Composition Of Mixed Oxides Research Articles

Gold-Based Catalysts for Complete Formaldehyde Oxidation: Insights into the Role of Support Composition

Formaldehyde (HCHO) is recognized as one of the most emitted indoor air pollutants with high detrimental effect on human health. Significant research efforts are focused on HCHO removal to meet emission regulations in an effective and economically profitable way. For over three decades, the unique electronic properties and catalytic abilities of nano-gold catalysts continue to be an attractive research area for the catalytic community. Recently, we reported that mechanochemical mixing is a relevant approach to the preparation of Co-Ce mixed oxides with high activity in complete benzene oxidation. A trend of higher surface defectiveness, in particular, oxygen vacancies, caused by close interaction between cobalt oxide and cerium oxide phases, was observed for a mixed oxide composition of 70 wt.% Co3O4 and 30 wt.% CeO2. These results directed further improvement by promotion with gold and optimization of mixed oxide composition, aiming for the development of an efficient catalyst for room temperature HCHO abatement. Support modification with potassium was studied; however, the K addition caused less enhancement of HCHO oxidation activity than expected. This motivated the preparation of new carrier material. In addition to Co3O4-CeO2 mixed metal oxides with preset ratio, γ-Al2O3 intentionally containing 33% boehmite and shortly named Al2O3-b was used for synthesis. Analysis of the role of support composition in HCHO oxidation was based on the characterization of nano-gold catalysts by textural measurements, XRD, HRTEM, XPS, and TPR techniques. Gold supported on mechanochemically treated Co3O4-CeO2-Al2O3-b (50 wt.% Al2O3-b) exhibited superior activity owing to high Ce3+ and Co3+ surface amounts and the most abundant oxygen containing species with enhanced mobility. This catalyst achieved oxidation to CO2 and H2O by 95% HCHO conversion at room temperature and 100% at 40 °C, thus implying the potential of this composition in developing efficient catalytic materials for indoor air purification.

Mixed metal oxide Bi2O3/Bi2WO6 thin films for the photoelectrocatalytic degradation of histamine

Photoelectrocatalytic technologies emerge as competitive strategy to manage increasing histamine concentrations. This work explores the synergistic benefits induced in the formation of mixed oxide semiconductor in solid solution. Photoelectrocatalytic films of Bi2O3, WO3, and their hybrid metal mixed oxide composition Bi2O3/Bi2WO6 were synthesized and characterized. Results demonstrate that Bi2O3/Bi2WO6 structure increases stability of charge carriers and enhances degradation performance. Applied bias potential was identified as driving variable that induces effective charge carrier stabilization for accelerated degradation of histamine in aqueous solution. Scavenger experiments identified •OH and O2•- as the main oxidant species produced during photoelectrocatalytic treatment.

Capabilities of Grazing Incidence X-ray Diffraction in the Investigation of Amorphous Mixed Oxides with Variable Composition.

X-ray Diffraction has been fully exploited as a probe to investigate crystalline materials. However, very little research has been carried out to unveil its potentialities towards amorphous materials. In this work, we demonstrated the capabilities of Grazing Incidence X-ray Diffraction (GIXRD) as a simple and fast tool to obtain quantitative information about the composition of amorphous mixed oxides. In particular, we evidenced that low angle scattering features, associated with local structure parameters, show a significant trend as a function of the oxide composition. This evolution can be quantified by interpolating GIXRD data with a linear combination of basic analytical functions, making it possible to build up GIXRD peak-sample composition calibration curves. As a case study, the present method was demonstrated on Ta2O5–SiO2 amorphous films deposited by RF-magnetron sputtering. GIXRD results were validated by independent measurement of the oxide composition using Rutherford Backscattering Spectrometry (RBS). These materials are attracting interest in different industrial sectors and, in particular, in photovoltaics as anti-reflection coatings. Eventually, the optical properties measured by spectroscopic ellipsometry were correlated to the chemical composition of the film. The obtained results highlighted not only a correlation between diffraction features and the composition of amorphous films but also revealed a simple and fast strategy to characterize amorphous thin oxides of industrial interest.

