CeO2 Nanopowder Research Articles

Tuning Chemical and Morphological Properties of Ceria Nanopowders by Mechanochemistry.

Cerium oxide powders are widely used and are of fundamental importance in catalytic pollution control and energy production due to the unique chemical properties of CeO2. Processing steps involved in catalyst preparation, such as high-temperature calcination or mechanical milling processes, can alter the morphological and chemical properties of ceria, heavily affecting its final properties. Here, we focus on the tuning of CeO2 nanopowder properties by mild- and high-energy milling processes, as the mechanochemical synthesis is gaining increasing attention as a green synthesis method for catalyst production. The textural and redox properties were analyzed by an array of techniques to follow the aggregation and comminution mechanisms induced by mechanical stresses, which are more prominent under high-energy conditions but strongly depend on the starting properties of the ceria powders. Simultaneously, the evolution of surface defects and chemical properties was followed by Raman spectroscopy and H2 reduction tests, ultimately revealing a trade-off effect between structural and redox properties induced by the mechanochemical action. The mild-energy process appears to induce the largest enhancement in surface properties while maintaining bulk properties of the starting materials, hence confirming its effectiveness for its exploitation in catalysis.

Tribological, oxidation and corrosion properties of ceramic coating on AISI H13 steel by rare earth-Cr composite boronizing

In this paper, a rare earth-Cr composite boronizing method to prepare boride ceramic coatings for AISI H13 steel was proposed. The effect of rare earth elements and Cr on the microstructure, hardness, wear resistance, high temperature oxidation resistance, and corrosion of boride ceramic layers was researched. The characteristics of the boride layers were investigated by means of X-ray diffraction (XRD), scanning electron microscope (SEM), electron probe microanalysis (EPMA), wear tests, high-temperature oxidation tests, and corrosion immersion tests, etc. The results showed that the boride layer comprised of Fe2B, FeB, CrB and Cr2B phases. The addition of rare earth CeO2 and Cr nanopowder promoted the growth of the boride layer, and its surface hardness increased by 3.5 times compared with that of tempered AISI H13 steel. In addition, the addition of CeO2 and Cr significantly reduced the wear rate of the boride layer, with the surface wear mechanism being abrasive oxidative wear. Furthermore, the oxidation rate of the boride layer was 71 % lower than that of AISI H13 steel, demonstrating excellent high-temperature oxidation resistance; and the boride layer showed good acid corrosion resistance in corrosion immersion tests.

Study of Structural and Electrical Properties of CeO2 Added Li1.3Al0.3Ti1.7(PO4)3 Ceramic for Lithium-Ion Battery Application

LATP ceramic electrolytes have been prepared by sintering combinations of LATP powder and CeO2 nano-powder. The phase formation of LiTi2(PO4)3 (LTP) and the secondary phase formation of the fine CePO4 particles scattered in LATP ceramics were confirmed by powder X-ray diffraction. The morphology of ceramic sample was studied using scanning electron microscopy. The elemental distribution was investigated using energy-dispersive X-ray spectroscopy. The CeO2 addition improves the electrical conductivity. CeO2 nano-powder added LATP ceramics with 3 wt% CeO2 sintered at 800 °C for 1 h have a high ionic conductivity of 0.56 mS.cm−1 at room temperature with an activation energy of 0.15 eV.

Precipitation Synthesis of CeO2 Nanopowder Pigment

Nanopowder pigments of CeO2 and CeO2:Fe were synthesized by precipitation method at a moderate calcination temperature of 500oC. The pigments exhibited pale yellow for CeO2 nanopowder and brick red for CeO2:Fe nanopowder. Both pigments possessed mesoporous and cubic fluorite structures of CeO2. The incorporation of Fe into CeO2 reduced crystallite size and increased surface area. Moreover, it widens bandgap energy and significantly improved the absorption property of CeO2 nanopowder.

Electron diffraction characterization of nanocrystalline materials using a Rietveld-based approach. Part I. Methodology.

