Formation Of CeO2 Research Articles

Synthesis, characterization and thermal analysis of solid-state lanthanide mandelates in CO2 and N2 atmospheres.

Solid-state Ln-L compounds, where Ln stands for trivalent lanthanides and L is mandelate (C 6 H 5 CH(OH)CO 2 -) have been synthesized. Elemental analysis, complexometry, infrared spectroscopy (FTIR), simultaneous thermogravimetry and differential thermal analysis (TG-DTA), simultaneous thermogravimetry and differential scanning calorimetry (TG-DSC) coupled to FTIR have been used to characterize and to study the thermal stability and thermal decomposition of these compounds in CO 2 and N 2 atmospheres. In both atmospheres, the dehydration of the lanthanum, cerium and samarium to lutetium compounds occurs in a single step, while for praseodymium and neodymium ones the dehydration occurs in two consecutive steps. The thermal decomposition of the anhydrous compounds occurs in several consecutive and / or overlapping steps with the formation of CeO 2 , Pr 6 O 11 , Tb 4 O 7 and Ln 2 O 3 (Ln = La, Nd, Sm to Gd and Dy to Lu) in dynamic CO 2 atmosphere or CeO 2 and Ln 2 O 3 (Ln = La, Pr to Lu) in dynamic N 2 one, as final residue.

Effect of potassium substituted for A-site of SrCe0.95Y0.05O3 on microstructure, conductivity and chemical stability

The chemical stability of potassium substituted for A-site of SrCe0.95Y0.05O3 specimens was examined under CO2 atmosphere treated at 600°C and further analyzed by X-ray diffractometer to see their CO2-resisted capabilities. According to thermodynamic data, the Gibbs free energy of CeO2 was lower than that of SrCO3 at the temperature of 600°C. Thus the formation of CeO2 might be faster than that of SrCO3 in SrCeO3− based materials under CO2 atmosphere. Unfortunately, the chemical stability of SrCe0.95Y0.05O3 materials in CO2 atmosphere was reduced with increasing potassium-substituted amount. The microstructures of Sr1−xKxCe0.95Y0.05O3 sintered specimens were identified using field emission scanning electron microscope. The conductivity in moisture H2 atmosphere (RH 30%) was increased with increasing potassium-substituted concentration. The conductivity reached a maximum of 0.0081 Scm-1 at 900°C for Sr0.95K0.05Ce0.95Y0.05O3 sintered specimens in moisture H2 atmosphere (RH 30%). Potassium substituted for A-site of SrCe0.95Y0.05O3 could improve the conductivity but not CO2-resisted capability.

Electrochemical performance and carbon deposition resistance of Ce-doped La0.7Sr0.3Fe0.5Cr0.5O3-δ anode materials for solid oxide fuel cells fed with syngas

Ce-doped La0.7Sr0.3Fe0.5Cr0.5O3-δ (Ce-LSFC) perovskite anode catalysts for solid oxide fuel cells are successfully synthesized by a modified combustion method for the first time. The pure perovskite structure without formation of CeO2 is obtained when the content of Ce ≤ 10%. Compared with La0.7Sr0.3Fe0.5Cr0.5O3-δ anode, Ce-LSFC anode not only shows much higher catalytic activity towards the oxidation of syngas with less carbon deposition, but also displays better regeneration from coking. The enhanced performance is attributed to the more available oxygen vacancies in lattice and better oxygen mobility after doping with Ce.

Ex-situ studies on calcinations of structural, optical and morphological properties of post-growth nanoparticles CeO2 by HRTEM and SAED

Nanocrystalline particles of Cerium Oxide (CeO2) have been prepared by the chemical precipitation method using Cerium nitrate and Urea with a molar ratio of 1:2. The results revealed that the formation of CeO2 fine particles is influenced by molar ratio of metal nitrates to fuel. Well faceted CeO2 nanoparticles, were synthesized by thermal-assisted dissociation method at reflux temperature in a short period of time. A possible mechanism for synthesis of such highly pure and stable nanoparticles is tentatively proposed by thermogravimetry-differential thermal analysis (TG –DTA) study. The powders were investigated by X-ray diffraction (XRD), Transmission electron microscopy (TEM), selected area electron diffraction (SAED), high resolution transmission electron microscopy (HRTEM). In addition, uniform particles, size distribution and purity of samples are highly dependent on the applied chemical precipitation method. Raman spectroscopy and Electron Diffraction Analysis confirmed the fluorite structure of bulk CeO2.

