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排序方式: 共有625条查询结果,搜索用时 15 毫秒
81.
《Advanced Powder Technology》2022,33(4):103527
CeO2/Co/C dodecahedrons composites with excellent microwave absorption performance were synthesized by using a hydrothermal method. ZIF-67/CeO2 was first prepared by introducing CeO2 into the precursor of ZIF-67 and then CeO2/Co/C composite was obtained after heat treatment. Impedance matching of the samples could be well adjusted by controlling the content of CeO2. Unique dodecahedral structure for more interfacial reflection and cerium dioxide oxygen vacancies enhance microwave absorption performance. Specifically, the CeO2/Co/C exhibited a minimum reflection loss of ?68.83 dB is observed at 5.92 GHz, while the thickness was 3.69 mm. The introduction of CeO2 effectively enhanced the impedance matching of the materials and improved the microwave absorption performance. Therefore, this CeO2/Co/C composite is a promising microwave absorber material with high performance. 相似文献
82.
Leonid V. Gorobinskii Gleb Yu. Yurkov Dmitry A. Baranov 《Microporous and mesoporous materials》2007,100(1-3):134-138
Cerium oxide nanoparticles modified montmorillonite was obtained by interaction of a clay with (NH4)2Ce(NO3)6. The mean size of cerium oxide nanoparticles in clay was at 3.5 nm. The product was an amorphous solid and showed high permanent porosity and stability at high temperatures. The amorphous structure of the sample was proven by X-ray diffraction and electronic diffraction. The porous structure was studied by means of chemisorption and it was shown that samples calcined at 550 °C had SBET = 239 m2/g; micropore volume = 0.1839 cm3/g; average pore diameter = 3.07 nm. 相似文献
83.
Minimizing bromate formation with cerium dioxide during ozonation of bromide-containing water 总被引:7,自引:0,他引:7
This work investigated the effect of several metal oxides including alpha-FeOOH, alpha-Fe(2)O(3), gamma-FeOOH, and CeO(2) on bromate formation potential (BFP) during ozonation of bromide-containing water. Results indicate that CeO(2) could most effectively minimize the BFP among these metal oxides taking ozonation alone as control. The BFP minimization by O(3)/CeO(2) favored a relatively low Br(-) concentration (i.e., <1.0mgL(-1)) and pH<7. Water temperature ranging from 5 to 25 degrees C had no significant impact on the percent reduction of BrO(3)(-). Further investigation indicates that the effective BFP minimization can be ascribed to neither the surface adsorption of BrO(3)(-) or Br(-) on CeO(2) nor the surface reduction of BrO(3)(-) to HOBr/OBr(-) by CeO(2). It seems to have relationship with the activity of surface Ce(IV) sites. The CeO(2) can lower the concentration of H(2)O(2) which is formed during ozone decomposition and promotes BrO(3)(-) formation. Another possible reason for the BFP minimization is that the CeO(2) could possibly reduce BrO() to HOBr/OBr(-) during the decomposition of H(2)O(2). 相似文献
84.
Yttrium oxide doped with cerium (Y2O3:Ce3+) blue emitting phosphors was prepared by a new method called the bicontinuous cubic phase (BCP) method. The experimental results showed that the prepared precursors were amorphous yttrium hydroxide with a spherical shape and primary size 30-50 nm. After heat treatment, high crystallinity and luminescence efficiency phosphors were obtained. The obtained Y2O3:Ce3+ phosphors had a strong blue emitting at 400 nm. The optimum Ce3+ concentration was 1 mol% to obtain the highest PL intensity. This study indicated that the calcining temperature of 700 °C needed for high luminescence efficiency in this work is much lower than 1000 °C or above needed for the conventional solid-state method. 相似文献
85.
Cerium ion luminescence in crystalline hosts forms the basis of many blue phosphor and scintillator technologies. We report the synthesis of luminescent single crystals of cerium dicyanoargentate. The luminescence properties are characterized using both steady-state and time-resolved spectroscopy. The broad, overlapping dicyanoargentate and Ce3+ emissions are decomposed into three Gaussians, revealing the characteristic dicyanoargentate emission at 350 nm while the Ce3+ 5d–4f transitions are observed at 359 nm and 391 nm. Excitation measurements show that the 4f–5d Ce3+ absorption overlaps the 320 nm emission of the dicyanoargentate ions, leading to a strong coupling between the dicyanoargentate energy donors and Ce3+ acceptors. We conclude that the cerium is excited through an energy transfer process from the dicyanoargentate species, resulting in strong room temperature luminescence. 相似文献
86.
