Beneficial effect of adding γ-AlOOH to the γ-Al2O3 washcoat of a PdO catalyst for methane oxidation

The beneficial effect of adding γ-AlOOH to the γ-Al₂O₃ washcoat of a ceramic cordierite (2MgO · 2Al₂O₃ · 5SiO₂) monolith, used to support a PdO catalyst, is reported for methane oxidation in the presence of water at low temperature (<500°C). The mini-monolith (400 cells per square inch (CPI), 1 cm diameter × 2.54 cm length; ~52 cells) was washcoated using a suspension of γ-Al₂O₃ plus boehmite (γ-AlOOH), followed by calcination and then deposition of Pd by wet impregnation. An optimum solid content of 25 wt% in the washcoat suspension was used to obtain a ~25 wt% washcoat on the monolith. The presence of γ-AlOOH enhanced the thermal and mechanical stability of the washcoat, provided that the γ-AlOOH content was <8 wt%. Temperature-programmed methane oxidation (TPO) showed that the addition of γ-AlOOH to the γ-Al₂O₃ washcoat decreased the catalyst activity. However, when H₂O (2 vol% and 5 vol%) was present in the feed gas, the γ-AlOOH improved the catalyst activity and stability. A γ-AlOOH content of ~5 wt% in the washcoat was determined to provide the highest catalyst activity and stability for CH₄ oxidation in the presence of water.     

Characterization of a soldering system consisting of a glass from the system CaOAl2O3B2O3SiO2 and wollastonite

In this work, the characterization of a soldering system with wollastonite as filler added as powder to the powdered base glass is shown. A soldering system consisting of the base glass and a coexisting crystalline phase is created which is then pressed to pellets and sintered to maximum density.Wollastonite increases the thermal expansion coefficient of the base glass after sintering the samples. In the present paper, the sintering behavior of the soldering system and possible interactions between glass and filler are analyzed. Also, density and porosity after sintering and the resulting crystalline phases are characterized.The mixtures with wollastonite contents up to 30% showed suitable sintering behavior and good density (low porosity). From 40% wollastonite on, the sintering of the samples was not satisfying and porosity was still high after sintering. The main crystalline phases were anorthite, wollastonite and pseudowollastonite, which occurred in all samples. This shows that all three phases are coexisting phases of the glass composition.     

On the Possibility of Forming Complexes with the Participation of O2– Ions in Melts and Glasses of the Na2O–SiO2–Cu2O System

The structural role of copper ions in melts (glasses) of the Na₂O–SiO₂–Cu₂O–CuO system is analyzed in the framework of the acid–base concept with due regard for the geometric (the radius ratio for Cu²⁽¹⁾⁺ and O^2– ions) and energy (the mean enthalpies of the Cu²⁽¹⁾⁺–O bonds) factors. It is demonstrated that copper ions in the structure fulfill the function of modifier cations. In these melts, the Cu¹⁺–Cu²⁺ redox equilibrium can be described without regard for the formation of [Cu²⁽¹⁾⁺O_4/2]^2(3)– ionic complexes (which could be incorporated into the structure of silicon–oxygen anions) and [Cu²⁺O _b/k ]^{2 – b/k} polyhedra providing the interaction between Cu²⁺ ions and anions. The influence of the formation of these polyhedra on the redox equilibrium is considered within the formalism of chemical thermodynamics. The composition dependence of the oxygen ion exponent pO is measured by an electromotive force (emf) technique. The ratio between the numbers of copper atoms with different valences is determined by chemical analysis. The experimental data obtained are in agreement with the theoretical inferences.     

Effect of Tungsten Oxide on the Crystallization Properties of Glasses of the B2O3–La2O3–Nb2O5 System

Glass Physics and Chemistry - The effect of tungsten oxide on the crystallization properties of glasses of the 37.5B2O3 22.5La2O3 (40 – x)Nb2O5 xWO3 (where x = 10, 15, 20, 30, 40 mol %)...     

Promotional effect of H2O on the activity of In2O3‐doped Ga2O3–Al2O3 for the selective reduction of nitrogen monoxide

Effect of metal oxide additives on the catalytic performance of Ga₂O₃–Al₂O₃ prepared by the sol–gel method for the selective reduction of NO with propene in the presence of oxygen was studied. Of several metal oxide additives, the addition of In₂O₃ enhanced drastically the activity of Ga₂O₃–Al₂O₃ for NO reduction by propene in the presence of H₂O. In addition, the activity of In₂O₃‐doped Ga₂O₃–Al₂O₃ catalyst was extremely intensified by the presence of H₂O below 350°C. The promotional effect of H₂O was interpreted by the suppression of undesirable propene oxidation and the removal of carbonaceous materials deposited on the catalyst surface. We also found that close interaction of In₂O₃ and Ga₂O₃ is necessary for the enhancement of activity by H₂O. A lot of hydrocarbons except methane and oxygenated compounds served as good reducing agents, among which propene and 2‐propanol were the most efficient ones. In₂O₃‐doped Ga₂O₃–Al₂O₃ catalyst was capable of reducing NO into N₂ quite efficiently in the presence of H₂O at a very high space velocity. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effects of a low amount of C on the phase transformations in the AlN–Al2O3 pseudo-binary system