Influence of sintering temperature on secondary phases formation and microwave dielectric properties of Ca2Ce2Ti5O16 ceramics

Abstract Ca2Ce2Ti5O16 dielectric ceramics prepared by conventional solid-state ceramic route was investigated. Phase composition and microwave dielectric properties were measured using XRD and Vector network analyzer, respectively. XRD analysis of the calcined and sintered samples revealed the formation of CeO2 and another unidentified phase (that vanished at ≥ 1400 °C) as secondary phases along with the parent Ca2Ce2Ti5O16 phase. The amount of the parent Ca2Ce2Ti5O16 phase increased with increasing sintering temperature from 1350 °C to 1450 °C accompanied by a decrease in the apparent density. The density decreased but ɛr and Qu f o increased with sintering temperature. An er ~ 81.5, Qu fo ~5915 GHz and t f ~ 219 GHz were achieved for the sample sintered at 1450 °C.

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).

Development of electrochemical biosensor with ceria–PANI core–shell nano-interface for the detection of histamine

A mediator-free electrochemical biosensor with CeO2–PANI nano-interface for sensing histamine using diamine oxidase (DAO) has been developed. CeO2–PANI core–shell nanoparticles were prepared by hydrothermal method. The field emission scanning electron microscopy (FE-SEM) revealed the aggregated spherical morphology of CeO2. The core–shell formation of CeO2–PANI was confirmed with field emission transmission microscopy (FE-TEM). The polycrystallinity of CeO2 and CeO2–PANI was confirmed using X-ray diffraction (XRD). Immobilization of DAO with CeO2–PANI was confirmed with Fourier transform infrared spectroscopy (FT-IR). Electrochemical studies were carried out through cyclic voltammetry and amperometry using modified GCE/CeO2–PANI/DAO as a working electrode, Ag/AgCl saturated with 0.1M KCl as a reference electrode and platinum (Pt) wire as a counter electrode. The linear range was observed from 0.45 to 1.05mM with a sensitivity of 724.94μAcm−2mM−1. Michaelis–Menten constant was calculated as 0.798mM. It exhibited limit of detection of 48.7μM, limit of quantification of 132.4μM with a response time of <1s and good shelf life of 86% till 18 days. Also the developed biosensor was applied on tiger prawn to estimate the histamine content.

CO oxidation over Au and Pd nanoparticles supported on ceria–hafnia mixed oxides

In this work, Au and Pd nanoparticles supported on pure CeO2 and CeO2–HfO2 mixed oxides have been prepared using microwave irradiation. The structural, surface and bulk properties have been investigated using XRD, BET, UV–Vis, Raman spectra, TPR and TEM images. XRD and Raman spectra results confirm the formation of CeO2–HfO2 solid solutions with high degree of dispersion of Au and Pd nanoparticles. TEM images show that Au and Pd particles are nanosized with almost uniform shape. A TPR study shows that the presence of Au effectively enhances the reduction of pure supports to lower temperatures. The catalytic activity results show enhancement of the catalytic activities of the supports after loading with Au and Pd nanoparticles. Moreover, the samples that contain Au nanoparticles exhibit higher catalytic activities, which increases with the extent of Au loading.

Imaging the continuous hydrothermal flow synthesis of nanoparticulate CeO2 at different supercritical water temperatures using in situ angle-dispersive diffraction

In situ high-energy synchrotron X-ray diffraction, a non-destructive synchrotron-based technique was employed to probe inside the steel tubing of a continuous hydrothermal flow synthesis (CHFS) mixer to spatially map, for the first time, the superheated water crystallisation of nanocrystalline ceria (CeO2) at three different (superheated-water) temperatures representing three unique chemical environments within the reactor. Rapid hydrothermal co-precipitation at the three selected temperatures led to similarly sized ceria nanoparticles ranging from 3 to 7nm. 2D maps of CeO2 formation were constructed from the intensity and corresponding full width at half maximum (FWHM) values of the two most intense ceria reflections (111) and (002) for all three water inlet temperatures (350, 400 and 450°C at 24MPa) and subsequent changes in the particle size distribution were analysed. The accompanying high-resolution transmission electron microscopy (HRTEM) and tomographic particle size maps have confirmed that the mean ceria particle size slightly increases with temperature. This X-ray tomographic imaging study amounted to a formidable technical and engineering challenge, nevertheless one that has been met; this represents a significant achievement in imaging science, given the dynamic nature and hostile environment of a working CHFS reactor.