Transmission electron microscopy is a powerful experimental tool, very effective for the complete characterization of nanocrystalline materials by employing a combination of imaging, spectroscopy and diffraction techniques. Electron powder diffraction (EPD) pattern fingerprinting in association with chemical information from spectroscopy can be used to deduce the identity of the crystalline phases. Furthermore, EPD has similar potential to X-ray powder diffraction (XRPD) for extracting additional information regarding material specimens, such as microstructural features and defect structures. The aim of this paper is to extend a full-pattern fitting procedure, broadly used for analysing XRPD patterns, to EPD. The interest of this approach is twofold: in the first place, the relatively short times involved with data acquisition allow one to speed up the characterization procedures. This is a particularly interesting aspect in the case of metastable structures or kinetics studies. Moreover, the reduced sampling volumes involved with electron diffraction analyses can better reveal surface alteration layers in the analysed specimen which might be completely overlooked by conventional bulk techniques. The first step forward to have an effective application of the proposed methodology concerns establishing a reliable calibration protocol to take into correct account the instrumental effects and thus separate them from those determined by the structure, microstructure and texture of the analysed samples. In this paper, the methodology for determining the instrumental broadening of the diffraction lines is demonstrated through a full quantitative analysis based on the Rietveld refinement of the EPD. In this regard, a CeO2 nanopowder reference specimen has been used. The results provide indications also on the specific features that a good calibration standard should have.

Синтез нанокомпозита графен-СеО2 с использованием додециламина

A method is proposed for the synthesis of nanostructured composites based on graphene and CeO2, which combines sol-gel and sonochemical methods. A feature of the method is that when the graphene content is not more than 2 wt. %, its uniform distribution in the volume of the material is achieved without the formation of an impurity phase. In addition, oxygen-free graphene with a sheet thickness of 3 – 5 nm was used in the synthesis as a suspension obtained by ultrasonic exfoliation in an alkalized by KOH aqua-alcohol solution of dodecylamine. The formation of a composite in a mixed colloid occurs in such a way that the sol-gel transition and subsequent crystallization of nano-CeO2 occur on the graphene sheets. However, the chemical interaction of the latter and CeO2 in the composite is not observed, which contributes to the preservation of the sp2-electrons system of graphene and, as a result, the preservation of its unique electronic properties. The graphene sheets form a layered structure of composite agglomerates, and isolated CeO2 nanocrystals are incorporated into these differently oriented layers. It has been determine that CeO2 dispersion in the composite is higher than in pure CeO2 nanopowder. Estimating the phase and chemical purity of the synthesized composite, it can be argued that the developed method for obtaining nanostructured powders based on graphene and CeO2 is promising as the basis for an economical and environmentally friendly technology for the production of initial substances for fine-grained electrical ceramics.

CuFeO2–CeO2 nanopowder catalyst prepared by self-combustion glycine nitrate process and applied for hydrogen production from methanol steam reforming

Hydrogen (H2) is being considered as an alternate renewable energy carrier due to the energy crisis, climate change and global warming. In the chemical industry, hydrogen production is mainly accomplished by the steam reforming of natural gas. In the present study, CuFeO2–CeO2 nanopowder catalyst with a heterogeneous delafossite structure was prepared by the self-combustion glycine nitrate process and used for steam reforming of methanol (SRM). The precursor solution was fabricated from Cu–Fe–Ce metal-nitrate mixed with glycine and an aqueous solution. The prepared CuFeO2–CeO2 nanopowder catalyst was studied by different physical and chemical characterization techniques. The prepared CuFeO2–CeO2 nanopowder catalyst was immensely porous with a coral-like structure. The BET surface area measurement revealed that the specific surface area of as-combusted CuFeO2–CeO2 nanopowder varied from 5.6248 m2/g to 19.5441 m2/g. In addition, the production rate of CuFeO2–CeO2 was improved by adding CeO2 and adjusting the feeding rate of the methanol. The highest H2 generation rate of the CuFeO2–CeO2 catalyst was 2582.25 (mL STP min−1 g-cat−1) at a flow rate of 30 sccm at 400 °C. Hence, the high specific surface area of the 70CuFeO2–30CeO2 nanopowder catalyst and the steam reforming process could have a very important industrial and economic impact.

