Mixed Oxide Samples Research Articles

Synergy of iron and copper oxides in the catalytic formation of PCDD/Fs from 2-monochlorophenol

Transition metal oxides present in waste incineration systems have the ability to catalyze the formation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) through surface reactions involving organic dioxin precursors. However, studies have concentrated on the catalytic effects of individual transition metal oxides, while the complex elemental composition of fly ash introduces the possibility of synergistic or inhibiting effects between multiple, catalytically active components. In this study, we have tested fly ash surrogates containing different ratios (by weight) of iron (III) oxide and copper (II) oxide. Such Fe2O3/CuO mixed-oxide surrogates (in the Fe:Cu ratio of 3.5, 0.9 and 0.2 ) were used to study the cooperative effects between two transition metals that are present in high concentrations in most combustion systems and are known to individually catalyze the formation of PCDD/Fs. The presence of both iron and copper oxides increased the oxidative power of the fly ash surrogates in oxygen rich conditions and led to extremely high PCDD/F yields under pyrolytic conditions (up to >5% yield) from 2-monochlorophenol precursor. PCDD/F congener profiles from the mixed oxide samples are similar to results obtained from only CuO, however the total PCDD/F yield increases with increasing Fe2O3 content. Careful analysis of the reaction products and changes to the oxidation states of active metals indicate the CuO surface sites are centers for reaction while the Fe2O3 is affecting the bonds in CuO and increasing the ability of copper centers to form surface-bound radicals that are precursors to PCDD/Fs.

Binary oxide ceramics for enhanced phenols degradation under simulated Solar light

AbstractSolvothermal synthesis of ZrO2–TiO2 binary oxides and pure counterparts at 150°C in water/isopropanol media is presented. Titanium (IV) isopropoxide and zirconium (IV) propoxide were used as precursors. XRD and TEM techniques were used for structural and morphological characterization of obtained samples. XPS spectra of mixed oxide samples were compared in order to correlate composition of samples with surface properties and presence of defects. Relative positions of defect states within band‐gaps of semiconductors were estimated from UCPL spectra. UV‐Vis DRS spectra revealed that both pure oxides experienced red shift of absorption thresholds compared to reference data. Photocatalytic activities of all samples were probed under simulated Solar light on three model compounds: phenol, 4‐chlorophenol (4‐CP) and 2, 4, 6‐trichlorphenol (TCP). Pure TiO2 showed the highest photocatalytic activity in the case of phenol. However, pure ZrO2 and binary oxides showed higher photoactivity in degradation of 4‐CP and TCP. The activity of wide band‐gap semiconductors under simulated Solar light in photodegradation of phenol and its derivatives is most probably the consequence of formation of charge transfer complexes between pollutant molecules and semiconductors surface.

Insights on hydride formation over cerium-gallium mixed oxides: A mechanistic study for efficient H2 dissociation

A four-step reaction mechanism is proposed for the H2 dissociation over pure ceria and gallium-promoted mixed oxide materials, in a combined experimental and computational investigation. Two samples of cerium-gallium mixed oxides with Ce/Ga atomic ratios equal to 90/10 and 80/20 were studied by time-resolved diffuse reflectance infrared spectroscopy under H2 (D2) flow at isothermal condition in the range of 523–623K. X-ray photoelectron spectrometry allowed to conclude that only Ce4+ is reduced to Ce3+ (Ga3+ is not reduced), in agreement with density functional theory (DFT) results. The time evolution profiles of gallium hydride (GaH) species, hydroxyl groups (OH) and Ce3+ infrared signals were analyzed and kinetic rate parameters for each step were obtained by mathematical modeling. The values for activation energies were in agreement with those calculated by DFT, for the different elementary pathways. A small activation energy (∼4kcal/mol) was found for H2 dissociation found on Ga⋯OCe sites assuming that the heterolytic cleavage of the HH bond is the rate determining step. On pure ceria, the experimental activation energy is ∼23kcal/mol, showing that the addition of Ga3+ cations boosts the splitting of H2. Interestingly, the reduction step of pure CeO2 surface domains seems to proceed via a CeH/OH pair intermediate, according to DFT calculations. Moreover, 71Ga NMR experiments indicate the possible presence of gallia nanodomains. It is proposed that the generation of Ga⋯OCe sites in the perimeter of such surface gallia nanodomains is responsible for the enhanced reactivity of the mixed materials. The key role of this new type of sites to improve the efficiency of relevant catalytic reactions such as selective alkyne hydrogenation and light alkane dehydrogenation is then analyzed.

