Nano-sized layered aluminium or zinc-manganese oxides as efficient water oxidizing catalysts

Nano-sized layered aluminium or zinc-manganese oxides were synthesized and characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction spectrometry, dynamic light scattering and atomic absorption spectroscopy. These oxides showed efficient water oxidizing activity in the presence of cerium(IV) ammonium nitrate as a non-oxo transfer oxidant. Amounts of dissolved manganese, zinc or aluminium, and water oxidation activities of these oxides were reported and compared with other manganese oxides. A mechanism for oxygen evolution and possible roles for zinc or aluminium ions are also proposed.     

Phase composition of manganese-alumina catalysts for the reactions of deep oxidation

X-ray powder diffraction, transmission electron microscopy and differential dissolution were used for investigation of the phase transformation peculiarities of biphasic manganese-alumina catalysts during their thermal treatment. An effect of interaction between aluminium and manganese oxides depending on the sample preparation procedure was found.     

Influence of aluminium precursor on physico-chemical properties of aluminium hydroxides and oxides

The paper concerns aluminium hydroxides precipitated during hydrolysis of aluminium acetate in ammonia medium, as well as aluminium oxides obtained through their calcination at 550, 900 or 1200°C for 2 h. The following techniques were used for analysing of obtained materials: thermal analysis, IR spectroscopy, X-ray diffraction, low-temperature nitrogen adsorption, adsorption-desorption of benzene vapours and scanning electron microscopy. Freshly precipitated boehmite/pseudoboehmite had high value of S _BET, very good sorption capacity for benzene vapours, developed mesoporous structure and hydrophilic character. After prolonged refluxing at elevated temperature its crystallinity increased which was accompanied by a decrease of specific surface determined from nitrogen adsorption, decrease of sorption capacity for benzene vapours and weakening of the hydrophilic character. Calcination of all hydroxides at the temperature up to 1200°C resulted in the formation of α-Al₂O₃ via transition forms of γ-, δ-and θ-Al₂O₃. The samples of aluminium oxides obtained after calcination at 550 and 900°C were characterised with high values of specific surface area and displayed quite high heat resistance, probably due to a specific morphology of starting hydroxides. The process of ageing at elevated temperature developed thermal stability of aluminium oxides.     

Nanoscale analysis of surface oxides on ZnMgAl hot-dip-coated steel sheets

In this work, the first few nanometres of the surface of ZnMgAl hot-dip-galvanised steel sheets were analysed by scanning Auger electron spectroscopy, angle-resolved X-ray photoelectron spectroscopy and atomic force microscopy. Although the ZnMgAl coating itself is exhibiting a complex micro-structure composed of several different phases, it is shown that the topmost surface is covered by a smooth, homogeneous oxide layer consisting of a mixture of magnesium oxide and aluminium oxide, exhibiting a higher amount of magnesium than aluminium and a total film thickness of 4.5 to 5 nm. Especially by the combined analytical approach of surface-sensitive methods, it is directly demonstrated for the first time that within surface imprints—created by industrial skin rolling of the steel sheet which ensures a smooth surface appearance as well as reduced yield-point phenomenon—the original, smooth oxide layer is partly removed and that a layer of native oxides, exactly corresponding to the chemical structure of the underlying metal phases, is formed.     

Influence of aluminium precursor on physico-chemical properties of aluminium hydroxides and oxides

The process of hydrolysis of aqueous aluminium sulfate was carried on in ammonia medium at 100°C and for different time intervals (0, 20, 39 or 59 h). The products thus obtained were calcined at 550, 900 or 1200°C for 2 h with the aim to obtain aluminium oxides. The materials were studied with the following methods: thermal analysis, IR spectroscopy, X-ray diffraction, low-temperature nitrogen adsorption, adsorption–desorption of benzene vapours and scanning electron microscopy. Freshly precipitated material was an amorphous basic aluminium sulfate which after prolonged refluxing at elevated temperature in a mother liquor underwent a phase transformation into highly crystalline NH₄Al₁₃(SO₄)₂(OH)₆ containing tridecameric unit Al₁₃. It was accompanied by a decrease of specific surface area and the formation of a porous structure less accessible for benzene molecules. Regardless of the duration of the hydrolysis process, all products were characterised with poorly developed porous structure and hydrophilic character. Their calcination at the temperature up to 1200°C resulted in the formation of α-Al₂O₃ via transition forms of γ/η- and δ-Al₂O₃. The samples of aluminium oxides obtained after calcination at 550 and 900°C had higher values of specific surface area than starting materials due to processes of dehydroxylation and desulfurization. The process of calcination up to 900°C was reflected in developing of not only porous structure but also hydrophobic character of prepared materials. The S _BET values calculated for the oxide samples obtained from aged products of hydrolysis at 1200°C were lower than for the analogous sample prepared without the ageing step. It was concluded that prolonged refluxing at elevated temperature of the products of hydrolysis of aluminium sulfate decreased thermal stability of final aluminium oxides.     

