xO2 Solid Solutions Research Articles

Effect of CeO$lt;inf$gt;2$lt;/inf$gt;-based Solid Solutions on Hydrogen Storage Kinetic Properties of Mg$lt;inf$gt;2$lt;/inf$gt;Ni Alloy

Nanosized Ce1-x(Eu0.5La0.5)xO2 and Ce1-x(Fe0.5La0.5)xO2 solid solutions were synthesized via hydrothermal method, and the doping effect was characterized by analyzing the structure and spectrum features of the solid solu- tions. The results showed that the cell parameters of the solid solutions increased, the absorption edge of the UV diffuse reflectance spectroscopy was drifted, and the characteristic Raman F2g vibration peak shifted to lower wave numbers. Then the mixtures of Mg2Ni alloy powders and the solid solution additives were ball-milled to obtain composites. XRD results showed that the fraction of amorphous and nanocrystalline in the as-prepared composites was increased. The hydrogen storage kinetic measurements demonstrated that surface activity and degree of re- versibility of the composites was optimized, and the diffusion rate and diffusion coefficient of hydrogen atoms in the bulk of Mg2Ni were increased.

Order parameter and scaling behavior in BaZrxTi1−xO3 (0.3 < x < 0.6) relaxor ferroelectrics

We report the relaxor behavior of the zirconium doped barium titanate BaZrxTi1−xO3 solid solutions and discuss the temperature, frequency, and concentration dependence in terms of correlations among the polar nanoregions. The relaxor behavior is analyzed within the mean field theory by estimating the Edward-Anderson order parameter qEA. Additionally, we find that qEA calculated for the different concentrations obeys a scaling behavior qEA=1−(T/Tm)n, where Tm are the respective dielectric maxima temperatures and n = 2.0 ± 0.1. The frequency dependence of the qEA also shows results consistent with the above mentioned picture.

(Ti,Sn) solid solutions as functional materials for gas sensing

Metal-oxide semiconductors are widely used as functional materials for gas sensing because of their chemoresistive effect when interacting with ambient gases. For this work, nanosized TixSn1−xO2 have been synthesized at increasing Ti molar ratio (x=0, 0.1, 0.2, 0.25, 0.3, 0.5, 0.7, 0.8, 0.9, 0.95, 1) and extensively investigated through a wide variety of characterizations. It turned out that the merging process of the two single oxides formed new compounds with improved gas responses compared to pure TiO2 and also to pure SnO2. Moreover, all investigated physico-chemical characteristics resulted tuneable through the titanium content in the solid solution. Each characterization carried out onto TixSn1−xO2 solid solutions made it possible to identify two classes of materials with SnO2-like or TiO2-like behaviours, the best CO response being on the intersection of the two species of materials. Moreover, a very interesting analysis on the generally accepted electrical transport model through polycrystalline semiconductors has been carried out. Indeed, the comparison with experimental evidences has highlighted a conduction mechanism not previously considered.

Mesoporous CexZr1−xO2 solid solutions supported CuO nanocatalysts for toluene total oxidation

Mesoporous CexZr1−xO2 solid solutions were prepared by the surfactant-assisted method and used as support of CuO nanocatalysts for catalytic total oxidation of toluene. The prepared CuO/CexZr1−xO2 catalysts have a wormhole-like mesoporous structure with high surface area and uniform pore size distribution, and the CuO nanoparticles were highly dispersed on the surface of CexZr1−xO2. The doping of ZrO2 in CeO2 promotes the dispersion of active copper species and enhances the reducibility of copper species. The effect of Ce/Zr ratio, calcination temperature and CuO loading amount on the catalytic performance of CuO/CexZr1−xO2 was investigated in detail. The 400°C-calcined 8%CuO/Ce0.8Zr0.2O2 catalyst exhibits the highest activity with the complete toluene conversion temperature of 275°C at the condition of GHSH=33,000h−1 and the toluene concentration of 4400ppm. The interfacial interaction between CuO and the CexZr1−xO2 support, highly dispersed CuO nanoparticles and the nature of the support contribute to the high catalytic activity of mesoporous CuO/CexZr1−xO2 nanocatalysts.

