Lanthanum Cerium Oxide Research Articles

Influence of the La/Ce ratio on La-Ce oxides promoted by Sr in the methane oxidative coupling reaction

The high methane availability and its significant role as a greenhouse gas have led the scientific community to pursue methods for its use. This paper proposes the usage of the oxidative coupling of methane (OCM) as a promising path to transform methane directly into value-added hydrocarbons, mostly ethylene, which serves as a crucial compound in the petrochemical sector. An efficient OCM catalyst should contain substantial basicity and oxygen vacancies for providing surface electrophilic oxygen species, such as superoxides and peroxides, instrumental for boosting selectivity towards C2 products. Mixed lanthanum-cerium oxide (La-Ce) catalysts have emerged as strong candidates in OCM due to their high thermal stability, oxygen mobility, and high alkalinity. In this study, they were prepared through a surfactant-assisted hydrothermal method with different La/Ce ratios for fine-tuning their basic properties and promoting oxygen mobility on the surface of the catalysts. Samples followed a volcano-shaped relationship between C2 yield and La content, with optimal performance at a La/Ce molar ratio of 2.1, attributed to the interplay between the high amount of basic sites and oxygen vacancies, increasing the presence of superoxide species over lattice oxygen. Moreover, the Sr-promoted catalyst showed high density of strong basic sites while preserving the reactive oxygen species, achieving 20 % CH4 conversion, with 57 % C2 compounds selectivity at 750 °C and GHSV of 18.000 mL.gcat−1.h−1.

Metal-organic decomposed lanthanum cerium oxide thin films: A study of chemical and surface properties

Lanthanum cerium oxide thin films have been deposited on n-type (100) silicon wafers using the spin coating technique. The post-deposition annealing was performed over spin-coated films. The compositional studies were conducted by performing Fourier transform infrared spectroscopy, Energy dispersive X-ray spectroscopy, and X-ray diffraction. Ellipsometry was used to determine the thickness and atomic force microscopy was performed to understand the surface morphology of the deposited thin films. The effect of rapid thermal annealing at different temperatures over the structural and chemical properties of the LaCeO2 thin films was observed. The FTIR spectra show the formation of silicates at the interface of the oxide and semiconductor, while XRD results show that the films become crystalline with increased annealing temperature. The refractive index was observed to be reduced with an increase in the annealing temperature and a minor reduction in the physical thickness as per the sample standard deviation of 0.2981[Formula: see text]nm.

Study on the thermal insulation property of lanthanum–cerium oxide coatings

Functional fillers with low thermal conductivity and high near-infrared reflectance play a vital role in high temperature thermal insulation coatings and make an outstanding contribution to achieving efficient comprehensive thermal insulation. In this work, the thermal insulation and bonding properties of lanthanum–cerium oxide (LCO) coatings were regulated by composition design. The effects of the La/Ce mole ratio on phase composition, the thermal conductivity and near-infrared reflectivity of LCO coatings were investigated systematically. The results showed that coating with a La/Ce mole ratio of 1:1 possess the excellent thermal insulation properties (ΔT ≈ 115°C) due to the formation of a LCO solid solution and a lanthanum phosphate mesophase with low thermal conductivity and high near-infrared reflectivity. In addition, the mortise and tenon structure was formed between the coating and the substrate, which led to the remarkable bonding properties. The LCO coating offers excellent thermal insulation properties and broad application prospects in the fields of high temperature and energy conservation.

Phase stability and initial phase high-temperature corrosion behavior of non-stoichiometric lanthanum cerium oxide thermal barrier coatings

Three different compositions of lanthanum cerium oxide thermal barrier coatings with varied cerium oxide (1.8CeO2, 1.9CeO2 and 2.0CeO2) compositions were synthesized and plasma sprayed to achieve free-standing coatings. The phase stability studies showed that the coatings are stable at 1400 °C after 100 h. The high-temperature corrosion was performed in the presence of sulfate-vanadate (50 wt%Na2SO4+50 wt%V2O5) at 1000 °C for 4 h. The result depicts LaVO4 as the major corrosive product formed in all three compositions along with CeVO4, LaCeVO4 and CeO2. The hot corrosion test result gives information that the composition of CeO2 greatly influences the hot corrosion resistance. The increase in CeO2 percentage increases the resistance against the infiltration of molten sulfate-vanadate compounds. This investigation provides a feasible way to understand the coating composition for better hot corrosion resistance in sulfate-vanadate mixtures.