Electronic structure of surface complexes between CeO2 and benzene derivatives: A comparative experimental and DFT study

Surface modification of CeO2 nano-powder, synthesized by a self-propagating room temperature method with salicylate-type ligands (salicylic acid and 5-aminosalicylic acid) as well as catecholate-type ligands (catechol, 3,4-dihydroxybenzoic acid, caffeic acid and 2,3-dihydroxy naphthalene), induces the appearance of absorption in the visible spectral region due to the interfacial charge transfer (ICT) complex formation. Thorough characterization involving transmission electron microscopy, XRD analysis, and nitrogen adsorption-desorption isotherms, revealed that loosely agglomerated CeO2 particles of the size ranging from 2 to 4 nm have cubic fluorite structure and specific surface area of 140 m2/g. The attachment of salicylate- and catecholate-type of ligands to the surface of CeO2 powders leads to the formation of colored powders with tunable absorption in the visible spectral region. The density functional theory calculations with properly design model systems were performed to estimate the alignment of energy levels of various inorganic/organic hybrids. A reasonably good agreement between calculated values and experimental data was found.

Improving the sinterability of CeO2 by using plane-selective nanocubes

CeO2 nanocubes with (100) surface orientation are successfully synthesized and found to facilitate the sinterability of CeO2 material. The CeO2 nanocubes show a much-improved sinterability relative to CeO2 nanoparticles prepared by the conventional citric-nitrate method. The nanocubes can be successfully sintered at a relatively low temperature of 1200 °C without using any sintering aids. In contrast, a pellet using conventional CeO2 nano-powder obtained from the conventional citric-nitrate method can be densified only after sintering at 1400 °C, which is 200 °C higher than that for the CeO2 nanocube sintering, although the starting particle size of both CeO2 samples is similar. Density functional theory indicates that the surface energy of the (100) plane is significantly higher than that of the (111) plane, which is the more typical surface presentation of conventional CeO2 particles. This high surface energy allows fast growth of the CeO2 nanocubes during sintering, contributing to their improved sinterability.

Fabrication and Characterization of Cu Doped CeO<sub>2</sub> by Hydrothermal Process for Antimicrobial Activity

Cu doped CeO2 nanopowder was synthesized by hydrothermal process at 180°C for 2~10h. The average size and distribution of the synthesized Cu doped CeO2 nanopowder was controlled by reaction times. The crystallinity of the synthesized Cu doped CeO2 nanoparticles was investigated by X-ray diffraction (XRD). The morphology of the synthesized Cu doped CeO2 nanoparticles was observed by FE-SEM. The specific surface area of the synthesized Cu doped CeO2 nanoparticles was measured by BET. The crystal size of the synthesized Cu doped CeO2 nanoparticles decreased with decreasing reaction times. The average size of the synthesized Cu doped CeO2 nanoparticles was below 10nm and narrow, respectively. The shape of the synthesized Cu doped CeO2 nanoparticles was spherical type. The specific surface area of the synthesized Cu doped CeO2 nanoparticles increased with decreasing reaction times. Antibacterial properties of Cu doped CeO2 were analyzed by MIC method. The synthesized Cu doped CeO2 nanopowders showed antibacterial properties against E.coli and B.sub bacteria.

Selective oxidation of cyclohexane: Ce promotion of nanostructured manganese tungstate

