Incorporation Of Ce Research Articles

Preferential oxidation of carbon monoxide in simulated reformatted gas over PtAu/Ce xZn yO 2 catalysts

A series of Pt–Au catalysts prepared by co-precipitation (CP) and single step sol-gel (SSG) methods was investigated for selective CO oxidation. The characteristics of the prepared catalysts were determined by XRD, BET surface area, SEM, H 2-TPR, chemisorption analysis, and FTIR. The simulated reformatted gas consisted of 1% CO, 1% O 2, 0% to 10% H 2O, 0–20% CO 2, and 40% H 2 in He balance. The operating temperature range was varied from 50 °C to 190 °C at atmospheric pressure. The experimental results elucidated that the catalytic preparation method had a significant effect on the catalyst characteristics and its activity. The catalytic performance over PtAu/Ce 1Zn 1O 2 prepared by co-precipitation was higher than that of PtAu/CeO 2 and PtAu/ZnO because of the incorporation of Ce 4+ ions and the Zn 2+ ions in the lattice. To encourage better catalytic performance, the catalysts should be calcined at 500 °C for 5 h and pretreated in a H 2 atmosphere. The CO conversion for the single- and double-stage reaction was reduced when adding water vapor and CO 2 to the feedstream; the water vapor and CO 2 molecules compete for the adsorption with CO on the active sites of the catalysts. During the deactivation test for 60 h, the CO conversion and selectivity are maintained.

Ce Doped-GeSbTe Thin Films Applied to Phase-change Random Access Memory Devices

AbstractA study on microstructure and electrical property of cerium (Ce)-doped Ge2Sb2Te5 (GST) layers for phase-change memory (PCM) application were presented. Ce doping does not suppress the resistivity of amorphous GST and the resistivity ratio of amorphous and crystalline GST remains at about 105. Further, Ce-doping escalates the recrystallization temperature (Tx) of GST from 159 to 236°C. Such a unique behavior would greatly benefit the preservation of signal contrast as well as the high-density signal storage and will not cause the increase of device writing current. X-ray diffraction (XRD) indicated that Ce doping stabilizes amorphous GST and suppresses the formation of hexagonal phase. Transmission electron microscopy (TEM) revealed Ce doping refines the grain size of GST. Kissinger's analysis found that Tx and activation energy (Ea) of phase transition for doped-GST both increase with the increase of Ce content. Isothermal experiment found the Ce doping increases temperature for 10-yr data retention from 76 and 170°C. This is attributed to the presence of Ce solutes in GST matrix that inhibits the grain growth during recrystallization.Static-mode electrical test on PCM device containing doped GST as the programming layer found that Ce incorporation indeed increases the switching threshold voltage (Vth). This confirmed that Ce doping effectively retards the crystallization of GST and improves the stability of amorphous GST.

Synergistic inhibition effect of rare earth cerium(IV) ion and sodium oleate on the corrosion of cold rolled steel in phosphoric acid solution

The synergistic inhibition effect of rare earth cerium(IV) ion (Ce 4+) and sodium oleate (SO) on the corrosion of cold rolled steel (CRS) in 3.0 M phosphoric acid (H 3PO 4) has been investigated by weight loss, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and scanning electron microscope (SEM) methods. The results reveal that SO has a moderate inhibitive effect and its adsorption obeys Temkin adsorption isotherm. Ce 4+ has a poor effect. However, incorporation of Ce 4+ with SO improves the inhibition performance significantly, and exhibits synergistic inhibition effect. SO acts as a cathodic inhibitor, while SO/Ce 4+ mixture acts as a mixed-type inhibitor.