Local structure and nanoscale homogeneity of CeO2–ZrO2: differences and similarities to parent oxides revealed by luminescence with temporal and spectral resolution

Although homogeneity at the atomic level of CeO2-ZrO2 with a Ce/Zr atomic ratio close to unity is considered to be one of the main causes for the increased total oxygen storage capacity (OSC), the characterization approaches of homogeneity remain a major challenge. We propose a simple, yet effective method, to assess both structural and compositional homogeneity of CeO2-ZrO2 by using Eu(3+) luminescence measured with time and dual spectral resolution (emission and excitation). For Eu(3+)-CeO2-ZrO2 calcined at 750 °C, the X-ray diffraction, Raman and High-Resolution Transmission Electron Microscopy data converge to a single pseudo-cubic phase. However, the evolution of Eu(3+)-delayed luminescence from cubic ceria-like to tetragonal zirconia-like emission reveals the formation of CeO2- and ZrO2-rich nanodomains and provides evidence for early phase separation. For Eu(3+)-CeO2-ZrO2 calcined at 1000 °C, the emission of Eu(3+) reveals both structural and compositional inhomogeneity. Our study identifies the differences between the local structure properties of CeO2 and ZrO2 parent oxides and CeO2-ZrO2 mixed oxide, also confirming the special chemical environment of the oxygen atoms in the mixed oxide as reported earlier by Extended X-ray Absorption Fine Structure investigations.

Direct Synthesis of Dimethyl Carbonate from Methanol and Carbon Dioxide Over CeO&lt;SUB&gt;2&lt;/SUB&gt;(&lt;I&gt;X&lt;/I&gt;)–ZnO(1−&lt;I&gt;X&lt;/I&gt;) Nano-Catalysts

CeO2(X)-ZnO(1-X) (X = 0, 0.1, 0.3, 0.5, 0.7, 0.9, and 1.0) nano-catalysts were prepared by a co-precipitation method with a variation of CeO2 content (X, mol%), and they were applied to the direct synthesis of dimethyl carbonate from methanol and carbon dioxide. Successful formation of CeO2(X)-ZnO(1-X) nano-catalysts was well confirmed by XRD analysis. The amount of DMC produced over CeO2(X)-ZnO(1-X) catalysts exhibited a volcano-shaped curve with respect to CeO2 content. Acidity and basicity of CeO2(X)-ZnO(1-X) nano-catalysts were measured by NH3-TPD and CO2-TPD experiments, respectively, to elucidate the effect of acidity and basicity on the catalytic performance in the reaction. It was revealed that the catalytic performance of CeO2(X)-ZnO(1-X) nano-catalysts was closely related to the acidity and basicity of the catalysts. Amount of dimethyl carbonate increased with increasing both acidity and basicity of the catalysts. Among the catalysts tested, CeO2(0.7)-ZnO(0.3) with the largest acidity and basicity showed the best catalytic performance in the direct synthesis of dimethyl carbonate from methanol and carbon dioxide.

Synthesis and characterization of Pt/Al2O3–CeO2 nanocatalyst used for toluene abatement from waste gas streams at low temperature: Conventional vs. plasma–ultrasound hybrid synthesis methods

To assess the synergism effect of plasma and ultrasound treatment on the physicochemical properties and catalytic performance of supported-Pt nanocatalysts, a series of nanostructured Pt(1wt.%)/Al2O3–CeO2(30wt.%) catalysts were prepared by plasma and/or ultrasound-assisted impregnation methods and tested for the total oxidation of toluene. The nanocatalysts were characterized by XRD, FESEM, FTIR, EDX and N2 adsorption–desorption measurements. XRD data confirmed the formation of CeO2 as the crystalline phase with an average crystallite size of about 8.7nm for all samples. EDX dot mapping indicated homogenous dispersion of elements. The results indicated that the remarkable synergetic effect of ultrasound irradiation on the surface morphology and elemental dispersion, especially when it is coupled with plasma treatment. All treated nanocatalysts showed lower temperature activity and better catalytic performance in toluene oxidation with high stability, in particular, ultrasound–plasma assisted synthesized nanocatalyst exhibited the approximately complete oxidation of toluene at 180°C. It is observed that even at higher concentrations of toluene (3000ppm) or GHSV, plasma–ultrasound assisted synthesized nanocatalyst had still enough destruction ability to reduce the pollutant. Therefore, the plasma–ultrasound hybrid synthesis method can lead to an excellent preparation of supported nanocatalysts, esp., those for VOCs oxidation.