Mixed metal oxides as efficient electrocatalysts for water oxidation

Water splitting is a promising reaction for storing sustainable but intermittent energies. The critical bottleneck for it is oxygen evolution reaction (OER) requiring insufficiently low overpotentials, η. Metal oxides are the group of high performance catalysts for water oxidation, so far. We report a facile synthesis of the mixed metal oxide composite (NiO/Mn-doped NiCo2O4) and an easy dip-coating method to create electrocatalysts on nickel foam as electrode substrates cause significant efficiency for OER. The mixed metal oxides catalyst was characterized by using electrochemical methods, high-resolution transmission electron microscopy (HR-TEM), field emission-scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), inductively coupled plasma (ICP) and fourier-transform infrared spectroscopy (FTIR). Electrocatalysts were shown a Tafel slope of 34 mV dec−1 with overpotential η = 482 mV (for 100 mA cm−2) and at least 20 h durable OER activity. The electrochemical data demonstrate the synergistic effect of the coupling between the three metal-centres of Ni, Co, and Mn to decline the overpotential value. The current of (OER) is related to the electrolyte pH, displaying a non-proton-concerted mechanism in an approach to identifying rate-determining steps for OER. This could be concluded by the direct neighbour lattice O•– coupling to form an O–O bond. The simple and rapid fabrication method and the promising stability and high performance of the herein developed electrodes render them quite promising for technological water splitting systems.

Synthesis, Crystal structure and thermal reactivity of [(N2H5)2Mn0.20Ni0.80(C2O4)2](H2O)2: A novel precursor to nickel-manganese oxide

A novel solid solution precursor, [(N 2 H 5 ) 2 Mn 0.20 Ni 0.80 (C 2 O 4 ) 2 ](H 2 O) 2 has been prepared and characterized by hydrazine analysis, CHN analyses, infrared spectrum, thermal degradation studies and single-crystal X-ray diffraction analysis. The single-crystal X-ray analysis reveals that the complex is centro-symmetric with distorted octahedral geometry. The metal center is occupied by both Mn 2+ and Ni 2+ ions coordinated by four carboxylate oxygen atoms from two bidentate oxalate 2− anions and two axial hydrazinium ions through nitrogen atoms which clearly define the distorted octahedral structure. Simultaneous TG-DTA of the complex shows three steps decomposition resulting in the formation of the mixed metal oxide (MnNi 6 O 8 ) as an end product. The chemical composition of mixed metal oxide obtained was confirmed from energy dispersive X-ray (EDX) data. Atomic force microscopy (AFM) reveals that the nanocomposite is formed as aggregates. The zeta potential (ζ) value is 30.2 mV, which indicates the high stability of the oxide.

Effective remediation of fluoride from drinking water using cerium-silver oxide composite incorporated with reduced graphene oxide

The adsorption capacity of adsorbents towards fluoride removal depends on the component of the adsorption system, such as optimizing parameters, matrix of the adsorbent, and entrapped metal oxides. In the present study, we have developed reduced graphene oxide (rGO)-incorporated cerium‑silver mixed oxide composite (rGO-Ce/Ag) and Ce/Ag bimetallic oxide, for removal of fluoride effectively from the sample solution as well as real water samples. Our aim of this study is to study the effect of rGO matrix on the adsorption capacity of the bimetallic oxide. Both these adsorbents were characterized by FTIR, XRD, TGA/DTA, FESEM, EDX, TEM and BET to understand the physiochemical which had been engaged for defluoridation from aqueous solutions. The results of surface analysis give the surface area of rGO-Ce/Ag and Ce/Ag are 375 and 174 m2/g, respectively which clearly shows that the surface area of rGO-Ce/Ag composite is much higher as compared to the Ce/Ag oxide and hence its adsorption capacity. The adsorption capacity of rGO-Ce/Ag and Ce/Ag are 434.78 and 294.11 mg/g with 99.5 and 95.7% removal, respectively which is consistent with the surface analysis results. Both the adsorbents shows similar adsorption kinetics follows pseudo-second order model and followed Freundlich adsorption isotherm i.e. multilayer type of adsorption mechanism on heterogeneous surface of adsorbent, might be due to same entrapping metals, the matrix only plays the role of enhancing adsorption sites and surface area.