Digital pile-up rejection for plutonium experiments with solution-grown stilbene

A solution-grown stilbene detector was used in several experiments with plutonium samples including plutonium oxide, mixed oxide, and plutonium metal samples. Neutrons from different reactions and plutonium isotopes are accompanied by numerous gamma rays especially by the 59-keV gamma ray of 241Am. Identifying neutrons correctly is important for nuclear nonproliferation applications and makes neutron/gamma discrimination and pile-up rejection necessary. Each experimental dataset is presented with and without pile-up filtering using a previously developed algorithm. The experiments were simulated using MCNPX-PoliMi, a Monte Carlo code designed to accurately model scintillation detector response. Collision output from MCNPX-PoliMi was processed using the specialized MPPost post-processing code to convert neutron energy depositions event-by-event into light pulses. The model was compared to experimental data after pulse-shape discrimination identified waveforms as gamma ray or neutron interactions. We show that the use of the digital pile-up rejection algorithm allows for accurate neutron counting with stilbene to within 2% even when not using lead shielding.

Betterment in EDXRF analytical results for compositional characterization of mixed uranium thorium oxide samples with bead specimens compared with pressed pellet specimens

A comparative study on the energy dispersive X‐ray fluorescence analytical results of uranium determinations, in uranium and uranium–thorium mixed oxides, using specimens in the form of fused beads and pressed pellets, has been made. It was observed that in case of fusion bead specimens, the intensity of the analyte lines was approximately 1.6 times of that observed in pellet specimens under identical instrumental conditions. In case of uranium oxide samples, the analytical results with bead specimens were slightly better compared with the pellet specimens. However, in case of the uranium–thorium oxide mixtures, the average precision obtained with bead specimen was significantly better (1%, 1 s) in comparison with that achieved using pellet specimens (7%, 1 s). This difference may be due to the hardness of thorium oxide compared with uranium oxide, which affects the homogeneity of the pellet specimens prepared. In fusion bead method of sample preparation, even highly refractory material like ThO2 forms uniform glass beads. Addition of internal standard further improves the analytical results, with reduction in the percent deviation of energy dispersive X‐ray fluorescence results from the expected values to 3% from 7% compared with that obtained using without internal standard. The fusion bead method of sample preparation will be very useful for characterization of sintered (U,Th)O2 pellets, which are highly refractory and difficult to dissolve. Copyright © 2016 John Wiley & Sons, Ltd.

Photocatalytic Degradation of Oxytetracycline Using Co-precipitation Method Prepared Fe2O3/TiO2Nanocomposite

Fe₂O₃/TiO₂ nanocomposite were successfully synthesized by co-precipitation method using Fe (NO₃)₃·9H₂O and Ti (SO₄)₂ as raw materials. Structural and textural features of the mixed oxide samples were characterized by X-ray diffractometer, field emission scanning electron microscopy and energy-dispersive X-ray. The effects of initial concentration of oxytetracycline (OTC), different competitive ions and organics on the photocatalytic degradation rate of OTC by the Fe₂O₃/TiO₂ nanocomposite were analyzed under UV and visible light irradiation. The results indicate that the optimized initial concentration of OTC was 50 ㎎/L to achieve the best photocatalytic efficiency. Cu 2+ , NH₄⁺, C₃H₈O and EDTA in the aqueous suspension were found to suppress the degradation rate of OTC, whereas the effect of NO₃⁻ and H₂C₂O₄ can be ignored.