Catalytic Wet Peroxide Oxidation of Chlorophenol Over a Ce0.86Cu0.14–x O2 Catalyst

Abstract A Ce0.86Cu0.14–x O2 catalyst was prepared by the citric acid complex method and characterized by X-ray diffraction, scanning electron microscopy, and temperature-programmed reduction, and its activity in the catalytic wet peroxide oxidation of 4-chlorophenol (4-CP) and 2,4-dichlorophenol (2,4-DCP) was investigated. The results showed that the Cu2+ ions dissolved into the CeO2 lattice to form a Ce0.86Cu0.14–x O2 solid solution with a coarse, interconnected, porous, and cotton-like morphology. The metal–oxygen bonds were weakened by solid-solution formation in the Ce0.86Cu0.14–x O2 catalyst. This weakening facilitated H2O2 activation and decomposition to form highly oxidative HO∙ species that can lead to significant chlorophenol mineralization. A total organic carbon removal rate greater than 80% was achieved after 2 h reaction at 50°C and at an initial 4-CP and 2,4-DCP concentration of 50 mg/L. The effects of H2O2 dosage, catalyst dosage, and initial chlorophenol concentration on catalytic efficiency were also determined.

Influence of B-site complex-ion substitution on the structure and electrical properties in Bi0.5Na0.5TiO3-based lead-free solid solutions

The influence of B-site complex-ion substitution on the phase transition and dielectric, ferroelectric, piezoelectric properties in (Bi0.5Na0.5)0.93Ba0.07Ti1−x(Al0.5Nb0.5)xO3 solid solutions was investigated in detail and a schematic phase diagram was established. The substitution was found to induce a phase transition from the ferroelectric long range order to relaxor pseudocubic phase. A maximum quasi-static piezoelectric coefficient d33 of 210 pC/N was obtained. Furthermore, at a critical composition x of 0.02, large strain response of ∼0.29% was obtained under ∼5 kV/mm at room temperature with the normalized strain Smax/Emax as high as 575 pm/V. The high strain behavior was attributed to the field-induced phase transition from ergodic relaxor pseudocubic to ferroelectric phases. The large strain response with good temperature stability would be quite suitable for environmental-friendly solid-state actuator applications.

Effect of steam content and O2 pretreatment on the catalytic activities of Au/CeO2–Fe2O3 catalysts for steam reforming of methanol

The Au/CeO2–Fe2O3 prepared by deposition–precipitation were studied by steam reforming of methanol at a reaction temperature range of 200–400°C. Complete methanol conversion was obtained at the optimal steam/methanol ratio of 2 at 400°C. A high steam content strongly depressed both methanol conversion and hydrogen concentration since this led to a complex mechanism and the formation of carbonate and formate species. After pretreating with oxygen, the catalytic activity dramatically decreased with the presence of an inhomogeneous CexFe1−xO2 solid solution phase; the covering Au sites by the free α-Fe2O3 particles; and an agglomeration of both free α-Fe2O3 and Au particles.

Co/CexZr1−xO2 solid-solution catalysts with cubic fluorite structure for carbon dioxide reforming of methane

The Co/CexZr1−xO2 catalysts were prepared by the impregnation method and characterized via BET, NH3-TPD, XRD, H2-TPD, H2-TPR, TEM and TG–DSC techniques. The study showed that the Co3O4 crystallites had better dispersion on the cubic fluorite CexZr1−xO2 supports compared with on the ZrO2 and CeO2, and the Co/Ce0.6Zr0.4O2 retained the cubic fluorite structure after the reaction. The Ce0.6Zr0.4O2 catalyst showed good catalytic performance, which was attributed to the alkalescence of support surface, better dispersion of active species, better textural property and reducibility. The deposition carbon over the Co/Ce0.6Zr0.4O2 catalyst mainly existed in the form of low-temperature carbon.

Dry reforming of methane to synthesis gas on NiO–MgO nanocrystalline solid solution catalysts

The catalytic performance of nickel–magnesia catalysts in CO2 reforming of methane and the factors influencing carbon deposition during the reaction were investigated by a comparative study of different reduced NixMg1−xO solid solution catalysts. With the characterization results of X-ray diffraction (XRD), BET surface area, scanning electron microscopy (SEM) and thermal gravimetric analysis (TGA) it was found that the excellent anti-coking performance of reduced solid solution catalyst with low Ni content is attributable to high dispersion of reduced Ni species, basicity of support surface and nickel–support interaction.

