Promising optimization of the CeO2/CeCl3 cycle by reductive dissolution of cerium(IV) oxide

Although thermochemical cycles could constitute a promising approach to large-scale hydrogen production, physicochemical studies have shown that they will be difficult to implement because of poor reactivity. Most cycles involve solid–gas systems in which the reactivity is limited by interface passivation processes. To mitigate this difficulty a new approach is described based on a preliminary study performed with the UT-3 cycle. Replacing bromine by chlorine and iron by cerium not only simplifies the cycle from four reactions to three, but also allows the use of much less hazardous reactants while ensuring greater theoretical energy efficiency than the UT-3 cycle. In the proposed new reaction architecture the cycle can be partially carried out in the aqueous phase by reductive dissolution of cerium(IV) oxides to cerium(III) chlorides in an azeotropic hydrochloric acid solution. This has many advantages and could be used to optimize the operating temperatures, enhance reaction progress by eliminating reaction products at the interface, enhance the reaction kinetics by eliminating the solid diffusion layers, systematically regenerate the reactants within the process itself, and also facilitate gas separation by differential solubility. The assessment also shows that photon activation by dissociation of chlorine radicals during the first step, the reverse Deacon reaction, could allow the first two reactions to occur at lower temperatures near 100 °C.     

Characterization of a zinc-cerium flow battery

The performance of a divided, parallel-plate zinc-cerium redox flow battery using methanesulfonic acid electrolytes was studied. Eight two and three-dimensional electrodes were tested under both constant current density and constant cell voltage discharge. Carbon felt and the three-dimensional platinised titanium mesh electrodes exhibited superior performance over the 2-dimensional electrodes. The charge and discharge characteristics of the redox flow battery were studied under different operating conditions and Zn/Ce reactant, as well as methansulfonic acid concentration. The cell performance improved at higher operating temperatures and faster electrolyte flow velocities. The number of possible cycles increased at reduced states of charge. During 15 min charge/discharge per cycle experiment, 57 cycles were obtained and the zinc reaction was found to be the limiting process during long term operation.     

Enhanced stability for preferential oxidation of CO in H2 under H2O and CO2 atmosphere through interaction between iridium and copper species

Preferential oxidation of CO (CO-PROX) is one of the most investigated methods for reducing residual CO in H₂-rich stream to acceptable level in proton exchange membrane fuel cells. However, development of catalyst with high stability under simulated practical conditions is still challenging. Herein, a series of Cu_xCe_1-xO₂ (x = 0, 0.05, 0.09, 0.17) supported Ir catalysts were prepared and 1 wt%Ir/Cu_0.09Ce_0.91O₂ exhibited full conversion of CO in a wide temperature window (80–180 °C), excellent stability and resistance to CO₂ and H₂O poison. Characterization results reveal that the superior performance was mainly associated with the interaction between Ir and Cu species, which resulted in that the adsorbed H₂O on Ir sites was activated to react with adsorbed CO on Cu sites to form easily decomposable bicarbonates and formate species instead of main intermediate of carbonates for 1 wt% Ir/CeO₂ and Cu_0.09Ce_0.91O₂. This work provides a new sight for developing high-performance heterogeneous catalysts.     

Photoluminescence and decay characteristics of cerium,gallium and vanadium - containing borate-based bioactive glass powders for bioimaging applications

Biomaterials having photoluminescent properties play a crucial role in real-time bioimaging after in vivo implantation. In this study, photoluminescence properties and decay characteristics of the borate-based 13–93B3 glasses containing different concentrations of cerium, gallium, and vanadium oxides were investigated for biomedical applications. The borate-based bioactive glass powders were prepared using melt-quench technique and size reduction was performed through planetary ball milling. Bioactivity of the prepared powders was investigated in simulated body fluid at 37 °C under static conditions. The photoluminescent properties and decay kinetics of the as-prepared and the SBF-treated bioactive glass powders were analyzed by steady-state and time-resolved photoluminescence measurements. Results revealed that the cerium activated glasses exhibited an intense luminescence centered at 538 nm. Broad-band emission of the gallium and vanadium doped samples was centered at 440 and 572 nm, respectively. All of the SBF-treated glasses exhibited enhanced lifetimes and bi-exponential decays both in nanosecond and microsecond regime measurements. It was concluded that depending on the dopant concentration, bioactive glass particles prepared in the study showed remarkable photoluminescence and have potential to be used in bioimaging applications.     