Dual-Site Cooperation for High Benzyl Alcohol Oxidation Activity of MnO2 in Biphasic MnOx–CeO2 Catalyst Using Aerial O2 in the Vapor Phase

Selective oxidation of benzyl alcohol to benzaldehyde in the vapor phase has drawn growing interest recently. In this work, MnOx–CeO2 mixed oxide compositions have been prepared by a coprecipitation method and tested for their oxidation activities of benzyl alcohol to benzaldehyde in the vapor phase. Detailed structural analyses have indicated that MnOx–CeO2 catalysts contain two phases, namely, α-MnO2 and fluorite CeO2 phases. The benzyl alcohol oxidation activity of pure MnO2 is more than 7 times higher compared to that of CeO2, indicating a much higher intrinsic oxidation ability of the MnO2 phase. Further, enhancement of the benzyl alcohol oxidation rate over MnO2 in 10%MnOx–CeO2 catalyst by 13 times is observed in relation to pure MnO2. The role of CeO2 in the MnOx–CeO2 catalyst has also been investigated, which indicates that the oxidation activity is almost independent of CeO2. However, stronger adsorption of benzyl alcohol over the MnOx–CeO2 catalysts compared to that of MnO2 points to the role of CeO2 in adsorption. Thus, both the CeO2 and the MnO2 components have different roles in the catalytic process—adsorption of benzyl alcohol on the CeO2 surface and its oxidation on MnO2 at the interface. The cooperation between the two sites toward oxidation could happen due to jumping of adsorbed benzyl alcohol from the surface of the CeO2 phase to the closest Mn4+ site in the MnO2 phase at the contact surface with MnO2 by thermal motion.

Oxide-oxide galvanic displacement reactions: Effect of the concentration of the ions released by the sacrificial oxide

• Effect of ions released in oxide-oxide galvanic displacement reactions was studied. • Displacement between PbO 2 and Mn 2+ or Co 2+ were used as model reactions. • Secondary mixed oxides produced at higher [Pb 2+ ] were richer in Pb. • Other effects of [Pb 2+ ] on secondary oxide growth depended on divalent cation. Galvanic displacement reactions between a solid oxide and a dissolved metal cation are interesting processes for the preparation of oxide nanoparticles or electrocatalytic layers consisting of secondary mixed oxides. Their mechanism is not yet fully clarified. The composition of the secondary mixed oxides and their growth rate depend on many physical and chemical variables. In the present study, we have focused on the effects of the concentration of the ions released from the sacrificial oxide to the solution, when they are intentionally added to reaction media. We have studied the displacement of sacrificial PbO 2 by either Mn 2+ or Co 2+ cations in acetate solution that contained variable concentrations of Pb 2+ , using electrochemical methods, SEM-EDS and XPS. The evolution of the open circuit potential of the systems was monitored during the reactions. We have found that, for both divalent cations, increasing concentrations of Pb 2+ ions in the acetate solutions caused the formation of mixed oxides richer in Pb. Effects on growth rate and equilibrium potential were different for Mn 2+ and Co 2+ .

Oxidation behaviors and mechanisms of Yb2O3-doped silicon coatings fabricated by vacuum plasma spray

Environmental barrier coatings (EBCs) have been widely studied for the protection of ceramic matrix composites (CMCs). The phase transition of silica thermal growth oxide (TGO) has been proved to be an important factor for the durability of EBCs. Yb2O3 could react with SiO2 TGO and form silicate which may improve the stability of TGO and prolong the service life of EBCs. In the present work, Si coatings doped with different contents of Yb2O3 were fabricated by vacuum plasma spray. The oxidation behaviors of the composite coatings were evaluated at 1350 °C and compared with the pure Si coating. The evolution of phase composition and microstructure of mixed thermal growth oxide (mTGO) was characterized in detail. The results showed that the newly formed oxidation product, namely Yb2Si2O7, could reduce the vertical cracks in mTGO layer and the mTGO/coating interface cracks, leading to a better binding performance of the mTGO layer. The oxidation mechanisms of the Yb2O3-doped Si coatings were analyzed based on microstructure and phase composition observations.