The effects of a low amount of C on the phase transformations in the AlN–Al₂O₃ pseudo-binary system are reported in samples having an AlN content in mol% ranging between 44 and about 0. Various complementary experimental techniques were used to determine the nature of the phase equilibria. Carbon is embedded in the components of three eutectics as a function of the average chemical composition of the sample in AlN. In two of them, a component belonging to the quaternary system Al–O–N–C and having a wide composition range was found. Its X-ray and neutron diffraction spectra are well refined with a hexagonal crystalline structure.     

Effect of Fluorine Ion on the Electrical Properties of Glasses in the Na2O–P2O5 System

The temperature–concentration dependence of the electrical conductivity of glasses in the NaPO₃–NaF system has been investigated. The regularities revealed are interpreted from the standpoint of the structural microinhomogeneity of glasses, which is due to the formation of polar structural units of the Na⁺[O^–POO_2/2], Na₂ ⁺[O^– ₂POO_1/2], Na⁺[F^–POO_2/2], and Na⁺F^– types. It is shown that the concentration dependence of the electrical conductivity is governed by the ratio between the concentrations of these structural units.     

A Study of the Acid–Base Properties of Melts in the Na2O–B2O3–SiO2System: I. Composition Joins with a Na2O Content of Less Than 20 mol %

Three composition joins in the Na₂O–B₂O₃–SiO₂system at constant Na₂O contents of 5, 10, and 15 mol % are studied by the high-temperature method of determining oxygen ion exponents pO for oxide melts. It is found that the basicity of melts increases in going from the binary sodium borate system to the sodium silicate system. The acid–base properties of ternary melts are simulated under the assumption that their basicity is determined by the interaction in pseudobinary systems. It is shown that the basicity of the studied melts is governed, to a large extent, by the formation of the Na₂O · B₂O₃· 2SiO₂ternary compound.     

Enhanced Activity of Spinel-type Ga2O3–Al2O3 Mixed Oxide for the Dehydrogenation of Propane in the Presence of CO2

Catalytic performance of a series of Ga₂O₃–Al₂O₃ mixed oxides prepared by alcoholic-coprecipitation method for the dehydrogenation of propane in the presence of CO₂ was investigated. It is shown that the combination of Ga and Al oxides greatly improved the performance of the Ga₂O₃-based materials for catalytic dehydrogenation of propane, with the highest performance attainable at a Ga₂O₃–Al₂O₃ catalyst with a 20 mol% aluminum content. While the same tendency was observed for the specific activity normalized by BET surface area, significantly enhanced stability was achieved for Ga₂O₃–Al₂O₃ with higher aluminum content. X-ray diffraction (XRD) revealed that a homogeneous spinel-type Ga₂O₃–Al₂O₃ solid solution is uniformly formed by substitution of Ga³⁺ for Al³⁺ in the Al₂O₃ lattice. The enhanced activity of Ga₂O₃–Al₂O₃ mixed oxides was accounted for by the abundance of surface weak acid sites due to the synergetic interaction between Ga₂O₃ and Al₂O₃ in the solid solution systems.     