Low temperature hydrogen production by catalytic steam reforming of methane in an electric field

Catalytic steam reforming of methane in an electric field (electroreforming) at low temperatures such as 423 K was investigated. Pt catalysts supported on CeO2, CexZr1−xO2 solid solution and a physical mixture of CeO2 and other insulators (ZrO2, Al2O3 or SiO2) were used for electroreforming. Among these catalysts, Pt catalyst supported on CexZr1−xO2 solid solution showed the highest activity for electroreforming (CH4 conv. = 40.6% at 535.1 K). Results show that the interaction among the electrons, metal loading, and catalyst support was important for high catalytic activity on the electroreforming. Catalytic activity of the electroreforming increased in direct relation to the input current. Characterizations using X-ray diffraction (XRD), temperature programmed reduction with H2 (H2-TPR), and alternate current (AC) impedance measurement show that the catalyst structure is an important factor for activity of electroreforming.

Crystal structure and ferroelectric properties of Bi<sub>0.5</sub>Na<sub>0.5</sub>TiO<sub>3</sub>-modified Bi<sub>0.5+0.5</sub><i><sub>x</sub></i>Na<sub>0.5−0.5</sub><i><sub>x</sub></i>Ti<sub>1−</sub><i><sub>x</sub></i>Mn<sub>0.75</sub><i><sub>x</sub></i>Mo<sub>0.25</sub><i><sub>x</sub></i>O<sub>3</sub> solid solutions

Crystal structure and ferroelectric properties of Bi<sub>0.5</sub>Na<sub>0.5</sub>TiO<sub>3</sub>-modified Bi<sub>0.5+0.5</sub><i><sub>x</sub></i>Na<sub>0.5−0.5</sub><i><sub>x</sub></i>Ti<sub>1−</sub><i><sub>x</sub></i>Mn<sub>0.75</sub><i><sub>x</sub></i>Mo<sub>0.25</sub><i><sub>x</sub></i>O<sub>3</sub> solid solutions

One-pot hydrothermal synthesis and high temperature thermal stability of CexZr1−xO2 nanocrystals

We report a facile one–pot synthesis of CexZr1−xO2 (0 ≤ x ≤ 1) solid solution nanocrystals using hydrothermal reactions. A direct formation of oxide solid solutions in aqueous solution under pressure at low temperatures was clearly revealed by X-ray diffraction, Raman spectroscopy, and chemical composition analysis of individual nanocrystals using energy dispersive X-ray spectroscopy in scanning transmission electron microscopy mode. Chemisorption behavior of the synthesized nanocrystals was characterized using a hydrogen temperature programmed reduction, which showed a superior low-temperature activity in CexZr1−xO2 (0 < x < 1) compared to pure CeO2. Furthermore, we investigated the thermal stability of the prepared Ce0.5Zr0.5O2 at high temperatures (900 °C–1400 °C) under oxidation and reduction atmosphere. The effect of varying conditions of heat-treatment has given information on the phase transformation in Ce0.5Zr0.5O2 from pseudocubic to tetragonal structure under oxidation atmosphere, and to pyrochlore structure under reduction atmosphere.

Influence of cobalt content on the electrochemical properties of sheet-like 0.5Li2MnO3·0.5LiNi1/3+xCo1/3−2xMn1/3+xO2 as lithium ion battery cathodes