Silicate‐based post‐anodic treatment for lithographic application

Sodium silicate solutions are widely used chemicals for a variety of applications. In particular, they are commonly used in pre‐treatments of aluminium alloys as cleaners and corrosion inhibitors. Another application is found in offset printing, where after graining and anodising, a silicate‐based post‐anodic treatment (PAT) is considered to optimise the aluminium plate characteristics. It is, however, not clear what type of interaction takes place between the oxide‐covered aluminium and the silicate solution. In this work, silicate‐based PAT is studied. Different barrier‐type and porous‐type aluminium oxides are silicate‐treated by dipping in a water‐based sodium silicate solution and the effect of time on the deposition is studied. Particular attention is given to the role of rinsing when the alumina surface is washed in water after the silicate treatment. A good understanding of the role of rinsing allows us to obtain information on the characteristics of the silicate layer which is formed after dipping. The surface modifications induced by the silicate treatment on the aluminium oxides were monitored by means of field emission scanning electron microscopy and infrared spectroscopic ellipsometry. Quantitative measurements on the amount of deposited silicate were taken by X‐ray fluorescence, and relative comparisons between different oxides are shown. Auger electron spectroscopy was used to study the in‐depth composition of the silicate deposition. Experiments show a high affinity of the silicate to the anodic oxide film. A thin nanometric chemisorbed (alumino)silicate layer is present on the surface after rinsing, while the physisorbed part of the layer is washed away. Copyright © 2009 John Wiley & Sons, Ltd.     

Syntheses and Characterization of ZSM-5 Zeolites Containing Diethylamine and Ethylenediamine

Syntheses of ZSM-5 zeolites from R-SiO2-Al2O3-H2O-HF(R = diethylamine and ethylenediamine, respectively) were investigated by using the hydrothermal crystallization. The large single crystals of ZSM-5 containing diethylamine and ethylenediamine were synthesized. The ZSM-5 precursors were characterized by means of X-ray powder diffraction, scanning electron microscopy, thermal analysis and electron microprobe analysis. The analysis result of aluminium distribution shows that the interior aluminium content of large crystals of ZSM-5 zeolites is rather low.     

Surface Nanosegregation of Chemical Composition in Complex Oxides

A brief review of theoretical, experimental results in the field of surface nanosegregation of chemical composition of oxides (principal components), stimulated by temperature or other factors, is given. Experimental data, obtained exclusively for monocrystals in situ and post situ by Auger electron spectroscopy, X-ray electron spectroscopy, X-ray spectral microanalysis, and secondary-emission spectroscopy are considered. The model concepts assume a diffusion mechanism of segregation, and the theory parameters contain elastic constants and crystallochemical characteristics of substances. All the oxides investigated are divided into groups with different segregation degrees. The models allow prediction of the character of changes of the surface composition of oxides: segregate type and degree of nonstoichiometry.     

Determining the local coordination of aluminium in cement using electron energy loss near-edge structure

The local site symmetry of aluminium in Al-substituted calcium silicate hydrate phases, similar to those found in hardened Portland cement pastes, has been determined by experimental measurement and theoretical modelling of the electron energy loss near-edge structure associated with the aluminium K-edge measured using parallel electron energy loss spectroscopy in the transmission electron microscope. Changes in the local aluminium environment were observed between different regions of the microstructure which are explained in terms of aluminium substitution into both tetrahedral silicon and octahedral magnesium sites. This spatially-resolved information is in excellent agreement with²⁷Al and²⁹Si magic angle spinning nuclear magnetic resonance data on bulk samples as well as the predictions based upon compositional trends derived from the results of energy dispersive X-ray and electron energy loss elemental microanalysis. In a wider context we wish to stress the complementarity of both spatially-resolved and bulk spectroscopic techniques, which possess differing degrees of sensitivity, in the analysis of materials science samples.     