Facet-Dependent Reactivity of Ceria Nanoparticles Exemplified by CeO2-Based Transition Metal Catalysts: A Critical Review

The rational design and fabrication of highly-active and cost-efficient catalytic materials constitutes the main research pillar in catalysis field. In this context, the fine-tuning of size and shape at the nanometer scale can exert an intense impact not only on the inherent reactivity of catalyst’s counterparts but also on their interfacial interactions; it can also opening up new horizons for the development of highly active and robust materials. The present critical review, focusing mainly on our recent advances on the topic, aims to highlight the pivotal role of shape engineering in catalysis, exemplified by noble metal-free, CeO2-based transition metal catalysts (TMs/CeO2). The underlying mechanism of facet-dependent reactivity is initially discussed. The main implications of ceria nanoparticles’ shape engineering (rods, cubes, and polyhedra) in catalysis are next discussed, on the ground of some of the most pertinent heterogeneous reactions, such as CO2 hydrogenation, CO oxidation, and N2O decomposition. It is clearly revealed that shape functionalization can remarkably affect the intrinsic features and in turn the reactivity of ceria nanoparticles. More importantly, by combining ceria nanoparticles (CeO2 NPs) of specific architecture with various transition metals (e.g., Cu, Fe, Co, and Ni) remarkably active multifunctional composites can be obtained due mainly to the synergistic metalceria interactions. From the practical point of view, novel catalyst formulations with similar or even superior reactivity to that of noble metals can be obtained by co-adjusting the shape and composition of mixed oxides, such as Cu/ceria nanorods for CO oxidation and Ni/ceria nanorods for CO2 hydrogenation. The conclusions derived could provide the design principles of earth-abundant metal oxide catalysts for various real-life environmental and energy applications.

Synergistic photocatalytic-adsorption removal effect of NiFe2O4-Zn-Al mixed metal oxide composite under visible-light irradiation

Today, the photocatalytic process in visible light has become one of the most attractive water treatment fields. We prepared a NiFe2O4-MMO composite with Zn-Al LDH and NiFe2O4 that have good photocatalytic properties in visible light. Structural studies on the samples were performed by X-ray diffraction pattern (XRD) analysis and scanning electron microscopy (FE-SEM). Also, diffusion reflection spectroscopy (DRS) analysis was used to evaluate the optical properties of the samples. In this study, the mechanisms of adsorption and photocatalytic processes were investigated. The kinetics of adsorption and photocatalytic processes was also evaluated. The rate of the photocatalytic process is higher than the rate of the adsorption process, so the surface of the photocatalyst is not saturated. As a result, the adsorption process increases the efficiency of the photocatalytic process, which indicates the synergistic effect of adsorption-photocatalytic to improve the process of removal of organic pollutants from contaminated water.

A Generalized Semiempirical Approach to the Modeling of the Optical Band Gap of Ternary Al-(Ga, Nb, Ta, W) Oxides Containing Different Alumina Polymorphs.

A generalization of the modeling equation of optical band gap values for ternary oxides, as a function of cationic ratio composition, is carried out based on the semiempirical correlation between the differences in the electronegativity of oxygen and the average cationic electronegativity proposed some years ago. In this work, a novel approach is suggested to account for the differences in the band gap values of the different polymorphs of binary oxides as well as for ternary oxides existing in different crystalline structures. A preliminary test on the validity of the proposed modeling equations has been carried out by using the numerous experimental data pertaining to alumina and gallia polymorphs as well as the crystalline ternary Ga(1–x)AlxO3 polymorphs (α-Ga(1–x)AlxO3 and β-Ga(1–x)AlxO3) covering a large range of optical band gap values (4.50–8.50 eV). To make a more rigorous test of the modeling equation, we extended our investigation to amorphous ternary oxides anodically formed on Al-d-metal alloys (Al-Nb, Al-Ta, and Al-W) covering a large range of d-metal composition (xd-metal ≥ 0.2). In the last case, the novel approach allows one to overcome some difficulties experienced in fitting the optical band gap dependence from the Al-d-metal mixed anodic oxide composition as well as to provide a rationale for the departure, at the lowest d-metal content (xd-metal < 0.2), from the behavior observed for anodic films containing higher d-metal content.