The promising cathode materials of serial 0.5Li2MnO3·0.5LiNi1/3+xCo1/3−2xMn1/3+xO2 (x = 1/12, 1/24, 0, −1/24 and −1/12) solid solutions have been synthesized by a polymerization–pyrolysis-assisted crystallization route. X-Ray diffraction (XRD) and scanning electron microscope (SEM) characterization show that all the powdered solid solutions possess a two-dimensional sheet-like superstructure composed of crystalline nanoparticles. Galvanostatic charging–discharging tests exhibit that, as high-capacity cathodes, the initial coulombic efficiency and cycling stability of these sheet-like configurations depend upon the cobalt content (i.e., the value of (1/3 − 2x) difference) in chemical formula 0.5Li2MnO3·0.5LiNi1/3+xCo1/3−2xMn1/3+xO2, giving an optimal x value in the range of 0 and 1/12. Considering the initial activation of component Li2MnO3 and the unwanted phase change of Co-contained component LiNi1/3+xCo1/3−2xMn1/3+xO2 at a charging voltage higher than 4.55 V, the cyclability and electrode polarization of serial sheets have also been estimated within a narrow electrochemical window of 2.0 and 4.3 V. To compare with the electrochemical parameters of serial solid solutions obtained within 2.0 and 4.7 V, therein an extremely high capacity retention ratio of 99.2% (x = 1/12) or 95.4% (x = 0) is observed at 0.5 C over 50 charge–discharge cycles.

Thermodynamic properties of CexTh1−xO2 solid solution from first-principles calculations

A systematic study based on first-principles calculations along with a quasi-harmonic approximation has been conducted to calculate the thermodynamic properties of the CexTh1−xO2 solid solution. The predicted density, thermal expansion coefficients, heat capacity and thermal conductivity for the CexTh1−xO2 solid solution all agree well with the available experimental data. The thermal expansion coefficient for ThO2 increases with CeO2 substitution, and complete substitution shows the highest expansion coefficient. On the other hand, the mixed CexTh1−xO2 (0<x<1) solid solution generally exhibits lower heat capacity and thermal conductivity than the ThO2 and CeO2 end members. Our calculations indicate a strong effect of Ce concentration on the thermodynamic properties of the CexTh1−xO2 solid solution.

Vacancy-Driven Surface Segregation in Ni x Mg1−x O(100) Solid Solutions from First Principles Calculations

Reduced Ni x Mg1−x O solid solutions are promising catalytic materials for the dry reforming of methane with carbon dioxide, a reaction of tremendous importance that converts two green-house gases into syn-gas. Conventional nickel-based catalysts have been found to encounter carbon deposition (i.e., coking), one of the major resources that cause the catalyst deactivation. Previous studies suggested that MgO-supported Ni nanoparticles produced from the reduction of Ni x Mg1−x O can inhibit the accumulation of carbon. The efficiency and durability of the catalyst strongly depends on the morphology. Here we employed density functional theory to investigate the structural changes of the Ni x Mg1−x O(100) solid solution under different conditions. Our results show that Ni ions preferentially anti-segregate to the subsurface layers of the MgO matrix during the NiO–MgO intermixing. Under reducing conditions, Ni ions facilitates the generation of oxygen vacancies, which prefer to couple together with Ni ions inside the MgO matrix to form a Ni ion–oxygen vacancy pair. In addition, the segregation of a Ni ion–oxygen vacancy pair can be controlled by changing the concentrations of Ni ions. This is driven by the strong interaction between oxygen vacancies and Ni ions. It is well known that oxygen vacancies play an important role during a catalytic reaction on an oxide, providing active sites to help the adsorption and dissociation of reaction intermediates. Our results show that in mixed oxides oxygen vacancies could also drive the segregation of the catalytically active components and provide new opportunities to tune the catalytic activity of oxides.

Enhancement in CO oxidation activity of nanosized CexZr1−xO2 solid solutions by incorporation of additional dopants

The influence of Hf, Pr and Tb dopant cations on structural and catalytic properties of nanosized CexZr1−xO2 solid solutions has been investigated. A wide range of analytical techniques are utilized to characterize the synthesized materials, and the catalytic activity is evaluated for CO oxidation. XRD, Raman, SEM and TEM results suggested formation of dopant cation incorporated ceria–zirconia solid solutions with highly homogeneous morphology and lattice defects. The CO-TPR measurements revealed an enhanced reducibility of CexZr1−xO2 which is reflected in their better catalytic activity. The role of Tb4+/Tb3+ and Pr4+/Pr3+ redox couples in facilitating a higher activity has been addressed.