Structural optical correlated properties of SnO2/Al2O3 core@ shell heterostructure

Nano size polycrystalline samples of the core@shell heterostructure of SnO2 @ xAl2O3 (x = 0, 25, 50, 75 wt.%) were synthesized by sol–gel technique. The resulting samples were characterized with fourier transform infrared spectroscopy (FT-IR), photoluminescence (PL) and X-ray powder diffraction (XRD). The XRD patterns manifest diffraction peaks of SnO2 as main phase with weak peaks corresponding to Al2O3 phase. The formation of core@ shell structure is confirmed by TEM images and Rietveld quantitative phase analysis which revealed that small part of Al2O3 is incorporated into the SnO2 lattice while the main part (shell) remains as a separate phase segregated on the grain boundary surface of SnO2 (core). It is found that the grain size of the mixed oxides SnO2 @ xAl2O3 is below 10 nm while for pure SnO2 it is over 41 nm, indicating that alumina can effectively prevent SnO2 from further growing up in the process of calcination. This is confirmed by the large increase in the specific surface area for mixed oxide samples. The PL emission showed great dependence on the structure properties analyzed by XRD and FTIR. The PL results recommend Al2O3@SnO2 core@shell heterostructure to be a promising short-wavelength luminescent optoelectronic devices for blue, UV, and laser light-emitting diodes.

Biphasic MO2+x-M3O8-z domain of the U-Pu-O phase diagram.

The reduction of six mixed-oxide samples containing 14, 24, 35, 46, 54, and 62 mol % Pu was studied in situ by X-ray diffraction. The samples were first oxidized in air and subsequently reduced in a controlled atmosphere corresponding to a stoichiometric composition with an O/M = 2.00. After oxidation, we observed two structures, one cubic and one orthorhombic, MO2+x and M3O8-z. The two phases were subsequently reduced back to their stoichiometric O/M = 2.00 in a controlled atmosphere. The plutonium contents of the two resulting cubic structures differed from the initial one. We conclude that strong cation transport took place during oxidation, according to the shape of the tie lines in the biphasic MO2+x/M4O9-M3O8-z domain. The resulting overall O/M after oxidation was estimated. We propose the shape of the tie lines in the aforementioned biphasic domain and suggest a maximal plutonium solubility in the M3O8 structure at 8 ± 2 mol % (Pu/U + Pu) at 1573 K.

The Applications of Mixed Metal Oxides to Capture the CO2 and Convert to Syn-Gas

The applications of different mixed metal oxides were explored for the capture of CO2 and convert of CO2 to syn-gas. The several samples of the mixed metal oxides were prepared by the sol-gel, solid-solid fusion, precipitation, molten salt and template methods in order to investigate the performance of mixed mtal oxides to the CO2 applications. These samples were calcined for the 3 h in air at 900 oC. The mixed metal oxides samples were characterized by acidity/basicity, surface area, XRD pattern, SEM images and to capture CO2. The basicity and surface area of the samples of mixed metal oxides were found to be in the range from 0.7 to 15.7 mmol.g-1 and 2.24 to 138.76 m2.g-1, respectively. The ob-tained results of prepared mixed metal oxides by different method were compared for the purpose of searching the efficient materials. The temperature profiles of the captured CO2 by the samples of mixed metal oxides were obtained in the range 100 to 800 oC. The captured CO2 was found to be in the range from 7.36 to 26.93 wt.%. The conversions of CO2 by methane were explored to syn-gas over the mixed metal oxides including the calcium iron lanthanum mixed metal oxides and (5 wt.%) Pd/Al2O3 at 700 oC with the gas hourly space velocities (GHSV) 6000 ml.h-1.g-1 of methane, 6000 ml.h-1.g-1 of CO2 and 24000 ml.h-1.g-1 of helium. © 2015 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0)

Angular-resolution and material-characterization measurements for a dual-particle imaging system with mixed-oxide fuel