Cyclohexane selective oxidation over nanostructured MnWO4 promoted with increasing amounts of Ce (1–5 wt%) has been investigated at mild conditions using molecular oxygen as oxidant. MnWO4 nanorods were found to be an active catalyst for cyclohexane selective oxidation with selectivity to KA oil (cyclohexanol + cyclohexanone) of approximately 85%. The catalytic performance was improved by impregnation with 1 wt% Ce while the textural properties and crystallinity were preserved and Ce was well-dispersed on the surface. XPS analysis of 1%Ce-MnWO4 showed Ce to be present mainly as Ce3+, which is known to promote oxygen adsorption, activation, and mobility. At higher Ce content, the proportion of Ce4+ increased to be the main Ce species and large, heterogeneously-dispersed Ce oxide particles are formed on the catalyst surface. The lower Ce3+ content reduces the promoting effect while the large Ce oxide particles block access to the active sites on the surface of the MnWO4 nanorod. MnWO4 and 1%Ce-MnWO4 nanorods were shown to retain their selective oxidation performance in consecutive reaction runs. Surprisingly, physical mixtures of nanostructured MnWO4 and a CeO2 nanopowder showed enhanced selective oxidation activity compared to MnWO4 alone reaching a plateau at 25–50 wt% CeO2, whereas CeO2 nanopowder itself was found to be inactive at the reaction conditions. Ce promoted MnWO4 shows promise as a catalyst for selective oxidation of cyclohexane and performs at least as well as the most active non-metallic heterogeneous catalysts reported in the literature.

Solution Combustion Synthesis of High Surface Area CeO2 Nanopowders for Catalytic Applications: Reaction Mechanism and Properties

High surface area cerium oxide (CeO2) is an important material as a catalyst component in many applications owing to its unique redox properties, high oxygen storage capacity, and ability to disperse metal on its surface. In this work, CeO2 nanopowders were prepared by solution combustion synthesis (SCS), varying the synthesis parameters in terms of precursor oxidizer (cerium nitrate hexahydrate and cerium ammonium nitrate), fuel (glycine and hydrous hydrazine), fuel-to-oxidizer ratio (0.5–3), and gas generating agent (ammonium nitrate). These parameters strongly influence the combustion features, including combustion temperature and amount of gas evolved during combustion, and, in turn, the properties of formed CeO2 powders. On the basis of the experimental results, the combustion reaction mechanism and correlation between the SCS parameters and properties of the resulting powder are discussed. The samples were characterized using X-ray diffraction, transmission electron microscopy, Raman, X-ray photoelectron spectroscopy, and Brunauer–Emmett–Teller techniques. The tailored CeO2 nanopowder synthesized using hydrous hydrazine fuel, fuel-to-oxidizer ratio 2, and ammonium nitrate/metal nitrate ratio 4 exhibited small CeO2 crystallite size (7.9 nm) and high surface area (88 m2/g), which is the highest value among all prior reported SCS-derived CeO2 powders.

Hydrogen sorption improvement of MgH2 catalyzed by CeO2 nanopowder

In this study, we investigate the effects of the addition of CeO2 nanopowder on the hydrogen storage properties of MgH2. The 5-wt% CeO2-added MgH2 sample showed improvement in the hydrogenation rate compared with pristine MgH2, with the CeO2-added MgH2 sample releasing about 3.6-wt% hydrogen within 30 min at 320 °C whereas the as-received MgH2 released less than 1.0-wt% hydrogen under the same conditions. Additionally, with respect to absorption kinetics, the total hydrogen absorption capacity of the MgH2 + 5-wt% CeO2 composite increased from 3.5 wt% to 3.8 wt% in 10 min at 320 °C. From a Kissinger plot of the differential scanning calorimetry at different heating rates, the apparent activation energy was determined to be 133.62 kJ/mol for the as-milled MgH2 and 108.65 kJ/mol for the 5-wt% CeO2-added MgH2. This indicates that adding CeO2 nanopowder decreases the activation energy for the hydrogen desorption of MgH2. The formation of new phases of CeH2 by the doping of CeO2 nanopowder with MgH2 after the dehydrogenation and rehydrogenation processes was observed in the X-ray diffraction spectra. It is believed that the enhancement of the hydrogenation performance of the MgH2/CeO2 composite is due to combination of the CeH2 active species and CeO2 itself.