纳米颗粒氧化铈的制备研究

氧化铈由于具备独特的redox性能,在催化剂制备方面倍受关注。本文介绍了水热法、模板剂诱导均相沉淀法制备纳米颗粒氧化铈的合成工艺。在NaOH、NH3反应体系中,120℃、24h可获得肩峰较宽、具有CeO2、Ce3O3固溶峰的纳米结构氧化铈颗粒。粒径在5～15nm,比表面积为128 52m2/g;模板诱导沉淀法在(NH2)2CO为0 44mol、SDS为0 02mol、Ce(NO3)3·6H2O为0 01mol、反应72h,可制备出比表面积为155 08m2/g,粒径为10nm、孔径(poresize)为10 07nm的氧化铈。两种合成方法均可制备出具有催化剂所要求的、较高内比表面积和较好纳米结构相的氧化铈颗粒。     

Thermodynamic calculation method for formation of rare earth inclusions in conductive copper

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Cerium: a suitable green corrosion inhibitor for tinplate

In chloride solutions, tinplate exhibits localised corrosion processes due to the defects or imperfections of the outer Sn layer, which leaves the Sn-Fe alloyed layer exposed to aggressive solutions. The anodic character of the external Sn with respect to the internal alloyed layer, will lead to its dissolution acting as a sacrificial anode. The addition of cerium salts to the aggressive media decreases the pitting susceptibility of tinplate by means of cerium precipitation on the cathodic sites (bare Sn-Fe areas). This induces to a change of the controlling mechanism suggesting that cerium is a cathodic inhibitor for tinplate, which could be corroborated by removal selectively the outer Sn layer and leaving the Sn-Fe layer directly exposed to the solution. In these conditions, the corrosion process of the steel base will take place through the defects of the Sn-Fe layer, which presents a cathodic character in comparison to the base metal, inducing the precipitation of cerium on the alloyed layer.Scanning electron microscopy and energy dispersive spectroscopy analysis revealed that the location of cerium precipitates depend on the distribution of the cathodic areas that could lead either to a continuous layer covering the surface or to precipitates inside the mechanical failures.     

Controlled growth of Bi-Functional La doped CeO2 nanorods for photocatalytic H2 production and supercapacitor applications

The rapid increase in energy consumption has severely rehabilitated human life urging to develop reliable and environmental friendly energy storage devices. Target oriented, systematic approach has been adopted to synthesis La doped CeO₂ nanostructures with percentage as La_xCe_1-xO₂ (X = 0,1,3,5,7) for potential super capacitors applications. Morphological doping impact on H₂ production, electrochemical and optical properties are thoroughly investigated. XRD studies revealed the crystalline phase purity and attained approximately 35 nm average crystallite size. The SEM images exposed that primary morphology nano-particles has been tuned into nanorods by increasing the La concentration in CeO₂ with size range 40～60 nm. CV graphs depicted that the prepared electrodes obey the pseudo capacitive faradaic reactions behavior in nature. Maximum capacitance (925 F g^-1) has been achieved by La_0·05Ce_0·95O₂ which is better than numerous reported materials. The La_0·05Ce_0·95O₂ also exhibited excellent GCD stability with 87.8% retention exhibiting it suitability for supercapacitor applications. Furthermore, the La_0·05Ce_0·95O₂ showed the significantly higher H₂ (9 μmol h^?1g^?1) production rate as compared to undoped CeO₂ and La_0·01Ce_0·99O_2, La_0·03Ce_0·97O₂ samples. This higher production is attributed to the recombination rate and have strong substantial correlation with optical characteristics.     

Effect of surface properties controlled by Ce addition on CO2 methanation over Ni/Ce/Al2O3 catalyst

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.