Growth of LGSO: Ce crystals by the Czochralski method

Single crystals of Lu2xGd2 − 2xSiO5: Ce (0 < x < 1) compounds with different atomic ratios Lu/(Lu + Gd) have been grown by the Czochralski method. It has been shown that a change in the spatial symmetry from P21/c to C2/c in the course of substitution of lutetium for gadolinium occurs at the ratio Lu/(Lu + Gd) = 0.1. The lattice thus formed with symmetry C2/c in the structure of Lu2xGd2 − 2xSiO5: Ce crystals favors the maximum possible incorporation of Ce3+ ions into the sevenfold-coordinated position with respect to oxygen. This explains the substantial improvement of the scintillation characteristics of the grown crystals.

Development of high-performance cathodes for IT-SOFCs through beneficial interfacial reactions

We propose a new way to develop high-performance cathodes for IT-SOFCs by utilizing the interfacial reactions. SrCoO x was selected as the starting electrode material, which took a vacancy-ordered 2H BaNiO 3-type structure and showed negligible ionic conductivity and low electrical conductivity. Phase reactions between SrCoO x and Sm 0.2Ce 0.8O 1.9 happened at 900 °C or higher, resulting in the incorporation of Sm and Ce into its lattice structure. This promoted the phase transition to a cubic perovskite and led to substantial increase in the electrical conductivity and oxygen mobility of the electrode. By utilizing such phase reactions, the SrCoO x + Sm 0.2Ce 0.8O 1.9 composite was developed into a high performance electrode with a low area specific resistance of 0.08 Ω cm −2 at 650 °C. An anode-supported cell with such electrode delivered a peak power density of 795 mW cm −2 at 600 °C.

Synergistic inhibition effect of rare earth cerium(IV) ion and 3,4-dihydroxybenzaldehye on the corrosion of cold rolled steel in H 2SO 4 solution

The synergistic inhibition effect of rare earth cerium(IV) ion and 3,4-dihydroxybenzaldehye (DHBA) on corrosion of cold rolled steel (CRS) in H 2SO 4 solution was first investigated by weight loss and potentiodynamic polarization methods. Effects of inhibitor concentration, temperature, immersion time and acid concentration on synergism are discussed in detail. The results reveal that DHBA has moderate inhibitive effect and its adsorption obeys Temkin adsorption isotherm. For the cerium(IV) ion, it has negligible effect. However, incorporation of Ce 4+ with DHBA improves the inhibition performance significantly, and produces strong synergistic inhibition effect.

Enhancement of long-persistence by Ce3+ co-doping in Sr2MgSi2O7:Eu2+, Dy3+ blue phosphor

Sr2MgSi2O7:Ce3+, Sr2MgSi2O7:Eu2+, Sr2MgSi2O7:Eu2+, Ce3+, Sr2MgSi2O7:Eu2+,Dy3+ and Sr2MgSi2O7: Eu2+, Dy3+, Ce3+ were prepared under a weak reducing atmosphere by a solid state reaction. Ce3+ singly doped sample had no afterglow. Sr2MgSi2O7:Eu2+, Ce3+showed some afterglow with a short persistenence. By incorporation of Ce3+, an efficient energy transfer from Ce3+ to Eu2+ was found and emission intensity of Eu2+ was enhanced. The triply doped phosphor Sr2MgSi2O7: Eu2+, Dy3+, Ce3+ has higher brightness and longer lasting time than Sr2MgSi2O7:Eu2+, Dy3+.

Synergism between rare earth cerium(IV) ion and vanillin on the corrosion of cold rolled steel in 1.0 M HCl solution

The synergism between rare earth cerium(IV) ion and vanillin on the corrosion of cold rolled steel (CRS) in 1.0 M HCl solution was first investigated by weight loss, potentiodynamic polarization, ultraviolet and visible spectrophotometer (UV–vis), X-ray photoelectron spectroscopy (XPS) and atomic force microscope (AFM). The results revealed that vanillin had a moderate inhibitive effect, and the adsorption of vanillin obeyed the Temkin adsorption isotherm. For rare earth Ce 4+, it had a negligible effect. However, incorporation of Ce 4+ with vanillin significantly improved the inhibition performance, and produced strong synergistic inhibition effect. Depending on the results, the synergism mechanism was proposed.

