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

Mesoporous Ce_xZr_1−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/Ce_xZr_1−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 Ce_xZr_1−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/Ce_xZr_1−xO₂ was investigated in detail. The 400 °C-calcined 8%CuO/Ce_0.8Zr_0.2O₂ catalyst exhibits the highest activity with the complete toluene conversion temperature of 275 °C at the condition of GHSH = 33,000 h⁻¹ and the toluene concentration of 4400 ppm. The interfacial interaction between CuO and the Ce_xZr_1−xO₂ support, highly dispersed CuO nanoparticles and the nature of the support contribute to the high catalytic activity of mesoporous CuO/Ce_xZr_1−xO₂ nanocatalysts.     

The dehydrogenation of ethylbenzene with CO2 over CexZr1 − xO2 solid solutions

With the purpose of changing the lattice structure of CeO₂ and improving the transmission capacity of lattice oxygen, Ce_xZr_1 − xO₂ solid solutions with different Zr proportions were synthesized using a hydrothermal method and applied in oxidative dehydrogenation of ethylbenzene to styrene with CO₂ at 550 °C. The Ce_0.5Zr_0.5O₂ showed the highest activity with an ethylbenzene conversion of 55% and styrene selectivity above 86%. Analytical characterization showed that the lattice oxygen mobile capacity of Ce_xZr_1 − xO₂ solid solutions was enhanced, corresponding to the order as Ce_0.3Zr_0.7O₂ > Ce_0.5Zr_0.5O₂ > Ce_0.7Zr_0.3O₂ > CeO₂. The oxygen storage/release capacity, higher surface area and pore distribution of Ce–Zr mixed oxides play important roles in the activity of ethylbenzene dehydrogenation to styrene with CO₂.     

Knoevenagel condensation reaction over acid–base bifunctional nanocrystalline CexZr1−xO2 solid solutions

Highly thermally stable three-dimensional spongelike mesoporous Ce_xZr_1?xO₂ solid solutions consisting of nanometer size particles with different Ce/Zr compositions were synthesized by a modified sol–gel procedure using a triethanolamine/water mixture as a solvent to be used in liquid Knoevenagel condensation reaction. These materials were investigated in detail by means of X-ray diffraction (XRD), Raman spectroscopy, chemical analysis, X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM), UV–Vis spectroscopy, Fourier transform infrared spectroscopy (FT-IR) and adsorption microcalorimetry. The XRD, HRTEM and XPS studies proved the presence of nanocrystalline Ce_xZr_1?xO₂ solid solutions. These solid solutions showed excellent chemoselectivity in the classical Knoevenagel reaction. The large pore sizes (around 10 nm) highlight the possibility of using Ce_xZr_1?xO₂ as a support material for versatile catalytic systems. The results obtained from NH₃ and SO₂ adsorption microcalorimetry experiments successfully demonstrated the incorporation of ZrO₂ into the CeO₂ lattice resulting in both acidic and basic surface sites in a mixed oxide matrix.     

Crystalline structure and electrical properties of YCoxMn1−xO3 solid solutions

Solid solutions corresponding to YCo_xMn_1−xO₃ system with x=0.2...0.7 have been studied. The powders were prepared by solid state reaction of corresponding oxides. Sintered bodies were obtained firing between 1250 and 1350 °C. The incorporation of 25 at.% of Co in the Yttrium manganite induced the appearance of a perovskite-type phase with orthorhombic symmetry and Space Group Pbnm. This feature was extended at least up to an amount of 70 at.% of Co. The increase of the Co content from 25 to 70 at.% led to a monotonic decrease of the orthorhombicity factor b/a. Electrical measurements have shown a semiconducting behaviour for all solid solutions with the perovskite-type structure. The room temperature conductivity increased with Co until the 33 at.% of Co, and then decreased. The 60/40 Co/Mn composition showed an increase of the electrical conductivity in comparison to the 50/50 composition and a corresponding decrease of the activation energy. Small polaron hopping mechanism is supposed to control the conductivity.     

Structure dependent catalytic activity of Ce0.8Tb0.2O2−δ and TiO2 supported Ce0.8Tb0.2O2−δ solid solutions for CO oxidation

A facile coprecipitation and deposition precipitation method were used for synthesis of nanosized Ce_0.8Tb_0.2O_2−δ (CT) and Ce_0.8Tb_0.2O_2−δ/TiO₂ (CTT) solid solutions, respectively. The synthesized materials were characterized by various state-of-the-art techniques and evaluated for CO oxidation activity. Formation of CT solid solution was confirmed by XRD and Raman, and nanocrystalline nature by TEM. Characterization results further suggested formation of a new pyrochlore phase between TiO₂ and TbO₂ at 1073 K, and the presence of Ce³⁺ associated with lattice defects in all samples. Catalytic results showed that CT calcined at 773 K exhibits a high activity and correlates well with physicochemical characteristics.     