Синтез и исследование каталитической активности смешанных оксидов цинка и железа для гидротермального облагораживания тяжелой нефти

The effect of the molar ratio of metal cations Zn2 +/Fe3+ in precursors of double hydroxides on the structure of Zn-Fe oxides of mixed phase composition has been established. With an increase in the ratio of metal cations from 1: 1 to 1:4, in the composition of Zn-Fe mixed oxides consisting of oxides ZnO and Fe3O4, the amount of complex oxides ZnFe2O4 with an isomorphic spinel structure decreases, with an increase in the specific surface area from 27.075 to 34.556 m2/d the pore diameter values of 23.8 nm remain constant. The results of experimental studies of the effect of the composition and structure of Zn-Fe mixed oxides on the component composition of heavy oil of naphthenic aromatic base during its upgrading in a hydrothermal fluid at a temperature of 380°C and a pressure of 22 MPa are presented. The maximum increase in the content of saturated hydrocarbons against the background of a noticeable decrease in the amount of asphaltenes is characteristic of hydrothermally converted oil in the presence of mixed oxides Zn-Fe (1: 4), the content of n-alkanes of the composition C10–C14 increases.

Zirconium oxide nanoarrays via the self-organized anodizing of Al/Zr bilayers on substrates

A combination of frontier formation conditions, paradoxical oxide growth, unique ionic transport, a mixed-oxide composition, and phase transition effects resulted in arrays of novel self-assembled zirconium-oxide nanostructures.

Effect of Mixed Oxide Cracking Catalyst on Conversion of the Mixture of Vacuum Gas Oil and Vegetable Oil

A number of cracking catalyst samples containing Me–Mg–Al mixed oxides have been prepared. Cobalt, zinc, copper, and cerium were used as additional metals in the mixed oxide composition. When studying the cracking of a vacuum gas oil–sunflower oil mixture, catalysts containing Co–Mg–Al or Zn–Mg–Al mixed oxides were found to increase both the conversion rate of the mixed feedstock by 5.0 wt % compared to a sample containing the mixed oxide free of additional metal, and the gasoline yield by 1.6–3.0 wt %. It was discovered that the modification of mixed oxides with cobalt or zinc cations has no significant effect on the distribution of inorganic products, thereby indicating sustained catalytic activity during the decarboxylation reaction. The catalytic tests also demonstrated that catalyst samples containing mixed Mg–Al oxides with copper cations exhibited enhanced decarbonylation effect, as well as low conversion rates of the mixed feedstock and low gasoline yield, which is probably associated with the poisoning impact of copper oxide on Y zeolite.

Electrolyte dependent performance of graphene–mixed metal oxide composites for enhanced supercapacitor applications

Graphene–metal frameworks have been extensively studied and developed as electrode materials for next generation energy storage materials. Their high surface area and easily transformable structure enhances its specific capacitance characteristics. In the present study, graphene oxide (GO) was synthesized using Hummers method. Zinc oxide and copper oxide nanoparticles were incorporated in to the GO matrix to form mixed metal oxides. GO, GO–CuO and GO–ZnO were characterized using UV–Visible, FTIR, FT Raman spectroscopy, SEM and XRD to confirm their effective formation. The surface of the glassy carbon electrode was modified by drop casting with the samples on its surface and its electrochemical properties were studied. Cyclic Voltammetry studies were conducted at various scan rates in different electrolytes (KCl, H2SO4 and Na2SO4) and the characteristic curves were observed to be asymmetric in nature. GO–CuO exhibits the highest specific capacitance of 790 F/g at 5 mV/s in KCl. The specific capacitance of the modified electrodes was also measured using the Chronopotentiometry technique. GO–CuO nanocomposites show a maximum specific capacitance of 800 F/g at 1 A/g. The nanocomposites showed enhanced electrochemical behaviour of the nanocomposites when compared to pure GO. The nanocomposites also showed good cycling stability. The superior performance of the GO–CuO and GO–ZnO nanocomposite electrode renders it as a promising material for supercapacitors applications.