Enhanced ferroelectric properties of Ce-substituted BiFeO 3 thin films on LaNiO 3/Si substrates prepared by sol–gel process

The effects of Ce substitution on the structural and electrical properties of multiferroic BiFeO 3 thin films grown on LaNiO 3/Si(1 0 0) substrates by a sol–gel process have been reported. X-ray diffraction data confirmed the substitutions of Ce into the Bi site with the elimination of all secondary phases under a substitution ratio x = 15%. The dielectric constants of the films increased from 90 to ∼260 below 100 kHz with 5% molar Ce substitution and the films showed enhanced dielectric behavior. We observed a substantial increase in the remnant polarization ( P r) with Ce substitution and obtained a maximum value of ∼71 μC/cm 2 by 5% molar Ce incorporation. The leakage current behavior at room temperature of the films was studied and it was found that the leakage current density decreased from 10 −6 to 10 −8 A/cm 2 for 5% molar Ce-substituted films under a field 150 kV/cm. The reduction of dc leakage current of Ce-substituted films is explained on the basis of relative phase stability and improved microstructure of the material.

Schottky emission in nanoscopically crystallized Ce-doped SnO 2 thin films deposited by sol–gel-dip-coating

This paper reports the electrical effects of the incorporation of Ce(III) or Ce(IV) in SnO 2 thin films, prepared by the sol–gel-dip-coating technique. This doping has drastically increased the resistivity compared to undoped thin films. Nanoscopic dimension of crystallites, in the range 5–10 nm, contributes to this increase. The high number of crystallites decreases the mobility due to the increase of the density of potential barrier between grains per unit of volume. High doping leads to low conductivity when Ce(III) salt is used as precursor, which assures the acceptor-like nature of this ion in the matrix. Current as function of voltage, measured for several temperatures, leads to the predominance of Schottky conduction mechanism, even though a tunneling process seems to be a good approximation for the observed deviations at lower applied electric fields. The potential barrier for Schottky emission is in the range 0.6–0.8 eV. For Ce(IV) doping, an increase of the grain boundary depletion layer seems to be responsible for the observed high resistivity, because it leads to higher electron scattering at grain boundary. Measurements done under room atmosphere lead to a higher barrier height than measurement done under vacuum conditions, due to oxygen adsorption at particles surface. For temperatures higher than 150 °C, under vacuum conditions, the elimination of O 2 − species becomes probable, increasing considerably the current density.

Synergistic inhibition effect of rare earth cerium(IV) ion and anionic surfactant on the corrosion of cold rolled steel in H 2SO 4 solution

The synergistic inhibition effect of rare earth cerium(IV) ion and anionic surfactant of sodium oleate (C 17H 33–COONa, SO) on the corrosion of cold rolled steel (CRS) in H 2SO 4 solution was first investigated by weight loss and potentiodynamic polarization methods. The results revealed that SO had a moderate inhibitive effect, and the adsorption of SO obeyed the Freundlich adsorption isotherm. For the cerium(IV) ion, it had a negligible effect. However, incorporation of Ce 4+ with SO significantly improved the inhibition performance, and produced strong synergistic inhibition effect. Depending on the results, the synergism mechanism was proposed.

Reactivity between La(Sr)FeO 3 cathode, doped CeO 2 interlayer and yttria-stabilized zirconia electrolyte for solid oxide fuel cell applications