Effect of Zr-doping on Pd/CexZr1−xO2 catalysts for oxidative carbonylation of phenol

Ce–Zr solid solution (Ce_xZr_1−xO₂, CZO) was prepared by the citric acid sol–gel method. The CZO was then used as a support for Pd/CZO catalysts for the oxidative carbonylation of phenol to diphenyl carbonate. The Pd/CZO catalyst showed enhanced activity and diphenyl carbonate selectivity compared with the Pd/CeO₂ catalyst. The catalytic performance of Pd/CZO was influenced by the calcination temperature of the CZO support. X-ray diffraction, scanning electron microscopy, N₂ adsorption–desorption measurements, X-ray photoelectron spectroscopy and H₂ temperature-programmed reduction measurements were used to investigate the effects of Zr doping and calcination temperature. The catalytic performance of Pd/CZO and Pd/CeO₂ for the oxidative carbonylation of phenol was affected by several factors, including the specific surface area, Ce³⁺ and/or oxygen vacancy content, oxygen species type and Pd(II) content of the catalyst. All these properties were influenced by Zr doping and the calcination temperature of the CZO support.     

Improved thermoelectric properties of layered Ti1−xNbxS2−ySey solid solutions

The thermoelectric properties of a series of the polycrystalline samples of titanium dichalcogenides with partial substitution of Ti for Nb and S for Se were investigated. It was found that sintering of the samples improved the thermoelectric efficiency (ZT), and the maximum ZT was achieved at sintering temperature of 600°C. A further increase in the sintering temperature (850°C and 950°C) led to the recrystallization of the samples, as a result, the Seebeck coefficient sharply decreased and electrical conductivity dramatically increased. The temperature dependences of electrical conductivity σ(T) in the temperature range from 4.2 to 300 K and Seebeck coefficient S(T) in the temperature range from 77 to 300 K were investigated in order to determine the nature of the observed improvements in thermoelectric properties due to double substitutions and sintering. Two-dimensionalization of electron transport properties of Ti_1−xNb_xS_2−ySe_y solid solutions was found. The Fermi energy E_F2D was estimated using the temperature dependences of Seebeck coefficient. The relationship between the Fermi energy E_F2D and figure of merit ZT was established. The effect of sintering on parameters σ(T), S(T), charge carrier concentration (n_2D), mobility (µ), and thermal conductivity (k) was found. The optimal value of Fermi energy E_F2D in terms of figure of merit ZT = 0.31 at room temperature (T = 300 K) was found for Ti_0.98Nb_0.02S_1.3Se_0.7 sample sintered at 600°C.     

The Effects of P-Poisoning of CexZr1−xO2 on the Transient Oxygen Storage and Release Kinetics

The present work reports on the investigation of the effects of chemical poisoning of Ce_xZr_1?xO₂ solids by phosphorous (P) on the kinetics of oxygen storage and release (OSR) of the thus derived P-contaminated solids, as a function of Ce_xZr_1?xO₂ solid composition (x = 0.3, 0.5 and 0.7) for the first time. Phosphorous deposition on the surface of Ce_xZr_1?xO₂ particles followed by calcination in air at 850 °C forms nano-crystals of CePO₄, which lead to a drastic decrease in the population of surface and subsurface reactive and mobile oxygen species due to the formation of P–O–Ce bonding. The concentration (μmol/g) of exchangeable ¹⁶O in the solid with ¹⁸O from the gas phase was found to increase, and the degree of reduction in the Oxygen Storage Capacity (OSC) to decrease with increasing Ce content in the Ce_xZr_1?xO₂ solid after P-poisoning. The increase in the Ce content of Ce_xZr_1?xO₂ makes its OSR properties more resistant against P-poisoning due to the increasing number of poison-free Ce atoms, which are able to participate in the Ce³⁺ ? Ce⁴⁺ redox cycle.     

Fractional-hydrolysis-driven formation of non-uniform dopant concentration catalyst nanoparticles of Ni/CexZr1 − xO2 and its catalysis in methanation of CO2

Ni/ceria–zirconia solid solution (Ni/Ce_xZr_1 − xO₂) with Ce and Ni enriched on the surface of the catalysts are prepared via a simple, low-cost method. The aqueous phase reactions simplify the preparation process, save the cost and lead the Ce to enriching on the surface of products. The impregnation method makes the Ni enriching on the surface of products which enhances the efficiency of active component. These catalysts exhibit significantly high catalytic performance. The formation mechanism is also investigated.     