Facile Synthesis of Au/CeO&lt;SUB&gt;2&lt;/SUB&gt; Catalyst for Low Temperature CO Oxidation

Nanosized ceria (CeO2) with high surface area was developed by a single pot combustion synthesis and highly dispersed nanosized gold (∼0.5 wt.% and around 10 nm) on CeO2 was achieved by deposition precipitation (DP) method. X-ray diffraction confirmed the formation of CeO2, whereas transmission electron microscope ensured the presence of nanosized CeO2 and gold particles. Physico-chemical studies by UV-Vis, Raman and X-ray photoelectron spectroscopy indicated the coexistence of gold and cerium in mixed oxidation states, whereas temperature programmed reduction confirmed the high amount of surface oxygen groups on Au/CeO2-DP (DP of Au on CeO2 where CeO2 prepared by Mixed fuel such as citric acid + Urea) and Au/CeO2-CB (Entire Au/CeO2 catalyst prepared by citric acid combustion) catalysts. Typical results during CO oxidation indicated the high rate (35 mole CO g–1 Au h–1 and 18 mole CO g–1 Au h–1 at 313 K) and low activation energy (E a) (15 kJ mol–1 and 17 kJ mol–1) with Au/CeO2 (DP) and Au/CeO2 (CB) catalysts respectively.

Ce-substituted LaNiO3 mixed oxides as catalyst precursors for glycerol steam reforming

Mixed oxides of general formula La1−xCexNiO3 were prepared by self-combustion method and taken as precursors of Ni-supported catalysts for an experimental investigation of steam reforming of glycerol. The mixed oxide precursors and the corresponding derived fresh catalysts were characterized by XRD, TPR and TEM while the used catalysts were investigated by FE-SEM, TEM and TPO/TGA-MS. All catalysts were investigated on glycerol steam reforming with special focus on the resistance to deactivation. The precursors led to active catalysts, producing hydrogen-rich gas stream. Deactivation was seen to occur irrespective of catalyst composition. Substitution of 50% La by Ce provided more deactivation-resistant catalyst, allowing only minor amount of more reactive carbon deposits. It was suggested to be associated with the formation of CeO2–La2O3 solid solutions, as evidenced by XRD, which would act as an oxygen buffer and therefore facilitate the removal of carbon deposits onto the catalyst surface.

Studies on the improved thermal stability for doped ordered mesoporous γ-alumina

Ordered mesoporous γ-alumina (OMA), Ce-doped, Zr-doped and Ce-Zr-codoped OMA samples were synthesized in a sol-gel system with P123 as the soft template, both salicylic acid and citric acid as the assistant templates. The results show that the incorporations of either cerium or zirconium or both are able to improve the thermal stability of OMA. The capability to preserve the structural ordering and suppress the phase transition from γ-Al2O3 to α-Al2O3 at high temperature observed on the doped OMA is due to the formation of CeO2, ZrO2 or Ce(x)Zr(1-x)O2 phase, which is capable of protecting OMA from the structural collapse by sintering and phase transition.

Synthesis and physicochemical characterization of nanostructured CeO2/clinoptilolite for catalytic total oxidation of xylene at low temperature

A series of nanostructured CeO2/Clinoptilolite catalysts with different loadings of ceria were prepared by redox reaction followed by wet impregnation method and tested for oxidation of xylene. The catalysts were characterized by XRD, FESEM, BET, FTIR, and TG‐DTG analysis. XRD data confirmed the formation of CeO2 as the crystalline phase with an average crystallite size of about 11.6 nm for three ceria loading of 10, 20, and 30%. FESEM and size distribution analyses showed that nanocatalysts have nanometric particles with an average size of 37.46 nm. Specific surface analysis revealed that the synthesized nanocatalysts had large enough surface area for catalytic oxidation of p‐xylene. Furthermore, the results showed that the catalytic performance of the supported CeO2 catalysts was much higher than that of treated clinoptilolite, in particular, CeO2 (30%)/Clinoptilolite exhibited the highest conversion, 98% at 350°C. It is observed that increasing both the xylene concentration and GHSV results in decreasing of the xylene conversion; however, even at higher concentrations of xylene (3000 ppm), the nanostructured catalyst has still enough destruction ability to reduce the pollutant. A simplified reaction mechanism was proposed with respect to the behavior of adsorbed species on the catalyst surface to clarify the path through which the reaction components interact with each other. © 2012 American Institute of Chemical Engineers Environ Prog, 32: 587–597, 2013

The Preparation and Structure Characterization of Nano-Alumina Fiber Doped Cerium by Electrospinning

Alumina fiber, a kind of inorganic fiber, was widely used in many fields owing to its excellent performance. CeCl3/AlCl3/PVP was used as spinning solution for producing organic-inorganic hybrid fiber by electrospinning, then, alumina fiber doped cerium can be successfully obtained after high temperature calcination. In the paper, the influence of CeCl3 to the crystallization and thermal stability was discussed. The results show that alumina nanofiber with average diameters of 200nm-800nm are obtained by calcination of the as-prepared fibers .The addition of CeCl3 significantly delay the crystallization transformation process of alumina fiber, while the formation of CeO2 reduce diffusion rate of Al3+, eventually, imped the phase transformation of Al2O3 and improve its thermal stability.