Detailed X-ray diffraction (XRD) analysis of two different Sr-doped LaFeO 3 cathodes, YSZ electrolyte and two Sm/Gd-doped CeO 2 interlayer and their mixtures were used to evaluate the formation of undesired secondary reaction compounds. The analysis of room temperature X-ray diffraction data of the mixtures indicates the crystallization of strontium and/or lanthanum zirconates between the cathode and the electrolyte materials and no detected reaction between the cathode and the interlayer materials. For all the ferrite mixtures a significant shift in the diffraction peaks is observed, which is the result of the unit cell volume expansion and contraction of the cathode (LSF) structures mixed with electrolyte (YSZ), and with interlayers (SDC, GDC), respectively. On the other hand, a complete solid solution was observed between the crystal structures of YSZ electrolyte and SDC or GDC interlayers. The observed cell modifications for the ferrite mixtures were the result of the incorporation of Zr and Ce, in the B and A type positions of the perovskite structure, respectively. The electrolyte/interlayer interface shows the presence of intermediate compositions at high temperature. The electrochemical studies show better results when a Sm-doped CeO 2 is inserted between the cathode and electrolyte material. The best result obtained is for the half-cell prepared with LSF-40 and SDC interlayer on YSZ electrolyte.

H2S photodegradation by TiO2/M-MCM-41 (M = Cr or Ce): Deactivation and by-product generation under UV-A and visible light

M-MCM-41 molecular sieves (M=Ce or Cr) were prepared by a hydrothermal method and impregnated with TiO2. The materials were characterized by XRD, N2 adsorption–desorption, DRS and XPS. Their potential application to photooxidize H2S in a wet gas stream was tested in a continuous flow reactor operating at a flow rate of 110mLmin−1 at 50% relative humidity and using 30ppmv of the pollutant. The photocatalytic efficiency using UV-A and visible light was compared to the activity of TiO2/MCM-41 without heteroatoms incorporated into the MCM-41 structure. It was found that the incorporation of Ce did not improve the performance of TiO2/MCM-41, but Cr-containing samples presented higher initial efficiency and were able to photooxidize H2S without formation of SO2 as a by-product, in contrast to the other prepared samples and to Degussa P-25 TiO2. Moreover, no other gaseous by-product was detected. The isomorphic incorporation of Cr into the structure of MCM-41 followed by TiO2 incorporation produced photocatalysts that presented good adsorption capacity and were much more active under visible light than under UV-light. This performance represents an important advantage for solar applications. Their photoactivity depended on the concentration of chromium; the highest efficiency was attained with samples with a Si/Cr ratio of 50. Finally, deactivation was observed as a consequence of sulfate accumulation on the surface of the catalyst and reduction of Cr6+.

Carbon dioxide hydrogenation over Fe–Ce catalysts

Unpromoted and Ce-promoted Fe catalysts were tested in the CO 2 hydrogenation reaction. Both catalysts form predominantly CO and hydrocarbons (C 1 –C 10 ). Reaction rate and selectivity to the different products were essentially the same with both catalysts. The chain growth probability ( α ) was very similar in both cases (∼0.44). Prior of being used in the CO 2 hydrogenation reaction, the catalysts were used in CO hydrogenation until the stationary state was established. It was found that the Ce incorporation into the iron catalyst does not alter its final performance but it shortens the time required to reach stationary-state operation conditions.

Synergism between rare earth cerium(IV) ion and vanillin on the corrosion of steel in H 2SO 4 solution: Weight loss, electrochemical, UV–vis, FTIR, XPS, and AFM approaches

The synergism between rare earth cerium(IV) ion and vanillin (4-hydroxy-3-methoxy-benzaldehyde) on the corrosion of cold rolled steel (CRS) in 1.0 M H 2SO 4 solution at five temperatures ranging from 20 to 60 °C was first studied by weight loss and potentiodynamic polarization methods. The inhibited solutions were analyzed by ultraviolet and visible spectrophotometer (UV–vis). The adsorbed film of CRS surface containing optimum doses of the blends Ce 4+–vanillin was investigated by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and atomic force microscope (AFM). The results revealed that vanillin had a moderate inhibitive effect, and the inhibition efficiency (IE) increased with the vanillin concentration. The adsorption of vanillin obeyed Temkin adsorption isotherm. Polarization curves showed that vanillin was a mixed-type inhibitor in sulfuric acid, while prominently inhibited the cathodic reaction. For the cerium(IV) ion, it had a negligible effect, and the maximum IE was only about 20%. However, incorporation of Ce 4+ with vanillin improved significantly the inhibition performance. The IE for Ce 4+ in combination with vanillin was higher than the summation of IE for single Ce 4+ and single vanillin, which was synergism in nature. A high inhibition efficiency, 98% was obtained by a mixture of 25–200 mg l −1 vanillin and 300–475 mg l −1 Ce 4+. UV–vis showed that the new complex of Ce 4+–vanillin was formed in 1.0 M H 2SO 4 for Ce 4+ combination with vanillin. Polarization studies showed that the complex of Ce 4+–vanillin acted as a mixed-type inhibitor, which drastically inhibits both anodic and cathodic reactions. FTIR and XPS revealed that a protective film formed in the presence of both vanillin and Ce 4+ was composed of cerium oxide and the complex of Ce 4+–vanillin. The synergism between Ce 4+ and vanillin could also be evidenced by AFM images. Depending on the results, the synergism mechanism was discussed from the viewpoint of adsorption theory.