Electrophysical properties of perovskite solid solutions in the system CaTiO3−La2O3

The electrophysical properties of perovskite solid solutions in the system CaTiO₃−La₂O₃ were investigated in the La₂O₃ concentration range of 0–40%. The composition dependences of permittivity, loss tangent, volume resistivity, and temperature coefficient of capacitance were plotted. The perovskite solid solutions under study hold special promise as raw materials for radioceramics. Translated from Ogneupory i Tekhnicheskaya Keramika, No. 1, pp. 11–13, January, 1998.     

High-temperature mechanical and thermal properties of Ca1−xSrxZrO3 solid solutions

Perovskite oxides are promising thermal barrier coatings (TBCs) materials but their thermophysical properties still need to be further improved before commercial applications. In this work, mechanical/thermal properties of calcium-strontium zirconate solid solutions (Ca_1−xSr_xZrO₃) are investigated. Comparing to the end-compounds CaZrO₃ and SrZrO₃, the solid solutions achieve the enhanced thermal expansion coefficient, decreased thermal conductivity as well as good high-temperature mechanical properties. The experimental thermal conductivities of Ca_1−xSr_xZrO₃ (x = 0.2, 0.4, 0.6, 0.8) are in the range of 1.76-1.94 W·(m·K)⁻¹ at 1073 K, being lower than that of the yttria-stabilized zirconia (YSZ). At the same time, their thermal expansion coefficients (10.75 × 10⁻⁶-11.23 × 10⁻⁶/K at 1473 K) are comparable to that of YSZ. Moreover, the Young's moduli of Ca_0.8Sr_0.2ZrO₃, Ca_0.6Sr_0.4ZrO₃, Ca_0.4Sr_0.6ZrO₃, and Ca_0.2Sr_0.8ZrO₃ at 1473 K are 70.7%, 69.4%, 68.8%, and 71.1% of the corresponding values at room temperature, respectively. The good high-temperature mechanical and thermal properties ensure the potential applications of Ca_1−xSr_xZrO₃ solid solutions as high-temperature thermal insulation materials including TBCs.     

The catalytic activity of the Pr2Zr2−xFexO7±δ system for the CO oxidation reaction

One of the alternatives to decrease the concentration of CO is its oxidation reaction to CO₂, which can be made more efficient using catalysts. In this work, it is shown that pyrochlore structures are a promising candidate to act as heterogeneous catalysts due to their chemical and physical properties. For use as a catalyst in this reaction, the Pr₂Zr_2−xFe_xO_7±δ (x = 0, 0.05, 0.10, and 0.15) system was synthesized by the solvothermal method, firing the powder obtained at temperatures of 1200 and 1400°C. The diffraction patterns confirmed the pyrochlore structure as the single phase in all the nominal compositions. The Brunauer–Emmett–Teller method and dynamic light-scattering analysis showed an increase in the particle size and a decrease in the specific surface area when increasing the iron concentration and increasing the calcination temperature. The compositions that presented the best catalytic activity were the samples with the highest iron concentration. Moreover, these samples were able to convert all the CO oxidation reactions in a narrower temperature range than a conventional CeO₂ sample. The presence of vacancies and the redox behavior of the elements present are the key factors for the catalysis of this system in the CO oxidation reaction.     

Preparation of CuxCe1?xO2?x/SBA-15 catalysts and the catalytic properties of CO oxidation

Cu_xCe_1?xO_2?x/SBA-15 (x?=?0?C1) catalysts were prepared using the mesoporous silica material SBA-15 as the support. The catalysts were characterized by N₂ adsorption?Cdesorption, X-ray diffraction, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy and temperature-programmed reduction. The catalytic activity of the catalysts for the oxidation of CO was evaluated and the activation energies were obtained by avoiding internal and external diffusions. The results indicated that highly dispersed CuO was formed in the obtained catalysts when the Cu content was low. Co-impregnation with Cu and Ce salt solutions does not destroy the SBA-15 mesoporous structure. Both Cu²⁺ and Cu⁺ existed on the surface of the obtained catalysts, while the Ce⁴⁺ was the main Ce species. All the obtained catalysts showed excellent activities for the combustion of CO. CO could be totally oxidized at 187?°C at the space velocity of 48,000?mL/(g?h).     

Investigation of the Intrinsic Activity of ZrxCe1−xO2 Mixed Oxides in the CO + NO Reactions: Influence of Pd Incorporation

The intrinsic activity of various Zr _x Ce_1–x O₂ mixed oxides and after a Pd deposition has been investigated in the CO + NO reactions from temperature-programmed experiments performed under stoichiometric conditions. It has been found that the activity of Zr _x Ce_1–x O₂ depends on either the specific surface area or the number of Ce cations and their intrinsic activity, Zr_0.5Ce_0.5O₂ being the most active support. The addition of palladium strongly enhances the catalytic activity of the supports probably due to a synergistic effect between CeO₂ and the metal since the initial activity of palladium-based catalysts is directly related to their Ce content. Such a catalytic enhancement has been explained by a bifunctional mechanism involving active sites probably composed of Pd and ceria. A strong deactivation operates leading to the disappearance of the beneficial effect of ceria. Such a deactivation seems to be dependent on the support composition, Pd supported Zr_0.25Ce_0.75O₂ being the most resistant to deactivation.     

