Powder preparation and UV absorption properties of selected compositions in the CeO2-Y2O3 system

Several approaches have been investigated to prepare fluorite-type compositions within the (1−x) CeO₂-xYO_1.5 system. The optical properties of the resulting modified-ceria materials have been characterized in order to evaluate their potential abilities as inorganic UV absorbers. Diffuse reflectance analyses reveal a strong optical absorption between 390 and 400 nm for all substituted compositions and the spectral selectivities are estimated suitable for the targeted application. Additionally, time resolved microwave conductivity (TRMC) and phenol photodegradation analyses do not indicate any photocalatytic activity for these compositions. Aqueous colloidal suspensions of the Ce_0.7Y_0.3O_1.85 UV absorber have been carried out.     

Density functional theory study of formaldehyde adsorption and decomposition on Co-doped defective CeO_2(110) surface

Formaldehyde as an air pollutant to adverse health effects for humanity has been getting attention. The adsorption and dissociation of formaldehyde(HCHO) on the Co_xCe_(1-x_O_(2-δ)(110) surface were investigated by the density functional theory(DFT) calculations. We calculated the oxygen vacancy formation energy as the function of its site around dopant Co in detail. The results showed that Co doping was accompanied by compensating oxygen hole spontaneous formation.The adsorption configurations and bindings of HCHO at different locations on the Co_xCe_(1-x)O_2(110) were presented.Four possible pathways of oxidation of formaldehyde on the catalytic surface were explored. The results suggested that formaldehyde dissociation at different adsorption sites on the doped CeO_2(110) — first forming dioxymethylene(CH_2O_2)intermediate, and then decomposing into H_2O, H_2, CO_2, and CO molecules. It was found that the presence of cobalt and oxygen vacancy significantly prompted the surface activity of CeO_2.     

Deactivation studies of nano-structured iron catalyst in Fischer-Tropsch synthesis

A nano-structured iron catalyst for syngas conversion to hydrocarbons in Fischer-Tropsch synthesis (FTS) was prepared by micro-emulsion method. Compositions of bulk iron phase and phase transformations of carbonaceous species during catalyst deactivation in FTS reaction were characterized by temperature-programmed surface reaction with hydrogen (TPSR-H2), and XRD techniques. Many carbonaceous species on surface and bulk of the nano-structured iron catalysts were completely identified by combined TPSR-H2 and XRD spectra and which were compared with those recorded on conventional co-precipitated iron catalyst. The results reveal that the catalyst deactivation results from the formation of inactive carbide phases and surface carbonaceous species like graphite, and it will be increased when the particle size of iron oxides was reduced in FTS iron catalyst.     

Oxidative coupling of methane over （Na2WO4＋Mn or Ce）/SiO2 catalysts： In situ measurement of electrical conductivity

The effects of manganese oxide or ceria promoters on the performance of Na2WO4/SiO2 catalysts for oxidative coupling of methane (OCM) are reported. The OCM reaction was performed in a continuous-flow microreactor at 800 ℃, atmospheric pressure and under GHSV = 13200 ml gC-1at h-1. Catalysts were characterized by in situ conductivity measurement, FT-IR spectroscopy, XRD, SEM and temperature programmed reduction analysis. Manganese oxide promoted Na2WO4/SiO2 is considered as one of the active and selective ca...     

氧化铈纳米粒子光催化降解亚甲基蓝的动力学和机理

 CeO2 nanocrystals were synthesized by a simple precipitation method and calcination at 600 °C. (NH4)2Ce(NO3)6 and ammonia were used as precursors. The CeO2 nanoparticles were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, and N2 adsorption. The photodegradation of methylene blue catalyzed by CeO2 nanoparticles was studied under UV and sunlight irradiation. The highest degradation was obtained with 1.0 g/L CeO2 at pH 11 within 125 min. The pseudo first order rate constants of dye bleaching were calculated as 16.2x10-3 and 15.7x10-3 min-1 under UV and sunlight irradiation, respectively. The effect of iso-PrOH, iodide ion, and H2O2 was studied to predict the pathway of dye degradation. The obtained results indicate the effect of photogenerated holes in the degradation mechanism of the dye. Also, the photocatalytic activity of the prepared photocatalyst was studied in the presence of several negative ions.     