A dual-particle imaging (DPI) system, capable of simultaneously imaging fast neutrons and gamma rays, has been operated in the presence of mixed-oxide (MOX) fuel to assess the system׳s angular resolution and material-characterization capabilities. The detection principle is based on the scattering physics of neutrons (elastic scattering) and gamma rays (Compton scattering) in organic and inorganic scintillators. The detection system is designed as a combination of a two-plane Compton camera and a neutron-scatter camera. The front plane consists of EJ-309 liquid scintillators and the back plane consists of interleaved EJ-309 and NaI(Tl) scintillators. MCNPX-PoliMi was used to optimize the geometry of the system and the resulting prototype was built and tested using a Cf-252 source as an SNM surrogate. A software package was developed to acquire and process data in real time. The software was used for a measurement campaign to assess the angular resolution of the imaging system with MOX samples. Measurements of two MOX canisters of similar isotopics and intensity were performed for 6 different canister separations (from 5° to 30°, corresponding to distances of 21cm and 131cm, respectively). The measurements yielded a minimum separation of 20° at 2.5m (86-cm separation) required to see 2 separate hot spots. Additionally, the results displayed good agreement with MCNPX-PoliMi simulations. These results indicate an angular resolution between 15° and 20°, given the 5° step. Coupled with its large field of view, and its capability to differentiate between spontaneous fission and (α,n) sources, the DPI system shows its potential for nuclear-nonproliferation applications.

Feedback on 239Pu and 240Pu nuclear data and associated covariances through the CERES integral experiments

Benchmark measurements of irradiated and un-irradiated fuel samples were performed in the framework of the CERES collaborative program between AEA (UK Atomic Energy Agency) and CEA (French Atomic Energy Commission). These experiments provide relevant data for the validation of fuel burn-up and criticality-safety calculations for the whole fuel cycle. As part of this program, pile-oscillation measurements were carried out on a range of mixed-oxide samples with plutonium of various mass and isotopic contents, both in the MINERVE and DIMPLE reactors. Four core configurations, two over-thermalized situations and two pressurized water reactor (PWR)-type situations, were constituted with different forward and adjoint flux spectra, emphasizing fission and/or capture contributions. The experiments were analyzed using reference TRIPOLI4 calculations with the JEFF-3.1.1 library, using exact three-dimensional models of the core configurations. In a first step, calculations of each DIMPLE configuration were performed and compared with the experiment, showing very good agreements with a maximum C-E of −230 pcm. In the second step, reactivity worth experiments were analyzed, using recently developed exact-perturbation capabilities in TRIPOLI4. A consistent assimilation of calculation over experiment discrepancies was performed with the CONRAD code, using the integral data assimilation method. Covariance matrix on multigroup neutron cross sections and multiplicities were generated and significant trends were identified, especially on the 239Pu and 240Pu capture cross sections in the thermal energy range (E < 0.1 eV). Further investigations should be required to confirm these conclusions, due to the strong dependence of these trends and of posterior covariances to prior covariances.

Effect of preparation procedure on the formation of nanostructured ceria–zirconia mixed oxide catalysts for ethyl acetate oxidation: Homogeneous precipitation with urea vs template-assisted hydrothermal synthesis

Two series of ceria–zirconia mixed oxide samples with wide variation in the composition were synthesized using homogeneous precipitation with urea and template-assisted hydrothermal procedures. The samples were characterized by nitrogen physisorption, XRD, SEM, Raman, XPS, UV–vis, FTIR, pyridine-FTIR and TPR techniques. The catalytic activity in ethyl acetate total oxidation as a representative of VOCs was tested. The effect of preparation procedure on the texture, structure, morphology, acidic and redox properties was discussed in details in close relation with mixed oxides composition and possibilities for fine tuning of their catalytic activity. As compared to urea procedure, the hydrothermal treatment provides more homogeneous insertion of Zr ions within cubic ceria lattice even at high Zr content. As a result higher degree of distortion of the cubic lattice, creation of Ce3+ and oxygen vacancies and an increase in both Lewis acidity and redox ability is observed and these properties are not affected by the presence of template during the synthesis. The differences in the redox and surface acidic properties of both series of materials probably promote the realization of the catalytic process by various reaction pathways and thus influence in a complex way the catalytic activity and selectivity.