New solid solutions of mixed alkali-zinc diphosphates LiNa1 − x K x ZnP2O7

Phase relationships in the LiNaZnP₂O₇-LiKZnP₂O₇ system have been studied. For the first time a vast region of solid solutions of the rhombic syngony LiNa_{1 ? x} K _x ZnP₂O₇ containing simultaneously three alkali cations was found. The miscibility is broken at the temperature of the polymorphous transformations LiKZnP₂O₇ (270°C) and below, with the formation of the two-phase region of the solid solution with the rhombic and monoclinic structures (0.85 ≤ x ≤ 1 at 25°C).     

Spinel precipitation in Sn4+-doped Co1−xO polycrystals with dispersed Co2+xSn1−xO4 particles

Co_1?xO–SnO₂ powders in molar ratio of 92:8 were reactively sintered at 1400 °C to form Co_1?xO–Co_2+xSn_1?xO₄ composite and then cooled in furnace or air quenched for secondary Co_2+xSn_1?xO₄ spinel precipitation from the Sn⁴⁺ doped Co_1?xO grains. Electron microscope observations indicated the secondary spinel to precipitate at grain boundaries when slowly cooled, but as parallel-epitaxial platelets within the Sn⁴⁺ doped Co_1?xO grains with a precipitate free zone near the grain boundary when air quenched. A process of thermal-mismatch induced {1 1 0} cleaving, taking advantage of cobalt vacancies, and spontaneous healing by oxidation precipitation accounts for the platy spinel precipitation within the grains. The precipitate free zone can be attributed to cobalt vacancy depletion, i.e. site saturation, near the grain boundary during rapid cooling in air. The spinel nanocrystals nucleated from cobalt vacancies in association with Sn⁴⁺ dopant have well-developed {1 1 1} habit plane in order to minimize the coherency strain energy.     

Composition-dependent microstructure and electrical property of (1−x)SBN-xBNBT solid solutions

In this study, (1−x)Sr_0.75Ba_0.25Nb₂O₆-x[0.94Bi_0.5Na_0.5TiO₃-0.06BaTiO₃] solid solution ceramics were prepared and investigated. The length-diameter ratio of pillar-like grain increased with increase in x, reaching maximum value of 10.5 at average length of 1.36 μm and diameter of 0.13 μm for x = 0.20. The maximum dielectric constant, temperature corresponding to the maximum dielectric constant, and saturated polarization decreased, respectively, from 507, 36°C, and 3.2 μC/cm² for x = 0 to 365, −61°C, and 2.0 μC/cm² fort x = 0.10, and then increased to 1167, 43°C, and 5.5 μC/cm² for x = 0.20. These results indicate the competitive effects of B-site Ti⁴⁺ and A-site Ba²⁺ on ferroelectricity.     

Catalytic properties of SrSn1−xSbxO3 in methanol oxidation

Ceramic model catalyst materials of general formula SrSn_1–x Sb _x O₃ are synthesised by solid state reaction. X-ray diffraction shows the materials to be single phase over the composition range 0 x0.085, with a second phase, identified as SrSb₂O₅, being produced at higher antimony doping levels. XPS, Auger electron spectroscopy and valence band photoemission show strong segregation of Sb to the surface of the material even within the single phase regime. The catalytic properties of the materials are examined using methanol oxidation as a test reaction. The activity and selectivity to formaldehyde production shown by these materials is found to be strongly correlated with the attainment of the bulk solubility limit of Sb in the SrSnO₃ perovskite host.     

Mesoporous CuO/TixZr1 − xO2 catalysts for low-temperature CO oxidation

Mesoporous CuO/Ti_xZr_1 − xO₂ catalysts were prepared by a surfactant-assisted method, and characterized by N₂ adsorption/desorption, TEM, XPS, in-situ FTIR and H₂-TPR. The catalysts exhibited high specific surface area (S_BET = 241 m²/g) and uniform pore size distribution. XPS and in-situ FTIR displayed that Cu⁺ and Cu²⁺ species coexisted in the catalysts. The CuO/Ti_xZr_1 − xO₂ catalysts presented obviously higher activity in CO oxidation reaction than the CuO/TiO₂ and CuO/ZrO₂ catalysts. Effect of molar ratios of Ti to Zr and calcination temperature on catalytic activity was investigated. The CuO/Ti_0.6Zr_0.4O₂ catalyst calcined at 400 °C exhibited excellent activity with 100% CO conversion at 140 °C.