Single-step methane to methanol over lanthanum cerium oxide: The crucial role of surface reactive oxygen and carbonate species

The single-step conversion of methane to methanol (MTM) represents an attractive route for the valorization of low-concentration coalbed methane (CBM). In this work, the effects of surface reactive oxygen and carbonate species on the catalytic performance of LaCeOx materials for MTM reaction was investigated. Lanthanum cerium oxide with different crystal structure were prepared by adjusting the ratio of La to Ce. Under low methane concentration (8 vol.%), La5Ce1 sample with defective fluorite phase exhibited the best methanol site-time yield to 20 μmol gcat−1h−1. The more oxygen vacancies on defective fluorite phase promote the generation of reactive oxygen species. Moreover, it was also found that the incorporation of Ce weakened the adsorption of surface carbonate. The more moderately adsorbed carbonate on La2Ce1 sample enhanced the methanol selectivity. In-situ diffuse reflectance Fourier transform infrared spectroscopy (In-situ DRIFTS) further revealed the different methane to methanol pathway over La5Ce1 and La2Ce1 sample. Reactive oxygen species were attributed to the site for methane activation and CH3O* was the intermediate group of methanol. This study provides a new point that the oxygen species of lanthanum-cerium oxide could be regulated to promote their performance for MTM reaction, and we believed that the as-discussed oxide could be employed as the host materials for active phases as well.

Blocking effect in Nb-engineered high-entropy oxides with strengthened grain boundary corrosion resistance

Lanthanum-cerium oxide derived high-entropy ceramics have been verified to be promising thermal barrier coatings (TBCs) materials for the protection of hot-end components in high-performance aero-engines/gas turbines. However, the dissatisfactory hot corrosion resistance of TBCs to Na2SO4 + V2O5 molten salt from fuel exhaust is identified as a crucial bottleneck. Herein, a stabilization element Nb is introduced into typical high-entropy cerates to strengthen the corrosion resistance. When corroded, it favors an intermittent generation of spindle-shaped corrosion products at grain boundary and effectively blocks the further penetration of corrosion medium. Compared with other constituent elements, Nb in the as-designed material presents a weak adsorption energy (-0.43 eV) with the final reaction intermediate of corrosion medium (VO43-). It yields an anchoring effect to stabilize the pristine crystal structure. What’s more, the differential charge density of Ce is highly influenced by Nb, leading to a strong interaction with VO43-. With Ce tightly adsorbed around the corrosion products, it cooperatively hinders the further infiltration of molten salts. These findings provide an interesting insight into the rational design of superior corrosion-resistant high-entropy TBCs.

Effect of lanthanum content on the thermophysical properties and near-infrared reflection properties of lanthanum-cerium oxides

A series of lanthanum-cerium oxides with different lanthanum content were synthesized by low-temperature solid-state method, and the effect of lanthanum content on the thermal conductivity and near-infrared reflectance of lanthanum-cerium oxide ceramics was systematically investigated. The results indicated that the thermal conductivity of lanthanum-cerium oxide ceramics decreased significantly with the increase of lanthanum content, which was mainly due to the non-negligible phonon scattering caused by the increased point defects in the structure. Lanthanum-cerium oxide ceramics with different lanthanum content had high near-infrared reflectivity (82%) between 1200 and 2200 nm. The lanthanum-cerium oxide ceramics prepared in this work has lower thermal conductivity and higher near-infrared reflectivity, which has broad application prospects in the field of high-temperature energy saving as thermal insulation material.

Hot corrosion properties of plasma sprayed La2Ce2O7/YSZ vis-à-vis La2Ce2O7/cluster paired zirconia thermal barrier coatings

Bilayered thermal barrier topcoats have lead to a remarkable breakthrough in overcoming the disadvantages of the conventional yttria stabilized zirconia (YSZ) thermal barrier coatings (TBCs). The present work is devoted to studying the hot corrosion properties of two different bilayered ceramic topcoats, viz., (i) lanthanum cerium oxide with the formula La2Ce2O7 (LCO)/YSZ and LCO/cluster paired zirconia (gadolinia, dysprosia and yttria stabilized zirconia -(Gd,Dy,Y)SZ) plasma sprayed TBCs. Plasma spray grade YSZ and (Gd,Dy,Y)SZ are prepared by co-precipitation and solution combustion techniques as reported in the literature. The effect of thickness of the plasma sprayed top LCO layer in bilayered LCO/YSZ and LCO/(Gd,Dy,Y)SZ TBC systems under Type I hot corrosion condition is examined. The LCO/(Gd,Dy,Y)SZ bilayered coating with 100 μm LCO thickness exhibits better hot corrosion resistance than the LCO/YSZ system. The phase transformation of t′-ZrO2 to m-ZrO2 in LCO/(Gd,Dy,Y)SZ (100/150 μm) TBC is reduced markedly (60%) compared to LCO/YSZ (100/150 μm) TBC.