Şenol Sert Ceren Kütahyali Süleyman İnanZeynep Talip Berkan ÇetinkayaMeral Eral 《Hydrometallurgy》2008
The biosorption of lanthanum and cerium by leaves powder of Platanus orientalis was separately determined at varying experimental conditions using a batch technique. The effects of initial pH, contact time, initial metal ion concentration and temperature were investigated. The Langmuir and Freundlich isotherms were applied to represent the adsorption process. Langmuir isotherm fits the experimental data quite well. The Langmuir monolayer capacity of the sorbent is 28.65mg g− 1 and 32.05mg g− 1 for La and Ce(III), respectively. Thermodynamic parameters such as standard enthalpy (ΔH°), entropy (ΔS°) and free energy (ΔG°) were calculated from the slope and intercept of the plots of lnKd versus 1/T. The results indicated that sorption was endothermic and spontaneous in nature. The work reveals that powdered leaf of Platanus orientalis is a good choice as a biosorbent for the recovery of lanthanum and cerium from aqueous solution. 相似文献
87.
《International Journal of Hydrogen Energy》2020,45(46):24595-24603
Ce-promoted Ni/Al2O3 catalysts with Ce contents of 0, 5, 10, 15, and 20 wt% were investigated for CO2 methanation. Ni/15Ce/Al2O3 showed good selectivity and catalytic performance in CO2 methanation and remained stable at 350 °C for 80 h with minor fluctuations. Interactions between Ni and the Ce/Al2O3 support was characterized using X-ray diffraction, temperature-programmed reduction of H2, temperature-programmed desorption of CO2, X-ray photoelectron spectroscopy, Raman spectroscopy, and thermogravimetric analysis. Addition of Ce did not increase the catalytic surface area, which can significantly enhance the heterogeneous catalytic activity. However, XPS analysis showed that the Ce on the Ni/Al2O3 catalyst changed the surface electron states of Ni, Ce, and O. Additionally, CO2 adsorption/desorption was confirmed to be related to the amount of Ce present on Ni/Al2O3 by TGA and CO2-TPD. The Ce addition thus played an important role in determining the CO2 adsorption, desorption, and conversion. 相似文献
88.
Kai Shen Mingxiang Jiang Xinwei Yang Weizhong Zhou Qiguang Dai Xingyi Wang Li Wang Yun Guo Yanglong Guo Wangcheng Zhan 《中国稀土学报(英文版)》2023,41(4):523-530
The cerium-based catalysts were investigated for the catalytic co mbustion of trichlo roethylene(TCE) and exhibit a surprising catalytic activity.MnOx was doped into CeO2 by a citric acid(CA) sol-gel method,and the effect of Mn content on the physicochemical properties and catalytic activities of MnOx-CeO2 mixed oxides was investigated systemically.The introduction of MnOx into CeO2 can evidently improve the catalytic activity and... 相似文献
89.
《能源学会志》2020,93(2):666-678
Coal-fired power plant is the largest anthropogenic mercury source. Active carbon injection technique has been widely used to control the mercury emissions. However, high operation cost limits its development and it is necessary to find other potential mercury sorbents. In this study, raw semi-coke and a series of novel cerium (Ce) modified semi-cokes were synthesized and utilized for removing elemental mercury (Hg0) from simulated flue gas. It is noteworthy that the efficiencies were tested without hydrogen chloride (HCl) in order to evaluate the sorbents efficacy for low-chlorine (Cl) coal. The results show that the modified sorbents exhibited the best performance at 150 °C. The performance of sorbent could be reinforced due to the existence of oxygen (O2), nitric oxide (NO) and HCl. The adverse effect caused by sulfur dioxide (SO2) reduced dramatically after Ce modification. The negative impact of ammonia (NH3) on Hg0 removal in this study could be neglected owing to the tiny concentration of NH3. Raw semi-coke provided sufficient carbon content, which is favorable to mercury adsorption. As Ce loading increased, the carbon structure changed and the crystal of cerium oxide was formed in the modified semi-coke. The mass fraction of cerium oxide on the sorbent was over 4.4% when the concentration of Ce modification solution was higher than 0.2 mol L−1. The redox reaction activity and the oxygen storage ability of Ce3+/Ce4+ gave a huge boost to the performance of modified semi-coke. The addition of Ce also had an impact on the proportion of oxygen species. 相似文献
90.
Radosław Dębek Monika Motak Maria Elena Galvez Teresa Grzybek Patrick Da Costa 《International Journal of Hydrogen Energy》2017,42(37):23556-23567
Zr and Ce promoted hydrotalcite-derived materials were tested as a catalysts for dry reforming of methane. Zirconium species were introduced into hydrotalcite brucite-like layers, while cerium species were deposited on the external surfaces of crystallites. Three catalysts with Ce/Zr molar ratio of 1.2, 0.6 and 0.3 were synthesized, tested in dry reforming at 550 °C and subsequently characterized with the aid of XRD, XRF, FTIR, H2-TPR, CO2-TPD and TG techniques. Promotion with both Ce, Zr resulted in decrease catalytic activity, however, stability of materials was significantly increased, which could be attributed to increased concentration of strong basic sites. The effect of Ce/Zr molar ratio was mainly dependent on the position of Zr species in brucite-like layers or in mixed ceria–zirconia on catalyst surface and influenced materials basicity, reducibility and stability in DRM. 相似文献