Effect of low-temperature underwater plasma produced of new properties of Mo–Ti mixed oxide composites for electron transport layer in the dye-sensitized solar cells

TiO2-based composites are potential materials for dye solar cells. Here we report a new method for synthesizing a new composite material based on molybdenum and titanium oxides. Low-temperature underwater direct current plasma is used as a synthesis method, and Mo and Ti wires were as electrodes. The polarity of the electrode affects the nature of the array. It was found that with the positive polarity of the molybdenum electrode (anode), MoO3 decorated with rutile is formed. The mixed-phase TiO2 decorated MoOx (x = 2.75–2.85) is formed by the negative polarity Mo of the electrode (cathode). The synthesized composites show improved characteristics in the photocurrent response and photovoltaics.

The role of ZnO in the catalytic behaviour of Zn-Al mixed oxides in aldol condensation of furfural with acetone

The manuscript describes the key aspects of Zn-Al mixed oxides prepared by different methods (the so-called urea method and co-precipitation methods using either NaOH/Na2CO3 alkaline solution or solution of NaOH) affording high conversion and selectivity values in aldol condensation of furfural with acetone. The structure, composition and acid-base properties of Zn-Al mixed oxides were described by using of TGA, XRD, N2-adsorption, TPD-NH3/CO2 and in-situ diffuse reflectance spectroscopy and correlated with the catalytic performance of a series of Zn-Al mixed-oxides catalysts. Along with the impact of specific surface area and basicity on the furfural conversion, the conversion of furfural also increased with the increasing value of the edge of UV-vis spectrum of Zn-Al mixed oxide reflecting ZnO-Al2O3 interaction. We have introduced a simple method based on diffuse reflectance spectroscopy with a potential to predict furfural conversion over Zn-Al mixed oxides in aldol condensation of furfural with acetone.

Adsorption of acid orange 7 using green synthesized CaO/CeO2 composite: An insight into kinetics, equilibrium, thermodynamics, mass transfer and statistical models

The present research reported the co-precipitation mediated synthesis of mixed metallic oxide composite, CaO/CeO2 using ultrasound-assisted extract of Eichhornia crassipes leaves. Fourier Transform Infrared Spectroscopy (FT-IR), Thermo-gravimetric/Differential Thermal analysis (TG/DTA), X-ray Diffraction (XRD), and Brunauer-Emmet-Tellet (BET) isotherms ensured the formation of the mixed oxide. Further, the CaO/CeO2 composite was tested in the anionic azo dye, Acid Orange 7 (AO7) removal process. The optimal removal of 92.68% was attained in the initial solution pH of 2.0 with the composite dosage of 0.1 g for 10 mg/L of AO7 concentration, operating at the temperature of 301 K. Response Surface Methodology (RSM) and Artificial Neural Network (ANN) techniques were employed to model the dye removal process. A second-order quadratic model from Box-Behnken Design (BBD) predicted and optimized the dye removal percentage with high degree of statistical accuracy (Fcal > Ftab at df=9; p < 0.0001). Likewise, a three-layered ANN model using the Levenberg–Marquardt backpropagation algorithm well predicted the dye adsorption process with the least root mean square error values (RMSE 0.3020). Further, the mean impact value (MIV) method identified pH0 as the most influential batch variable in the AO7 dye adsorption process.

Boosted up stability and activity of oxygen vacancy enriched RuO2/MoO3 mixed oxide composite for oxygen evolution reaction

Iridium free, acidic-stable, cost-effective, and efficient oxygen evolution reaction (OER) electrocatalyst is considered to be the bottleneck in the quest for sustainable energy production/storage devices. RuO2 has been proved as a highly active and standard OER electrocatalyst with poor stability. Herein, we are successfully providing the facile approach to synthesize the mixed oxide composite of RuO2 tailored with MoO3. Fifty percent reduction of noble metal contents, two times enhanced activity and excellent durability as compared to pure homemade and commercial RuO2 have been confirmed by numerous characterization techniques. Enhanced electrochemical performance of best mixed oxide composite is observed due to increasing number of oxygen vacancies, electronic distortion, lower oxidation state of noble metal, and reduced value of the Tafel slope. Furthermore, the best composite shows the 7-fold increase in electrochemical surface area, 3.2 times improvement in the bulk mass activity, and less value of overpotential.