. The greater the amount of solid solution of cerium was,the finer the crystalline grains were. When the content of cerium are 0.006 1% and 0.009 3%,Rockwell hardness increases by 7.6% and 12.7% respectively compared with IF steel without cerium.
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The porous cerium dioxide films were prepared with cerium foils as raw materials by two-step anodization and heat treating method. The anodic cerium oxide films were heat treated in 25∼400°C respectively. The cerium dioxide films were characterized with X-ray diffraction (XRD), Fourier transform infrared (FTIR) techniques, energy-dispersive analyses of X-ray (EDAX) and scanning electron microcopy (SEM), respectively. The anodic cerium oxide film is composed of Ce(OH)3, CeO2 and Ce2O3. When the anodic cerium oxide films were heat treated in 300°C∼400°C for 2h, Ce(OH)3 and Ce2O3 in the anodic cerium oxide films may be converted to CeO2, and the heat treated anodic cerium oxide films are the cerium dioxide films. Water, ethylene glycol and CO2 are adsorbed in the anodic cerium oxide film. The adsorbing water, ethylene glycol and CO2 in the anodic cerium oxide film are removed at 300°C. The cerium dioxide film has strong absorption in the range of 1600∼4000cm-1. The structure of the cerium dioxide film is the porous.
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Anodizing
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This review focuses on various synthesis methods of cerium oxide nanoparticles and discusses their corresponding physical characteristics, anti-ROS and anti-inflammatory properties.
Cerium oxide
Scavenging
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The rekindled interest in the cerium oxide catalyst for pollution control applications, as well as the catalytic activity of the mixed oxides based on cerium is subject of this research work. Compositions of different sizes, shapes and surface types and their influence on the catalytic activity of the particles mentioned. Interpreted the catalytic behavior both cerium oxide and mixed oxides of cerium, the factors affecting the oxygen storage capacity, the chemistry that takes place on the surfaces of catalysts and mechanisms of catalytic reactions. Particular emphasis is given to mixed oxides of cerium-zirconium. The action of the supports in the mixed cerium - zirconium oxide examined quite extensively. Finally, reference is made to action of mixed oxides based on cerium as metallic catalyst supports.
Cerium oxide
Mixed oxide
Zirconium oxide
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