An analysis of the first steps of phenol adsorption-oxidation over coprecipitated Mn–Ce catalysts: a DRIFTS study

A series of Mn–Ce(M) solids (M = K or Na), with molar ratios 100–0, 50–50 and 0–100 were prepared by co-precipitation of manganese and cerium nitrate from NaOH or KOH solutions at pH = 11. In addition, part of the solids precipitated with NaOH were dried and impregnated with a Cu2+ salt. The solids were characterized by XRD, Specific Surface Area, XPS and EDS. The characterization analyses show the formation of Mn mixed oxides with different oxidation states (Mn3+, Mn4+), for samples without Ce or Mn–Ce(M) 50–50. In the latter solid and in the one where there is no Mn, the formation of CeO2 (fluorite type) was detected. The samples were tested in the phenol removal in water at 100 °C and at atmospheric pressure with the aim to analyze the adsorbed species in the first stage of the adsorption-oxidation mechanisms. The results indicate, on the one hand, that [MnOx] is the active species in the process and that the most active solids are those that present (i) a higher concentration of OI, (ii) a higher amount of Mn4+ ions. DRIFT spectroscopy showed a possible mechanism of phenol adsorption on two sites, in the first one by H interaction of OH (phenol) with an OH of the catalyst and in the second, by the formation of a phenolate species between an O (OH phenol) and Mnn+.

In situ characterization of Ptcatalysts supported on ceria modified TiO2 for the WGS reaction: influence of ceria loading

This work analyzes the influence of cerium content (6-15 wt%) on a TiO(2) support over the structure and water gas shift (WGS) activity of Pt catalysts. The structural properties of these Pt/Ce-TiO(2) catalysts were characterized by XRD, TEM and XANES. Physicochemical characterization of the catalysts showed differences in the structure and dispersion of Ce entities on the support with Ce loading. For the samples with low ceria content (6 wt%), cerium is deposited on the support in the form of CeO(x) clusters in a highly dispersed state in close interaction with the Ti atoms. The formation of CeO(x) clusters at low Ce-loading on the support facilitates the dispersion of small particles of Pt and improves the reducibility of ceria component at low temperatures. The changes in platinum dispersion and support reducibility with Ce-loading on the TiO(2) support lead to significant differences in the WGS activity. Pt supported on the sample with lower Ce content (6 wt%) shows better activity than those corresponding to catalysts with higher Ce content (15 wt%). Activity measurements coupled with catalysts characterization suggest that the improvement in the reducibility of the support with lower Ce content was associated with the presence of CeO(x) clusters of high reducibility that improve the chemical activity of the oxide-metal interfaces at which the WGS reaction takes place.

China rose petal as biotemplate to produce two-dimensional ceria nanosheets

China rose petal was used as robust biotemplate for the facile fabrication of novel ceria nanosheet with a thickness of about 7 nm via a continuous infiltration process. The presence of well-resolved peaks ([111], [200], [220], and [311]) for the products revealed the formation of the fluorite-structured CeO2. The detailed characterization by field-emission scanning electron microscope (FESEM), field-emission transmission electron microscope (FETEM), and atomic force microscopy (AFM) exhibited the biomorphic structure of polycrystalline ceria film with the nanoparticle size of ca. 6.98 nm. Based on the surface chemistry and biochemistry processes, a possible mechanism for the formation of CeO2 nanosheets is proposed. Furthermore, nitrogen adsorption–desorption measurement and photoluminescence spectrum (PL) were employed to characterize the samples. The ceria nanosheet showed the existence of mesopores (pores 2–4 nm diameter) on its surface and a broad emission ranging from 350 to 500 nm in photoluminescence spectrum. X-ray photoelectron spectroscopy analysis (XPS) confirmed that the mesoporous nanosheets possessed more surface vacancies than the bulk CeO2; hence these hierarchical CeO2 layers appear to be potential candidates for catalytic applications.