Collective magnetic response of CeO2 nanoparticles

The magnetism of nanoparticles and thin films of wide-bandgap oxides that include no magnetic cations is an unsolved puzzle. Progress has been hampered both by the irreproducibility of much of the experimental data, and the lack of any generally-accepted theoretical explanation. The characteristic signature is a virtually anhysteretic, temperature-independent magnetization curve which saturates in an applied field that is several orders of magnitude greater than the magnetization. It appears as if a tiny volume fraction, < 0.1%, of the samples is magnetic and that the energy scale of the problem is unusually high for spin magnetism. Here we investigate the effect of dispersing 4 nm CeO2 nanoparticles with powders of gamma-Al2O3, sugar or latex microspheres. The saturation magnetization, Ms ~ 60 A/m for compact samples, is maximized by 1 wt% lanthanum doping. Dispersing the CeO2 nanopowder reduces its magnetic moment by up to an order of magnitude. There is a characteristic length scale of order 100 nm for the magnetism to appear in CeO2 nanoparticle clusters. The phenomenon is explained in terms of a giant orbital paramagnetism that appears in coherent mesoscopic domains due to resonant interaction with zero-point fluctuations of the vacuum electromagnetic field. The theory explains the observed temperature-independent magnetization curve and its doping and dispersion dependence, based on a length scale of 300 nm that corresponds to the wavelength of a maximum in the UV absorption spectrum of the magnetic CeO2 nanoparticles. The coherent domains occupy roughly ten percent of the sample volume.

Effect of Sintering Temperature on the Mechanical Properties of Nanostructured Ceria-Zirconia Prepared by Colloidal Process

The demand for tetragonal zirconia as a dental restorative material has been increasing because of its excellent mechanical properties and resemblance to natural tooth color, as well as its excellent biological compatibility. Cerium oxide (CeO2) has been added to yttria-stabilized zirconia (Y-TZP), and studies have demonstrated that the stability of the tetragonal phase can be significantly improved. Y-TZP with 5wt% CeO2 as a second stabilizer was developed via colloidal process, followed by a suitable sintering process. According to the literature, the sintering process is the most crucial stage in ceramic processing to obtain the most homogeneous structure with high density and hardness. This study aims to investigate the effect of sintering temperature on the mechanical properties of nanostructured ceria–zirconia fabricated via colloidal processing and slip casting process with cold isostatic pressing (CIP). Twenty-five pellet specimens were prepared from ceria–zirconia with 20 nm particle size. CeO2 nanopowder was mixed with Y-TZP nanopowder via colloidal processing. The consolidation of the powder was done via slip casting followed by CIP. The samples were divided into five different sintering temperatures with. Results from FESEM, density and hardness analyses demonstrated statistically significant increase in density and hardness as the sintering temperature increased. The hardness increased from 4.65 GPa to 14.14 GPa, and the density increased from 4.70 to 5.97 (g/cm3) as the sintering temperature increased without changing the holding time. Sintering Ce-Y-TZP at 1600 °C produced samples with homogenous structures, high hardness (14.14 GPa), and full densification with 98% of the theoretical density.

UV-Light Absorption and Photocatalytic Properties of Zn-Doped CeO&lt;sub&gt;2&lt;/sub&gt; Nanopowders Prepared by Ultrasound Irradiation

Ceria (CeO2) nanopowders doped with various Zinc (Zn) compositions were synthesized from solution by irradiating ultrasound waves. Ultrasound waves were irradiated to aqueous/isopropanol solution of cerium nitrate and zinc nitrate mixtures. Aqueous solution of ammonium hydroxide was droped into that solution until pH becomes 10. Dried precipitates were calcinated at 100°C to form CeO2 nanopowders. X-ray Diffraction (XRD) analysis shows the CeO2 nanopowder possess fluorite cubic structure. Ultrasound irradiation resulted in nanometric powder of CeO2 with spherical in shape. The addition of Zn into CeO2 reduces the particle size and shows strong absorbance in the ultra–violet (UV) region. Moreover, the addition of 20 mol% Zn is inhibiting photocatalytic activity of CeO2 under sunlight irradiation. These results suggest that Zn-doped CeO2 is more promising for UV radiation protection with no presence photocatalytic activity.