Effects of surfactant/silica and silica/cerium ratios on the characteristics of mesoporous Ce-MCM-41

Using the surfactant CTMABr (cetyltrimethyl ammonium bromide) and cerium(IV) sulfate, mesoporous Ce-MCM-41 molecular sieves were produced under a hydrothermal condition with various surfactant/silica (surfactant/Si) and silica/cerium (Si/Ce) ratios. Changes to the structural traits caused by changing the molar ratios of both surfactant/Si and Si/Ce were investigated. XRD (X-ray diffraction), FT-IR (fourier transform infrared spectroscopy), and SEM (scanning electro microscopy) were used for the characterization of prepared mesoporous samples. Among the tested molar ratios, surfactant/Si ratio of 0.5 and 0.2 showed highest values of d 1 0 0 and intensity, respectively, for the Si-MCM-41. XRD analysis also identified a quintessential hexagonal structure of Ce-MCM-41 for the Si/Ce molar ratio higher than 40 (maintaining the surfactant/Si ratio at 0.2). When cerium content was increased to have the Si/Ce molar ratio of 20, the hexagonal structure of Ce-MCM-41 was collapsed due to the structural stress of substituted cerium. FT-IR results confirmed calcination of Ce-MCM-41 and the incorporation of Ce 4+ ions of cerium sulfate into the silica surface with proper removal of the surfactant. Rod-like shape with rounded edges of the prepared Ce-MCM-41 samples was identified by SEM. These results suggest surfactant/Si ratio of 0.2 and Si/Ce ratio of 40 for the production of Ce-MCM-41 with the highest level of crystallinity.

Redshift of Green Photoluminescence of Ca3Sc2Si3O12 : Ce3 + Phosphor by Charge Compensatory Additives

The luminescence wavelength of , which is a green-emitting phosphor under blue light excitation, was moved toward longer wavelength by addition of Mg. This modification is very valuable for commercial applications because it increases the brightness of the phosphor by increasing the overlap with the visibility curve. Magnesium is likely incorporated into the Sc position of the host crystal because the ionic radius of Mg is close to that of Sc. The substitution probably compensates for the excess positive charge induced by incorporation of Ce into the Ca position. The content of Ce in the host crystal was increased by increasing the amount of Mg in the raw material mixture; the inverse relationship was also observed. The spectral shift was also observed by adding Na or Li, which probably substituted the Ca position and compensated the excess charge induced by Ce in the Ca position. The change in luminescence spectra occurred irrespective of the type of charge compensatory additive used. Therefore, the spectral modification was mainly due to the increase in activator. Modification of the luminescence decay characteristics by the additives was also examined. The decay curve of the phosphor containing Mg showed a nonexponential profile.