Analytical characterization of municipal solid waste incinerator fly ash. Part II

The synergy of the micro FT-IR (Fourier Transform-Infrared) and SEM-EDX (Scanning Electron Microscopy-Energy Dispersive X-ray) techniques has been shown to be particularly helpful and effective for the characterization of inorganic compounds in fly ashes. The experimental data obtained by these techniques have been interpreted in comparison with those of other techniques. The presence of calcium carbonate, some sulfates, ammonium nitrate, calcium hydrogen phosphate, some chlorides, some oxides and aluminium silicates have been verified.     

Analytical characterization of municipal solid waste incinerator fly ash

The synergy of the micro FT-IR (Fourier Transform-Infrared) and SEM-EDX (Scanning Electron Microscopy-Energy Dispersive X-ray) techniques has been shown to be particularly helpful and effective for the characterization of inorganic compounds in fly ashes. The experimental data obtained by these techniques have been interpreted in comparison with those of other techniques. The presence of calcium carbonate, some sulfates, ammonium nitrate, calcium hydrogen phosphate, some chlorides, some oxides and aluminium silicates have been verified.     

Nanoscale manganese oxide within Faujasite zeolite as an efficient and biomimetic water oxidizing catalyst

Nanoscale manganese oxides within Faujasite zeolite have been synthesized with a simple method and characterized by scanning electron microscopy, X-ray diffraction spectrometry, N(2) adsorption-desorption isotherms, transmission electron microscopy, and atomic absorption spectroscopy. These oxides showed efficient water oxidizing activity in the presence of cerium(iv) ammonium nitrate as a non-oxo transfer oxidant.     

XRD and TPR Studies of Cu-Al Hydrotalcite Derived Highly Dispersed Mixed Metal Oxides

A series of Cu/Al catalysts, containing different proportions of copper and aluminium, have been prepared by coprecipitation using metal nitrate precursors and Na₂CO₃. The dried precipitate catalyst precursors were characterized by X-ray diffraction (XRD) to show the presence of Cu-Al binary hydrotalcite-like phase. The dried precipitates were calcined at 873 K for 3 h. The calcined catalysts were characterized by XRD and temperature-programmed reduction (TPR) methods to show the presence of unidentified mixed oxides. The results showed that the extent of metal-support interaction increased with copper loading due to the mixed oxides formed from the hydrotalcite-type phase during calcination. High dispersion of the mixed metal oxides was indicated by comparison with similar studies on Cu-Al catalysts, prepared by similar methods, whose precursors showed no hydrotalcite formation.     

Physico-chemical behaviour of hydrated aluminium oxides and associated clay minerals occurring around Pipra,district Sidhi,India

DTA techniques were employed to study the thermal and structural characteristics of hydrated aluminium oxides and aluminous clays of the Pipra pelitic rocks from district Sidhi, India. Detailed microscopic investigations, X-ray and chemical analyses reveal that these clays were derived by the localized weathering of arkosic metasediments. The chemical and normative behaviours have confirmed their formation by the isochemical metamorphism of arkose, aided by a little granitization and followed by minor retrogression. A tentative correlation between the thermal and structural changes of these oxides and clay minerals at various transition temperatures has nicely displayed the presence of kaolinite, diaspore and gibbsite. The exothermic curves of kaolinite confirm the recrystallization. The presence of kaolinite in the clay fractions indicates the detrital origin.     

Nano-sized manganese oxide: a proposed catalyst for water oxidation in the reaction of some manganese complexes and cerium(iv) ammonium nitrate

According to UV-visible spectroscopy, X-ray diffraction spectrometry, dynamic light scattering, Fourier transform infrared spectroscopy, electron paramagnetic resonance spectroscopy, transmission electron microscopy, scanning electron microscopy and X-ray photoelectron spectroscopy, nano-sized manganese oxides are proposed as active catalysts for water oxidation in the reaction of some manganese complexes and cerium(iv) ammonium nitrate.     