Abatement of toluene from polluted air over Mn/Clinoptilolite–CeO2 nanopowder: Impregnation vs. ultrasound assisted synthesis with various Mn-loading

Total oxidation of toluene over Mn(5%, 10%, 15%)/Clinoptilolite–CeO2 nanocatalysts was performed. Mn was doped via two different methods of impregnation and sonochemistry. The catalysts were characterized by XRD, FESEM, EDX, BET and FTIR analyses. The physicochemical characterizations showed superior properties of sonochemically synthesised nanocatalysts like homogenous morphology, small and dispersed particles, and strong interaction. Addition of CeO2 as a promoter to acid-treated clinoptilolite remarkably increased catalytic activity. XRD analysis demonstrated acid treatment of clinoptilolite induces noticeable decrease in crystals size and their crystallinity, while the specific surface area increased. Furthermore, no obvious peaks related to MnOx were found in XRD patterns even at high loadings of Mn which might be attributed to the high dispersion of particles in sonochemistry method. Due to the effect of sonication power, even at high loadings of Mn(15%), the morphology of the catalyst was agglomeration free and surface area was high. Comparison of catalytic activity of sonochemically and impregnated Mn(5%)/Clinoptilolite–CeO2 nanocatalyst showed that sonochemically synthesized catalyst can oxidize toluene 5–10% more than impregnated one at all temperature ranges. Increasing metal content enhanced the catalytic activity.

Preparation of CeO2 Nano Rods Through a Sonication‐Assisted Precipitation

A CeO2 nanopowder has been synthesized using sonication‐assisted precipitation. The use of ultrasonics during precipitation showed potential morphology control during synthesis. The sonication‐assisted precipitation with highly aqueous base (20 M NaOH) successfully induced the formation of a one‐dimensional nanostructure of CeO2 rods with a homogeneous shape and size (TEM: 24 nm diameter and 129 nm long). A conventional precipitation under the same conditions provided the CeO2 in nonuniform sizes and shapes. Heat treatment (1100°C for 4 h) was required for CeO2 formation when (NH4)2C2O4 was used instead of NaOH. The concentration of the precipitation agent (15–20 M) strongly affected the size and shape of the product. Importantly, according to the temperature‐programmed reduction/oxidation study, the CeO2 prepared using the sonication‐assisted route showed a relatively higher level of reversible oxygen storage capacity (2384 μmol/g), compared with the CeO2 prepared by conventional route (1748 μmol/g).

Dispersibility of CeO2 Nanoparticles in Water–Ethanol Suspensions

In order to improve the dispersibility of CeO2 nanoparticles and reduce the environmental pressure, the dispersibility and stability of CeO2 nano-powder in water-ethanol suspensions was investigated in this paper. The results show that with the increasing of volume fraction of ethanol, the sedimentation rate of CeO2 nanoparticles firstly decreases and then increases. When the volume fraction of ethanol is between 30% and 50%, the dispersibility of CeO2 nanoparticles is better. Only mixing water and ethanol at a certain proportion as the dispersion medium can nano-sized CeO2 polishing slurry have the advantages of both and better dispersing effect.

Synthesis and characterization of nanostructured CeO2 with dyes adsorption property

The nanostructured cerium dioxide (CeO2) has been successfully fabricated using a simple precipitation method. Its characteristics were evaluated using TG-DTA, DR-UV-Vis, XRD, FTIR and TEM. The results showed that the nanostructured CeO2 has high purity and good crystalline nature, with face centered cubic (fcc) phase and the average diameter of CeO2 single crystal about 14 nm. Performance evaluation of the synthesized CeO2 samples showed that the nanostructured CeO2 has a strong adsorption toward acid orange-10 (AO-10) and congo red (CR) in aqueous solution. Under given experimental conditions (dye concentration of 15 mg/l, adsorbent dosage of 1 g/l, reaction temperature of 30 ? 1?C), it was estimated that the adsorption equilibrium for AO-10 and CR occurred at 60 min and 90 min of reaction time, respectively, with total removal of 96.82% for AO-10 dye and 93.55% for CR dye. The results suggested that the CeO2 nanopowder could be potentially used as an efficient adsorbent for the removal of synthetic organic dyes in aqueous solution and may address for future concern in the area.