Active Sites of a NiSO4/γ-Al2O3 Catalyst for the Oligomerization of Isobutene

Structural characterization, the mechanism of catalytic activity generation and the nature of active sites of a NiSO₄/γ-Al₂O₃ catalyst for isobutene oligomerization were studied by temperature programmed reduction (TPR), X-ray diffraction (XRD), diffuse reflectance infrared fourier transformed (DRIFTS) and X-ray photoelectron spectroscopy (XPS) techniques. The TPR measurements together with the XRD data indicated that calcination of the catalyst at 500 °C did not form either nickel oxide or nickel aluminate. The presence of only one type of surface nickel species formed by the incorporation of nickel ions into the surface vacant sites of γ-alumina lattice was indicated by XPS with Ar⁺ ions sputtering and TPR measurements. XPS analysis of the calcined catalyst suggested that the oxidation state of nickel ions in the calcined catalyst was (+2) and after calcination the nickel ions were coordinated to relatively more basic ligands. The surface acid centers of the catalyst were found to be only Lewis type. SO₄ ^2? ions were found to be present as a chelating bidentate ligand and enhanced the acidity of metal ( $ {\text{Al}}^{3 + } $ and/or $ {\text{Ni}}^{2 + } $ ) Lewis acid centers. The results suggested that the combined effects of the presence of the bidentate SO₄ ^2? ligand and dehydroxylation generate coordinatively unsaturated $ {\text{Ni}}^{2 + } $ that interact with isobutene during the oligomerization reaction. The formation of lower-valent nickel ions ( $ {\text{Ni}}^{x + } ,x\; \le\; 1 $ ) was demonstrated by in situ DRIFTS using CO as a probe molecule and by XPS measurements. Formation of a binuclear bridging carbonyl complex, $ [{\text{Ni}}({\text{CO}})^{ + } ]_{2} $ suggested that some lower-valent nickel species were formed via in situ reduction by isobutene. Analysis of Ni 2p photolines indicated the appearance of a new lower-valent nickel species ( $ {\text{Ni}}^{x + } ,x \;\le\; 1 $ ) during the course of isobutene oligomerization. Hence it is plausible that lower-valent nickel species might act as the active center for the oligomerization reaction, while the SO₄ ^2? ions enhance the acidity of the Lewis acid sites on the surface and assist in the adsorption of reactant molecules on the surface.     

Improving the dispersion of CeO2 on γ-Al2O3 to enhance the catalytic performances of CuO/CeO2/γ-Al2O3 catalysts for NO removal by CO

Acetic acid (HAc) aqueous was used as solvent in wetness impregnation to prepare CeO₂-modified γ-Al₂O₃ support. With the help of HAc, the dispersion of CeO₂ on γ-Al₂O₃ is significantly improved and the size of CeO₂ nanoparticles can be controlled through tuning the concentration of HAc aqueous. XPS analysis shows that the percentages of Ce^3 + in CeO₂ nanoparticles will vary with the size. Then we load CuO on the as-prepared CeO₂-modified γ-Al₂O₃ support and choose NO reduction with CO as a probe reaction to investigate the influences of impregnation solvent on the catalytic properties. The results demonstrate that the CuO/CeO₂/γ-Al₂O₃ prepared in the solvent with volume ratio of 20:1 (H₂O:HAc) has the highest activity in NO + CO reaction. Combing the structural characterizations and catalytic performances, we think that the size of the CeO₂ nanoparticles should be a key factor that affects the activities of CuO/CeO₂/γ-Al₂O₃. Furthermore, CuO dispersed on CeO₂ nanoparticles with an average size of ca. 5 nm should be the highest active sites for NO + CO reaction.     

Crystallization of Glasses in the K2O–Nb2O5–SiO2System

The changes in the structure and phase composition of glasses in the K₂O–Nb₂O₅–SiO₂system upon their heat treatment in the temperature range 700–800°C are studied by the small-angle X-ray scattering (SAXS) technique and X-ray powder diffraction. It is demonstrated that the crystallization is the primary process giving rise to microinhomogeneities in glasses due to heat treatment. Nanocrystals of an unidentified niobium-containing phase precipitate in glasses with the formation of regions with a decreased content of potassium and niobium oxides. An increase in the duration of heat treatment at the studied temperatures results in an increase in the size of nanocrystals without change in their phase composition. This is accompanied by the disappearance of diffusion zones, which leads to a decrease in the SAXS intensity in the range of small scattering angles and, correspondingly, to a decrease in the light scattering intensity.     

Rh–Sr/Al2O3 Catalyst for N2O Decomposition in the Presence of O2

The improving effect of Sr in the catalytic activity of Rh for N₂O decomposition has been studied under 1,000 ppm N₂O/He and 1,000 ppm N₂O/5% O₂/He (GHSV = 10,000 h^?1). Different techniques have been used for catalysts characterization: TEM, SEM-EDX, XRD, N₂ adsorption at ?196 °C and in situ XPS. Sr favours the Rh dispersion and reduction under reaction conditions, and allows the low temperature removal of N₂O in the presence of O₂ (100% decomposition at 350 °C).     

3D-TEM investigation of the nanostructure of a δ-Al2O3 catalyst support decorated with Pd nanoparticles

The electron tomography technique applied in a quantitative way allowed us to characterize a heterogeneous catalyst made of Pd nanoparticles deposited on a δ-Al(2)O(3) lamellar support. In the first step, high resolution tomographic experiments carried out on several typical areas of support have confirmed the hypothesis of formation of δ-Al(2)O(3) proposed in the literature by the coalescence of lateral facets of the γ-Al(2)O(3) precursor. A bimodal porosity was also observed in the arrangement of δ-Al(2)O(3) platelets. In the second step, the Pd nanoparticles were found preferentially anchored on the lateral facets of δ-Al(2)O(3) platelets or on the defects situated on their basal planes. From a general point of view, we have demonstrated once again that the electron tomography technique implemented with nanometre resolution provides unique insight into the structure, morphology and spatial arrangement of components in a complex 3D nanostructure.     