MnxCo3−xO4 solid solution as high-efficient catalysts for low-temperature oxidation of formaldehyde

Abstract Mn x Co 3 − x O 4 solid solution was synthesized by co-precipitation method and tested for the first time for oxidation of HCHO. The formation of Mn x Co 3 − x O 4 solid solution was confirmed by XRD, H 2 -TPR, XPS studies. It was observed that complete conversion of HCHO occurred at 75 °C (GHSV = 60,000 h − 1 , relative humidity = 50% (25 °C)), and remained unchanged within 50 h. Such high activity can be ascribed to the large amount of surface oxygen available on Mn x Co 3 − x O 4 . According to the results of in situ DRIFTs, we proposed a reaction pathway for HCHO oxidation over Mn x Co 3 − x O 4 catalyst.

Thermodynamics of Nanocrystalline Sn0.586Ti0.414O2 Rutile Solid Solution: Comparison with Nanocrystalline SnO2 and TiO2 and with Bulk Materials

Nanocrystalline Sn x Ti 1−x O 2 rutile solid solutions are important materials for a variety of gas sensors and catalysts. Although thermodynamic data are available for nanocrystalline SnO 2 and TiO 2 and for bulk (coarse‐grained) Sn x Ti 1−x O 2 solid solutions, there is a lack of experimental thermochemical data on the energetics of Sn x Ti 1−x O 2 nanoparticles. In this work, Sn 0.586 Ti 0.414 O 2 rutile solid solution nanoparticles were synthesized. The surface energies of anhydrous and hydrated nanoparticles were measured by combining high‐temperature oxide melt solution calorimetry molten 2PbO·B2O3 at 800°C and water adsorption calorimetry. The surface energy of the anhydrous surface is 2.02 ± 0.03 J·m−2, and that of the hydrated surface is 1.68 ± 0.03 J·m−2. These values lie between the previously reported surface energies of rutile SnO2 and TiO2. The integral heat of water adsorption is −80 kJ·mol−1, with a chemisorbed maximum coverage of ~6 H2O·nm−2. These values are also between those for TiO2 and SnO2 (rutile) reported previously. The strongly positive (unfavorable) energetics of mixing in SnO2–TiO2 bulk solid solutions are predicted to change little at the nanoscale, and the extensive solid solution seen in the nanophase system prepared near room temperature reflects kinetic hindrance to exsolution of an initially homogeneous precipitate rather than thermodynamic stability.

High-field dielectric properties and Raman spectroscopic investigation of the ferroelectric-to-relaxor crossover in BaSnxTi1−xO3 ceramics

BaSnxTi1−xO3 solid solutions with compositions in the range x = 0–0.20 were studied by combining analysis of the field-induced dielectric and ferroelectric properties with Raman spectroscopic investigations. By combining techniques, the detection of specific features related to the ferroelectric-to-relaxor crossover with increasing Sn content is possible. Detailed tunability analysis of the x = 0.05 composition indicated that multiple components contribute to the dc-field induced permittivity response; these components are active in different temperature and field ranges and could be assigned to a few polarization mechanisms. First order reversal curves (FORC) for the material clearly show a transition from ferroelectric-to-relaxor behavior with increasing x, confirming the conclusions from the Raman and dielectric studies. This was evidenced by the shift of the FORC distribution over coercivities toward zero field values. Raman measurements allow the identification of the separate phases with varying Sn content and temperature, indicating large regions of phase coexistence. The composition x = 0.20 is in a predominantly relaxor state. This is ascribed to a large range of phase coexistence and to the presence of polar nanoregions promoted by Sn substitution on the B site of the perovskite unit cell ABO3.

TixSn1−xO3 solid solution as an anode material in lithium-ion batteries

TixSn1−xO3 solid solutions were prepared by a hydrothermal process. The morphologies and structures of TixSn1−xO3 solid solutions were investigated by scanning electron microscope, transmission electron microscope and X-ray diffraction measurements. The electrochemical properties of TixSn1−xO3 solid solution electrodes with different Sn/Ti ratios were examined by a variety of electrochemical testing methods. It was found that, the TixSn1−xO3 solid solution showed not only higher specific capacity of 506mAhg−1 after 30 cycles but also better cycle performance, superior than the pure SnO2 electrode, which can be ascribed to the stable cyclability of TiO2 and the high reversible capacity of nanosized SnO2. The TixSn1−xO3 solid solutions would be a potential candidate as anode material for a new generation lithium ion batteries.