Micron-particulate crystalline hexagonal aluminium nitride: a novel, efficient and versatile heterogeneous catalyst for the synthesis of some heterocyclic compounds

The present work reports the application of micron-particulate crystalline hexagonal aluminium nitride/aluminium as a novel, mild acidic and reusable solid heterogeneous catalyst in organic synthesis. The catalyst was synthesized by thermal plasma technique and characterized using X-ray diffractometer and scanning electron microscopy. It catalyzes efficiently many organic transformations such as the synthesis of heterocyclic compounds 2,4,5-triaryl-substituted imidazoles and 2-aryl benzimidazoles.     

介孔/大孔 Al2O3-SiO2复合氧化物的制备与表征

 以正硅酸甲酯和硝酸铝为硅和铝的前驱体,以非离子表面活性剂C16EO10为结构导向剂,采用溶胶-凝胶法制备了双孔结构硅铝复合氧化物材料. 扫描电镜和N2吸附/脱附分析表明,材料具有三维连续大孔和骨架介孔的双孔分布结构. 微米范围的连续大孔结构是由于溶胶-凝胶过程中诱发了Spinodal相分离所致,而骨架介孔的形成则可能是由于表面活性剂分子进入凝胶骨架中,起到构建介孔结构的模板作用. 骨架元素分析结果表明,制备过程中添加的铝大部分进入了凝胶骨架中,取代部分硅而形成酸性硅铝复合氧化物. 采用Hammett指示剂法和吡啶吸附红外光谱法分析了材料的表面固体酸性,结果显示,硅铝复合氧化物属于中强酸,酸强度H0在-5.6～-3.0 之间的酸中心数约为0.35 mmol/g, 并且材料表面的L酸位较为丰富, B酸位相对较少.     

Novel transition-metal-free heterogeneous epoxidation catalysts discovered by means of high-throughput experimentation

Various transition-metal-free oxides have been studied as catalysts for the epoxidation of cyclooctene with hydrogen peroxide by means of high-throughput experimentation. Different boron, aluminium, and gallium oxides were prepared according to various synthesis methods. A number of pure aluminium and gallium oxides showed very good catalytic performances, while the results obtained with boron oxides or mixed oxides were less positive. The best results were obtained with a gallium oxide catalyst, which gave an epoxide yield of 71 % and a selectivity of 99 % after reaction for 4 h at 80 degrees C. Gallium oxides had not been reported previously as active epoxidation catalysts. The use of high-throughput experimentation proved useful both for discovering new active catalysts and for identifying a number of relationships between the synthesis conditions and the catalytic properties of the transition-metal-free oxides.     

Enrichment,incorporation and oxidation of copper during anodising of aluminium–copper alloys

Porous anodic oxides generated on copper‐containing aluminium alloys are less regular than anodic oxides generated on pure aluminium. Specifically, a porous oxide morphology comprising layers of embryo pores, generated by a cyclic process of oxide film growth and oxygen evolution, is generally observed. In this work, the relation between the oxidation behaviour of copper during anodising and the specific porous oxide film morphology was investigated by electrochemical techniques, transmission electron microscopy and Rutherford backscattering spectroscopy (RBS). It was found that the anodising potential determines the oxidation behaviour of copper, and the latter determines the porous oxide morphology. At low voltage, relatively straight pores with continuous cell walls were obtained on Al? Cu alloys, but selective oxidation of aluminium atoms resulted in the occlusion of copper‐containing metallic nanoparticles in the anodic film. At higher potentials, copper oxidation promoted oxygen evolution within the barrier layer, and generation of a less regular film morphology. RBS, performed on Al? Cu alloy specimens, revealed a high volume fraction of copper atoms in the anodic films generated at low potentials and a reduced amount of copper atoms in the anodic oxide films generated at high potentials. Copyright © 2009 John Wiley & Sons, Ltd.     

A new approach to nickel electrolytic colouring of anodised aluminium

Energy dispersive X-ray spectroscopy and scanning electron microscopy were used to analyse nickel on anodic aluminium surfaces after stripping the anodic aluminium oxide. The metal was electroplated at the bottom of the pores of anodised aluminium during electrolytic colouring in solutions without (Watts) and with (citrate) complexing agents, respectively. A relation between the anodic-cathodic processes, changes of the structure and composition of the coating in dependence on the used solution were studied. A morphology study performed after stripping the anodic aluminium oxide revealed the crucial influence of the anodic process/cycle and the complexing agent on the nickel structure on the aluminium surface. Off-time of half-way rectified current influenced the nickel deposition in the pores of anodic alumina negatively.