Experimental determination of the liquidus line in the high Bi2O3 region in the TiO2–Bi2O3 system

Liquidus line in the high-Bi₂O₃-containing region of the TiO₂–Bi₂O₃ system was determined experimentally. The equilibrating and quenching technique with subsequent electron probe microanalyser (SEM-EDS) microanalysis were employed. Based on the data, liquidus line was constructed between 60 and 92 mol% Bi₂O₃. The current results showed a higher solubility of Bi₂O₃ in the liquid phase in equilibrium with the Bi₄Ti₃O₁₂ compound compared with the existing phase diagram. In addition, differential scanning calorimetry (DSC) was used to estimate the transformations covering the composition range from 60 to 95 mol% Bi₂O₃. Further, the phase diagram of the TiO₂–Bi₂O₃ system was calculated using a quasichemical model for the liquid phase. The thermodynamic properties of the intermediate compounds were estimated from the data of TiO₂ and Bi₂O₃ pure solids.     

OH spillover from a γ-Al2O3 support in the partial oxidation of methane over Ru/Al2O3

The microkinetics of the oxidation of methane on Ru/Al₂O₃ is developed using a TAP reactor. The shapes of the response curves of reactants and products are used to identify the elementary reactions and their rate parameters. The support, which strongly adsorbs H₂O, participates in the reaction sequence through its supply of hydroxyl to metal particles by spillover, and this step is of kinetic significance. The relative rates of the elementary reactions that give overall partial oxidation or total oxidation are discussed.     

The Use of Low-pressure Plasma on Enhancing the Attachment of Al2O3 Nanoparticles to Wood–Plastic Composites

Wood–plastic composites (WPC) are widely used for many purposes due to their interesting properties, but they have poor surface adhesion due to the chemical inertness of the matrix. Thus, in this work, the effect of plasma treatment on the WPC was investigated regarding its influence in the aluminum oxide (Al₂O₃) nanoparticles attachment to the surface. WPC were prepared in a polypropylene (PP) matrix, plasma-treated at 100 W for 600 s, and then covered with Al₂O₃ nanoparticles dispersion. The WPC/Al₂O₃ surfaces have been investigated by means of morphology, surface roughness, chemical structure, wettability, and nanohardness. Plasma treatment improved the attachment of Al₂O₃ onto WPC, which was confirmed by the higher presence of aluminum and oxygen-containing functional groups and the reduction of the intensity of peaks of methylene (CH₂) and methyl (CH₃) groups on the WPC surface. The higher surface reactivity of plasma-treated WPC resulted in a better distribution of the nanoparticles over the entire surface. In addition, plasma treatment avoided the formation of coffee-ring phenomenon but it was able to create cone-like structures on the WPC, increasing the surface roughness due to the etching effect and the attachment of Al₂O₃ nanoparticles. Plasma treatment followed by Al₂O₃ nanoparticles attachment increased the wettability, hardness, and elastic modulus of WPC at nanometric scale.     

Influence of a heterolayered Al2O3–ZrO2/Al2O3 ceramic protective overcoat on the high temperature performance of PdCr thin film strain gauges

The application of PdCr thin film strain gauges on gas turbine engines requires protective overcoats to prevent the oxidation of the PdCr sensitive element. In this work, a heterolayered Al₂O₃–ZrO₂/Al₂O₃ ceramic film, which was fabricated by electron beam evaporation, is utilized as a protective overcoat over the PdCr sensitive thin film. The morphology and microstructure of the prepared films indicate that the composite Al₂O₃–ZrO₂ film is smooth and compact, and the interface between the composite Al₂O₃–ZrO₂ film and Al₂O₃ film is crack-free, which contributes to improving the protective performance of the heterolayered Al₂O₃–ZrO₂/Al₂O₃ ceramic protective overcoat at high temperature. Moreover, the PdCr thin film strain gauge with heterolayered Al₂O₃–ZrO₂/Al₂O₃ ceramic film as protective overcoat displays a minimum drift rate of less than 0.09%/h at 800 °C, and excellent cyclic repeatability such that the eight cyclic curves of the relative grid resistance are almost overlapped from room temperature to 800 °C, indicating the excellent protecting performance of the heterolayered Al₂O₃–ZrO₂/Al₂O₃ ceramic overcoat. It also reveals the smallest temperature coefficient of resistance of 155.3 ppm/°C compared to the monolayer Al₂O₃ overcoat and composite Al₂O₃–ZrO₂ overcoat.