Non-aqueous route spray pyrolyzed Ru:Co3O4 thin electrodes for supercapacitor application

Spray pyrolytic deposition of ruthenium incorporated cobalt oxide thin film electrodes was carried out via methanolic route at 623±2K. Structural, morphological, optical, compositional and electrochemical study was made using XRD, SAED, SEM, TEM, UV–vis, EDX, XPS and electrochemical work station. Deposited samples shows face centered cubic crystal structure for Co3O4 and tetragonal for RuO2 having crystalline nature was confirmed form SAED. Mixed oxide samples having porous nano-grain morphology and mixed microstructure as observed form SEM and TEM. Cyclic voltammogram study reveals double-pseudo-capacitive nature with optimum specific capacitance (SC) 628.33F/g at the scan rate 1mV/s in 1M KOH with good stability. Charge–discharge behavior was studied to calculate electric parameters such as specific energy (SE), specific power (SP) and columbic efficiency (η). The calculated maximum values are SE 19.94Wh/kg, SP 5.33kW/kg and η 99.43%. Electrochemical impedance study was made in the frequency range 1mHz to 1MHz to see the internal resistance and capacitive behavior of the optimized sample. The randles equivalent circuit and its parameters are reported in the text.

Activity of MnOx–CeO2 catalysts in combustion of low concentrated methane

Due to its warming potential over 20 times higher than that of CO2, methane is classified as one of the most dangerous pollutants. Removal of methane emitted particularly from low calorific sources, such as coal mine ventilation air streams or dumping grounds, falls thus in line with the most important challenges of environmental catalysis. Main goal of this work was to verify the efficiency and to understand the catalytic behavior of a series of coprecipitated MnOx–CeO2 mixed oxide samples, containing nominally 30–80mol% of MnO2. A plethora of structural (XRD, RS), textural (BET), and spectroscopic (EPR, XPS, and RS) methods have been applied for sample characterization. Catalytic activity has been determined by TPSR in the temperature range from 100 to 700C. It was shown that catalytic activity of the investigated MnOx–CeO2 samples is strongly related to their structural heterogeneity and reducibility of various manganese centers coexisting within the surface MnOx clusters interacting with nanocrystalline CeO2.

Hydroxylation of benzene to phenol over magnetic recyclable nanostructured CuFe mixed-oxide catalyst

A highly active and magnetically recyclable nanostructured copper–iron oxide (CuFe) catalyst has been synthesized for hydroxylation of benzene to phenol under mild reaction conditions. The obtained catalytic results were correlated with the catalyst structure, which was characterized by XRD, SEM, TEM, EDX, H2-TPR and BET. The catalytic results indicated that the CuFe mixed oxide samples exhibited superior performance compared to its analogous single nano-oxide catalysts. The influence of the reaction condition variables, such as the solvent, reaction temperature, time, and amount of H2O2 oxidant, were investigated. Under optimized conditions, CuFe resulted in benzene conversion of 44% at a phenol selectivity of 91% and a corresponding combined hydroquinone/catechol/benzoquinone selectivity of 9%. In addition, the catalytic activity of the nano-oxide CuFe was significantly affected by the different calcination temperatures due to the induced catalyst structure, which was confirmed by the characterization results. This enhanced activity was due to the structural phases and redox modification resulting from the interface between the Cu and Fe metals, which was caused by varying calcination temperatures. The activity of CuFe does not require the formation of the typical favored CuFe2O4 spinel to achieve a highly active catalyst, which results from the enhanced redox potentials. CuFe is highly recyclable due to its magnetic nature, which results in an excellent ecofriendly catalyst for the direct synthesis of phenol from benzene hydroxylation.

Óxidos Mistos de Al2O3/ZrO2 como Inibidores de Corrosão do Aço SAE 1020

This paper describes the use of Al 2 O 3 /ZrO 2 mixed oxides synthesized by sol-gel process with different amounts of ZrO 2 (5%, 10%, 15% and 20% by mass) in the Al 2 O 3 matrix and different temperatures of calcination, such as interesting inhibitor materials of corrosive processes of SAE 1020 steel. The materials were characterized by Infrared Spectroscopy Fourier Transform (FTIR) and X-Ray Diffraction (XRD) techniques. FTIR spectra show the typical Al-O and Zr-O bonds vibrations in the mixed oxides. The XRD patterns of the samples calcined at 800 °C and 1000 °C shows the ZrO 2 tetragonal and γ-Al 2 O 3 face-centered cubic (FCC) phases. The corrosion tests showed that the SAE 1020 steel covered with mixed oxides have an anodic passive region, thereby inhibiting the corrosive processes on the metal surface. Furthermore, the found values for steel coated with mixed oxide synthesized indicate a decrease in corrosion potentials (E cor ) and corrosion current (i cor ). With respect to different samples of mixed oxides, the sample with 20 % of ZrO 2 in the Al 2 O 3 matrix proved to be the best inhibitor of steel corrosion, with the lowest values of corrosion potential and corrosion current, - 1.32 V and 0.31 μA cm -2 , respectively.