Investigation of Microwave and Thermal Processing of Electrode Material of End-of-Life Ni-MH Battery

Ni-metal hydride (NiMH) batteries should be recycled, as they contain base metals (Ni, Co) and rare earth elements (La, Ce). In this study, thermal and microwave treatments are investigated as a pre-treatment method for decomposing electrode material (Ni(OH)2 and LaNi5). The kinetic analysis of thermal decomposition electrode material yields the activation energy of 41.3 kJ/mol. The maximum percentage of lanthanum nickel oxide phase and cerium oxide phase is obtained at 1000°C of thermal treatment and 15 min of microwave exposure. The formation of melted balls of Ni and its oxide (Ni ~ 72.8%) was observed in microwave exposure, and the tendency of ball formation decreased with increasing exposure time. The effect of microwave exposure and thermal treatment on the acid leaching (1 M HCl, at S/L-1:20, at 70°C for 2 h) was studied. The leaching results showed NiO and CeO2 phases in the leach residue of thermal and microwave treated products.

Oxidation Resistance of Plasma-Sprayed Double-Layered LC/YSZ Coatings with Different Thickness Ratios at High Temperatures

This study aims to enhance the oxidation resistance of ceramic coatings through designing and optimizing microstructure. A series of double-layered lanthanum–cerium oxide (LC) and 8 wt% yttria-partially-stabilized zirconia (YSZ) coatings with different thickness ratios were tailored. The isothermal oxidation experiment and molecular dynamics simulation results suggested that due to the lower oxygen ionic diffusion coefficient, double-layered LC/YSZ coatings exhibited an excellent antioxidation property compared to the single-layer YSZ coating. However, with the increase of LC layer thickness in LC/YSZ coatings, sintering-induced vertical cracks were easily formed within LC layer, which significantly shortened the oxidation resistance of LC/YSZ coatings by a burner rig test at 1225 °C. The equivalent thermal growth oxide thickness manifested that the optimum thickness ratio between LC and YSZ layers was 1:2.

Improving the thermal shock resistance and fracture toughness of synthesized La2Ce2O7 thermal barrier coatings through formation of La2Ce2O7/YSZ composite coating via air plasma spraying

Due to the substantial brittleness of the thermal sprayed coatings, fracture mechanic can effectively illustrate the applicability of such surface layers. Lanthanum-cerium oxide (LC) coatings usually show poor thermal sock behavior even at low temperatures, mainly induced by their low fracture toughness and decreased coefficient of thermal expansion. At the first step, this study deals with the solid state synthesis of LC. At the next step, the synthesized LC and YSZ used to apply composite coatings (monolithic LC, 75 wt% LC-25 wt% YSZ, 50 wt% LC-50 wt% YSZ, 25 wt% LC-75 wt% YSZ and monolithic YSZ) through thermal spray method. The fracture toughness and thermal shock resistance of the formed coatings were then investigated. X-ray diffraction spectroscopy, energy dispersive spectroscopy and field emission scanning electron microscopy were used to study the phase analysis, chemical composition and morphological investigations of the coatings, respectively. Results indicated that higher fraction of YSZ can lead to enhanced fracture toughness due to higher energy relieving rate. The best thermal shock resistance outcome was also achieved in LC-50 wt% YSZ composite coating, as the coating tolerated 350 thermal cycles.

High-k LaxCeyOz for Passivation of Si Substrate

High dielectric constant rare earth lanthanum cerium oxide (LaxCeyOz) films have been studied as the passivation layers for silicon substrate. Effects of post-deposition annealing time (15, 30, and 45 min) at 700°C towards capacitance-voltage characteristics of the films were investigated. As the annealing time was increased from 15 to 45 min, negative flatband voltage shift was observed, signifying the presence of positive charges in the samples. Interface trap density value calculated for the samples has shown to be the lowest for the film annealed for 45 min, owing to the presence of silicate interfacial layer to improve the overall interfacial quality.

Post-deposition-annealed lanthanum-doped cerium oxide thin films: structural and electrical properties

The metal-organic-decomposed lanthanum cerium oxide (LaCeO2) solution was spin-coated on p-type Si substrate to form thin films. The method of microwave-assisted annealing was adopted to modify the surface properties of the deposited thin films. The post-deposition annealing (PDA) at different microwave powers and thermal annealing temperature of 400 °C was performed on LaCeO2 thin films spin-coated on Si. Influence of this PDA on structural and electrical properties of deposited LaCeO2 thin films was studied and compared. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) results reveal the great improvement in the structural properties in terms of removal of residual impurities from LaCeO2 films, reduced roughness and improvement in crystalline properties as compared to those of hot-plate-annealed samples. The electrical properties of Al/LaCeO2/Si stack were also studied. The different electrical parameters such as k value, interface trap density (Dit) and effective oxide charges (Qeff) were extracted and found to be improved with the increase in microwave annealing power.