碱金属助剂对 Au-Pt/CeO2 催化剂催化水煤气变换反应活性的影响

 制备了碱金属 M (M = Na, K, Rb 和 Cs) 掺杂的 Au-Pt/CeO2 催化剂, 考察了其催化水煤气变换反应的活性, 并采用 X 射线衍射、H2 程序升温还原、紫外-可见漫反射光谱和 X 射线光电子能谱技术研究了 K 助剂对 Au-Pt/CeO2 催化剂结构和表面性质的影响. 结果表明, 添加少量电负性较低的 K 虽然使 Pt 的还原变得困难, 但有利于 Au 金属态的稳定, 并使催化剂表面 Ce3+ 富集而产生氧空位, 显著提高了 Au-Pt/CeO2 催化剂活性. 当 K 负载量为 0.025%, 反应温度 250 oC 时, CO 转化率可达 95%.     

Modifications of interface chemistry of LSM-YSZ composite by ceria nanoparticles

A porous composite electrode LSM-YSZ (lanthanum strontium manganite and yttria stabilized zirconia) was impregnated with different amounts of SDC (samarium substituted ceria) nanoparticles. The materials were investigated with X-ray diffraction, scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy to determine the microstructure, the interface chemistry and the surface chemistry of the various impregnated samples. The SDC nanoparticles cover the surface of the LSM-YSZ backbone to a large extent; they are approximately 5-20 nm in diameter and have a cubic crystal structure. Low concentrations of lanthanum and manganese originating from LSM were detected within SDC particles. It was also observed that the relative atomic concentration of strontium increased on the LSM-YSZ surface with increasing amount of SDC nanoparticles. These findings are related to the applied nanoparticle impregnation method. It is indicated that interactions between surfactant, nanoparticles, impregnation solution and the LSM-YSZ composite take place which can locally affect the surface and interface chemistry of the investigated materials.     

Chemomechanical properties and microstructural stability of nanocrystalline Pr-doped ceria: An in situ X-ray diffraction investigation

The chemomechanical properties and microstructural stability of nanocrystalline Pr_xCe_1 − xO_2 − δ solid solutions are studied as a function of temperature by in situ X-ray diffraction measurements under oxidizing conditions at P(O₂) ~ 200 mbar. The chemical expansion coefficient of nanocrystalline powder specimens, operative at intermediate temperatures during which Pr⁴⁺ is reduced to Pr³⁺, is found to be similar to that obtained for coarse-grained Pr_xCe_1 − xO_2 − δ. This is contrary to reports regarding variation of physical and chemical properties with crystallite size. The thermal expansion coefficient, measured under conditions for which Pr_xCe_1 − xO_2 − δ is highly oxygen deficient, was found to be greater than that measured for fully oxidized Pr_xCe_1 − xO_2 − δ, with potential sources of these changes discussed. Moreover, the microstructure of nanocrystalline Pr_xCe_1 − xO_2 − δ is observed to have excellent stability at working temperatures below 800 °C, enabled by the inherent microstrain in the structure, highlighting the potential application of this material for solid state electrochemical devices.     

Ce-Pt-Pd/不锈钢丝网催化剂的制备与催化性能

采用阳极氧化技术在不锈钢丝网上自生长了一层结构致密的阳极氧化膜,并以此为载体,制备出一种高活性、高稳定性的负载型Ce-Pt-Pd催化剂.考察了该系列催化剂对甲苯、丙酮和乙酸乙酯的氧化活性,并用扫描电镜、X射线光电子能谱和程序升温氧化技术对催化剂进行了表征.结果表明,不锈钢丝网载体表面自生长的氧化物膜十分有利于活性组分的负载,制得的催化剂具有较高的催化燃烧有机化合物的活性和稳定性.