Low Cost, Ceria Promoted Perovskite Type Catalysts for Diesel Soot Oxidation

Perovskite type catalysts with SrCoO3 and Sr0.8Ce0.2CoO3 compositions have been prepared by co-precipitation and other methods and, their catalytic activity towards diesel particulate matter (PM)/carbon oxidation has been evaluated under the loose contact con- dition. These catalysts show excellent catalytic activity for PM/carbon oxidation, despite their low surface area and under the loose contact condition. The synergistic effects of Ce incorporation in perovskite and presence of a small amount of potassium appears to be responsible for the high soot oxidation activity of these perovskite type materials. The Ce incorporation seems to be contributing by enhancing the redox property of the catalyst, while it appears unlikely that potassium is contributing by improving the catalyst-soot contact through its volatiza- tion. The catalysts show excellent thermal stability and stable activity under repeated cycles of use.

Evolution of corrosion protection for sol–gel coatings doped with inorganic inhibitors

One the way to improve the self-repair properties of sol–gel films on aluminium alloy is the addition of corrosion inhibitors which could be released from the coating, minimising the corrosion of the unprotected area. Environmentally friendly corrosion inhibitors are studied (chromium III, molybdate, permanganate and cerium III) and compared to the standard corrosion inhibitor, i.e. hexavalent chromium. Corrosion performances are studied by polarisation resistance (Rp) in chloride medium. Evolution of composition of sol–gel coatings, during the corrosion test, is examined by GDOES (glow discharge optical emission spectroscopy). The results show that the morphology of sol–gel and the solubility of the additive play a role in the effectiveness of corrosion protection for a long term. Additives such as molybdate and permanganate ions decrease the sol–gel network stability and are too soluble (they are rapidly lost from the sol–gel films, in an aggressive medium), decreasing the power to prevent corrosion. Incorporation of Ce III is not efficient for a long time due to its high solubility. Sol–gel films containing Cr VI and Cr III provide adequate corrosion protection, due to the sol–gel stability and their low solubility.

The use of a soaking procedure combined with the sintering process to reach a high cerium content in a cerium-bearing Y-britholite

A Y-britholite loaded with Ce, with the chemical composition (19.12% SiO 2, 7.53% P 2O 5, 15.87% CaO, 46.77% Y 2O 3, 0.67% CaF 2, 0.95% H 2O, 9.09% CeO 2) was synthesized by two methods: a dry route and a combined route of natural sintering/soaking procedure. In the first synthesis method, all the milled reagents are pressed in pellets at 340 MPa and then sintered for 20 h in air at 1473 K. In the second method, the Ce-free mineral was first obtained by the dry route described above. Then, it was unfiltered by a cerium nitrate solution to incorporate Ce in the Y-britholite crystalline structure. The powder is calcined at 1223 K and sintered in air at 1473 K for 20 h. These last two steps are repeated twice to allow a good incorporation of Ce in the material, as well as reaching a good homogeneity of the mineral. A physical characterization of the materials coming from the two synthesis methods, by both XRD and EDX analyses, gives a total Ce incorporation into the mineral obtained by the combined dry/wet synthesis process, namely 7.40 wt.%, against a 5 wt.% of Ce incorporation rate in the Y-britholite obtained by the dry route process. The XRD analysis identified crystalline phases were a major hexagonal crystalline phase of Y-britholite in both Y-britholites. To assess the chemical durability of the synthesized minerals, a water static leach test was performed at 298 K for the dry way obtained Y-britholite, and at 298, 323 and 363 K for the dry/wet way obtained Y-britholite. The tests were based on the release of cerium in water. UV analysis was used to follow the evolution of Ce concentrations in the leachates. The Ce mean diffusion coefficients were of the order of magnitude of 10 −7 m 2 s −1, and the mineral water altered layers were lower than 220 μm (22 × 10 −5 m). This demonstrated the superficial phenomenon of leaching. The diffusional model of leaching was validated, proving the chemical durability of the mineral, even at high leaching temperatures for the dry/wet way obtained Y-britholite. This synthesis method has proved the possibility to confine higher amounts of Ce, an actinide surrogate, into the crystal of Y-britholite, with the combined synthesis method of sintering/soaking procedure, compared with the dry route of synthesis.