Effect of Metal Content on Ethanol Decomposition over Ni-Co Catalysts Supported on La-Ce Oxides.

The search for catalysts with features that can improve coke resistance and decrease byproduct formation is a current goal in H2 production from renewable sources. In this work, the effect of the presence of Ni nanoparticles over Co/La-Ce oxides on the ethanol decomposition reaction was studied. Catalysts were synthetized using as precursor a La0.8Ce0.2NixCo1-xO3 perovskite-type material to ensure a low segregation of phases and a high dispersion of metals. After reduction at 873 K, the perovskite structure was destroyed, and metal Co-Ni particles were supported over a lanthanum-cerium oxide. The materials were characterized by different techniques before and after reaction. Solids exhibited metal particle sizes between 5 and 15 nm demonstrating the advantages of the preparation method to obtain Ni-Co alloys. Although the results of adsorption of ethanol followed by diffuse reflectance infrared fourier transformed spectroscopy (DRIFTS) showed acetate species strongly adsorbed on the catalyst’s surface, the material (Ni0.7Co0.3/La0.8Ce0.2) with the lowest particle size was the most stable system leading to the lowest amount of carbon deposits during ethanol decomposition. This catalyst showed the better performance, with a higher ethanol conversion (98.4%) and hydrogen selectivity (75%). All catalysts exhibited carbonaceous deposits, which were an ordered and disordered carbon phase mixture.

Preparation and phosphate adsorptive properties of metal oxide-loaded granular activated carbon and pumice stone

Technology of phosphate adsorption is important in the field of wastewater treatment to prevent eutrophication. Granulation of powdered adsorbent maintaining the adsorption performance is essential for designing a column adsorption process. Herein, granular activated carbon (GAC) and pumice stone (PMC) containing lanthanum cerium or iron oxide were prepared and their phosphate adsorptive properties were then compared by a batch method in a diluted solution (1.9 mg-P/dm3). Phosphate adsorption was relatively slow compared with the adsorption on powdered adsorbent, and adsorption process continued for more than 380 h. Lanthanum oxide-loaded GAC and PMC showed large phosphate uptakes of 5–8 mg-P/g-ad, corresponding to the phosphate uptakes above 60 mg-P per gram of La(OH)3 in the granules. Cerium oxide-loaded GAC and PMC showed relatively large phosphate uptakes of 3–6 mg-P/g, whereas iron oxide-loaded ones showed considerably smaller phosphate uptakes of 0.5–2.5 mg-P/g. The intraparticle surface diffusivity of the phosphate ions was derived for the lanthanum oxide-loaded granules from the concentration decay curve, using the diffusion equation with the Langmuir-type adsorption isotherm. The diffusivities were approximately 1 × 10−11 m2/h independent of the types of support or particle size, indicating that the phosphate adsorption rates were strongly influenced by the external surface area of the granule. Structural characterization of the metal oxide-loaded GAC before and after the phosphate adsorption suggests that the phosphate adsorption on the lanthanum oxide-loaded GAC progresses by the chemical reaction from La(OH)3 to phosphate-displaced La2(CO3)38H2O, whereas that on the cerium oxide-loaded GAC progresses by the ion exchange with surface hydroxyl group of the CeO2 particle. The above results suggest that the lanthanum oxide- and cerium oxide-loaded GAC and PMC are promising materials for column phosphate removal in municipal wastewater.

Sustainable cool pigments based on iron and tungsten co-doped lanthanum cerium oxide with high NIR reflectance for energy saving

The novel non-toxic yellow-orange inorganic pigments La2Ce2-xW0.5xFe0.5xO7+δ (x = 0.1, 0.3, 0.5, 0.7, 0.9) with high near-infrared reflectance have been synthesized. The crystal structure, chemical composition, optical properties (reflectance and absorption properties) and color performance of the synthesized pigments were characterized by several techniques. X-ray diffraction analysis indicated the disordered defect fluorite-type structure of the pigments. The typical pigment La2Ce1.5W0.25Fe0.25O7+δ possessed the high NIR solar reflectance of 82.05% with orange color (L* = 77.21, a* = 8.79, b* = 35.80). Also the influence of calcination temperature has been studied, the higher temperature resulted in enhanced color and slightly reduced reflectance properties. The applicability of typical pigment La2Ce1.7W0.15Fe0.15O7+δ (calcined at 1150 °C) was tested on a galvanized sheet, the coating improved the NIR solar reflectance from 19.18% to 71.07%. The acid/alkali resistance studies confirmed the pigments were chemically stable. Thus, the synthesized pigments with vivid yellow-orange color and high NIR reflectance have exhibited application potentials.