The role of the suprastoichiometric molybdenum during methanol to formaldehyde oxidation over Mo–Fe mixed oxides

Iron molybdates are common industrial catalysts for methanol oxidation. The role of Mo excess, usually present in the catalyst formulation still doubtful. Some authors claim a stability effect whereas others claim that surface MoO3, segregated from bulk, is the active phase.In order to clarify the role of Mo excess on the catalytic performances, catalysts were prepared by Mo surface loading of stoichiometric Fe2(MoO4)3. No crystalline MoO3 was detected even for the sample prepared with five monolayers (maximum number) of MoO3. XPS data reveals a Mo surface enrichment even for the stoichiometric mixed oxide sample. All the samples presented Mo/Fe atomic ratio higher than the stoichiometric value (1.5). Adding of MoO3 monolayers seems to promote surface aggregation of Mo species.Catalytic data showed that Mo surface enrichment of the stoichiometric phase leads to an increase of formaldehyde yield for loadings higher than 0.5 monolayers. The observed behavior seems to result from a compromise between the higher catalytic activity of the Fe2(MoO4)3 phase and the lower activity but higher selectivity of the MoO3 phase. A cooperative effect between the MoO3 and the molybdate phase seems to dictate the catalytic performances.

Photo and radiation induced synthesis of (Ni, Zn)O or mixed NiO–ZnO oxides

A set of mixed oxide samples containing crystalline NiO–ZnO with variable composition was prepared by irradiation of aqueous solutions containing nickel and/or zinc nitrate hexahydrate, with subsequent heat treatment. Due to irradiation, either by accelerated electrons or UV light, weakly crystalline solid precursor was formed. After heat treatment at temperatures of 300 °C or higher, nanocrystalline NiO, ZnO and mixture of ZnO and solid solution (Ni, Zn)O were formed, with different amounts of nickel or zinc. Photo or radiation induced synthesis yielded material with quality nanocrystals (from one to twenty nm) and very high specific surface area.

Determining surface composition of mixed oxides with pH

In this study we have developed a 2-surface model with the EPHL (“Equilibrium pH at high oxide loading”) method for mixed and composite oxides. Oxide charging parameters, namely the protonation and deprotonation constants and the hydroxyl surface densities, can be established from measurements of the pure oxides and used in the 2-surface model to predict the point of zero charges (PZC) of mixed and composite oxides. The accuracy of these predictions has been demonstrated with diverse control samples of known surface composition (physical mixtures of silica and alumina of high and low surface area). The EPHL method has been extended to composite materials (bound catalysts) and can explain correlations of reactivity with catalyst surface composition. The “apparent surface coverage” (ASC) of a particular mixed or composite oxide sample may then be determined by comparing the PZC of the material to either the 2-surface model results, using parameters of the individual oxides, or a calibration curve of EPHL measurements of physical mixtures of the individual ingredients.

Mesoporous cerium oxide nanospheres for the visible-light driven photocatalytic degradation of dyes.

A facile, solvothermal synthesis of mesoporous cerium oxide nanospheres is reported for the purpose of the photocatalytic degradation of organic dyes and future applications in sustainable energy research. The earth-abundant, relatively affordable, mixed valence cerium oxide sample, which consists of predominantly Ce7O12, has been characterized by powder X-ray diffraction, X-ray photoelectron and UV–vis spectroscopy, and transmission electron microscopy. Together with N2 sorption experiments, the data confirms that the new cerium oxide material is mesoporous and absorbs visible light. The photocatalytic degradation of rhodamin B is investigated with a series of radical scavengers, suggesting that the mechanism of photocatalytic activity under visible-light irradiation involves predominantly hydroxyl radicals as the active species.