Hot corrosion studies on plasma sprayed bi-layered YSZ/La 2 Ce 2 O 7 thermal barrier coating fabricated from synthesized powders

Abstract La 2 Ce 2 O 7 (LCO) with a pyrochlore structure has been considered as a propitious thermal barrier coating (TBC) system possessing high temperature (>1200 °C) phase stability. In the present study, double ceramic layer of yttria stabilized zirconia (YSZ) and lanthanum cerium oxide (La 2 Ce 2 O 7 , LCO) TBCs are fabricated by atmospheric plasma spraying (APS). Individual LCO and 8YSZ and bilayered LCO/YSZ coatings are developed using flowable YSZ and LCO powders synthesized by co-precipitation and combustion routes respectively and are characterized for phase and microstructure. The coatings subjected to hot corrosion (Na 2 SO 4 +V 2 O 5 salt at 910 °C for 30 h) are characterized by X-ray Diffractometry and Scanning Electron Microscopy and Energy Dispersive X-Ray Spectroscopy. XRD shows the phase transformation of YSZ from tetragonal to monoclinic zirconia accompanied by the formation of LaVO 4 and YVO 4 as hot corrosion products. Considerable decrease in volume fraction of monoclinic zirconia phase has been observed for bilayered LCO/YSZ coating compared to 8YSZ single layer.

Investigation of ionic conductivity of lanthanum cerium oxide nano crystalline powder synthesized by co precipitation method

Lanthanum (La) doped Ceria (CeO2) electrolyte has attracted considerable interest, as a candidate material for solid oxide fuel cells (SOFCs). The ionic conductivity of La doped CeO2 system (La2Ce2O7) nano-particles synthesized by the co-precipitation method has been investigated. The cubic fluorite structure was observed from the structural analysis of the material. Morphology of the sintered pellets are observed by scanning electron microscope (SEM), respectively. From the results of impedance spectroscopy from temperature range of room temperature to 400°C, the oxide ion conductivity due to proton charge carrier was observed. Thermogravimetric analysis (TGA) was performed on the material to check stability of phase at high temperature.

Preparation and Infrared Radiation Property of Lanthanum-cerium Oxide Ceramics by (Ca,Fe) Co-doping

以La 2 O 3 、CeO 2 、CaO和Fe 2 O 3 为起始原料, 采用高温固相烧结工艺制备得到(Ca,Fe)共掺铈酸镧(La 1.9 Ca 0.1 Ce 1.9 Fe 0.1 O 7 )红外辐射陶瓷材料。采用X射线衍射仪、扫描电子显微镜、能谱仪、紫外–可见–近红外(UV-Vis-NIR)分光光度计分别对样品的物相组成、显微结构、化学成份、UV-Vis-NIR反射率及UV-Vis吸收进行了表征, 同时采用IR-2双波段红外发射率测量仪测试了样品3~5 μm波段的红外发射率。结果表明: 掺杂元素(Ca, Fe)均固溶进入铈酸镧晶格, 共掺后样品的晶体结构也为萤石结构; (Ca,Fe)共掺样品内部形成杂质能级, 强化了自由载流子吸收与杂质能级吸收, 使样品红外短波段(0.75~5 μm)性能由高反射转变为高吸收(辐射), 其中在0.75~2.5 μm波段的平均红外吸收率为0.88, 3~5 μm波段的红外发射率为0.752, 与未掺杂样品相比分别提高了1660%与60%。

Retraction of “Synergistic Effect of Expandable Graphite and Lanthanum Cerium Oxide on Intumescent Fire Retardant Coating for Structural Applications”

Intumescent fire retardant coatings (IFRC), as a passive form of fire protection, are extensively used by the oil and gas industries to protect steel against corrosion and fire. In this study, an epoxy based IFRC was prepared with different flame retardants. IFRC was reinforced with lanthanum cerium oxide (LCO) to study its effect on thermal insulation before and after immersion in salt water for a period of one month. Characterization techniques include FESEM with EDS, TGA, XPS, XRD,and Pyrolysis GC-MS. Results demonstrated that coating with 4 wt % LCO and 3 wt % EG provided better thermal insulation both before and after salt water immersion and exhibited less weight loss as per TGA analysis.