Graphite-furnace atomization of phosphorus

The slopes of the ln (absorbance) vs. T^?1 dependences for platform/graphite furnace atomization of phosphorus in the presence of Ni²⁺ or La³⁺ modifiers are measured, and found to be similar to the theoretical slope calculated for isothermal atomization. It is concluded that in both cases the atomization mechanism is the same and is expressed by P_2(gas) ? 2P_(gas); P_(gas) ? P^*_(gas). The atomic absorption signal for phosphorus appears and reaches its maximum later when the atomization is carried out from the platform in the presence of modifiers. Hence atomization takes place under nearly isothermal conditions and is much more efficient, thus providing the best conditions for the determination of phosphorus. Treatment of a deteriorated graphite surface with ZrOCl₂ solution repairs any defects and improves the sensitivity of phosphorus determination.     

Electrothermal atomization of silver in graphite furnaces. Part 2. Effects of copper,ascorbic acid and Triton X-100

The effects of copper, ascorbic acid and Triton X-100 on the atomization process of Ag are presented as a function of the initial mass of analyte and the heating rate of atomization. In general, a double pulse structure is detected, at a heating rate of 300 K s⁻¹, in the absorbance profile and its time derivative. This behavior shows up in the Arrhenius plots as two temperature regions of atomization. In the presence of Cu and Triton X-100, a low atomization energy E_a is obtained in the low temperature region and a high value of E_a, which approaches the heat of vaporization of Ag, is obtained in the high temperature region. However, in the presence of ascorbic acid, two low desorption energies are obtained in both temperature regions, suggesting a higher dispersion of particles owing to the presence of a higher number of active sites. At a heating rate of 700 K s⁻¹, a single atomization step with an atomization energy of 233 kJ mol⁻¹ and a first kinetic order of release is detected in the presence of Cu. However, in the presence of ascorbic acid and Triton X-100, two temperature regions of atomization are obtained from the Arrhenius plots, even though the absorbance profiles look continuous. In these cases, a mass dependent E_a is obtained in the low temperature region, and a low E_a with a first kinetic order of release is obtained in the high temperature region. In summary, the low value of E_a indicates vaporization from disperse particles, whereas the mass dependent, higher value of E_a indicates atomization from small clusters, the size and energy of which increase as the initial mass of Ag increases.The structure of the absorbance profiles and their time derivatives, and also the behavior of the Arrhenius plots, correlate well with those predicted by the two-precursor atomization model proposed in our previous work [1].     

Preparation, morphology and properties of nano-sized Al2O3/polyimide hybrid films

Nano-sized Al₂O₃/polyimide (PI) hybrid films based on 4,4′-oxydianiline (ODA) and pyromellitic dianhydride (PMDA) were prepared by incorporation with different content of nano-sized Al₂O₃ via in situ polymerization. The TEM and SEM micrographs indicated that the Al₂O₃ particles were homogenously dispersed in the polyimide matrix by means of the ultrasonic treatment and the addition of coupling agent. The mechanical properties and thermal stability of the pure PI film can be improved by adequate addition of Al₂O₃. The PI hybrid film was strengthened and toughened simultaneously by the introduction of the well-dispersed Al₂O₃ particles. The PI hybrid films showed improved electrical aging performance as compared with pure PI film. Especially, the PI hybrid films with 10 wt.% of Al₂O₃ content exhibited obviously enhanced electrical aging performance with the time to failure of 3.4 times longer than that of pure PI film. The improved electrical aging performance of the hybrid film was attributed to the nano-sized Al₂O₃ particles highly dispersed in the hybrid film, which confirmed by the investigation of the morphology and the surface composition of PI hybrid film before and after electrical aging.     

The Synthesis of Stable, High Solid Content Alumina Sol

The stable alumina sol with an ASB/water molar ratio of 1:30 could not be obtained via the general peptization process because gelation occurred immediately. With the addition of EAcAc the stability of this sol was greatly improved. The studies using TEM, UV-V is and IR spectra revealed that a surface modification layer was formed around the Al₂O₃ colloidal particle through the chelating reaction of EAcAc with the surface HO-Al groups. The Al₂O₃ colloidal particles were therefore sufficiently capped and the growth of the colloidal particles was effectively prevented.     

Gold catalysts supported on ZnO/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> for low-temperature CO oxidation

Gold catalysts with loadings ranging from 0.5 to 7.0 wt% on a ZnO/Al₂O₃ support were prepared by the deposition–precipitation method (Au/ZnO/Al₂O₃) with ammonium bicarbonate as the precipitation agent and were evaluated for performance in CO oxidation. These catalysts were characterized by inductively coupled plasma-atom emission spectrometry, temperature programmed reduction, and scanning transmission electron microscopy. The catalytic activity for CO oxidation was measured using a flow reactor under atmospheric pressure. Catalytic activity was found to be strongly dependent on the reduction property of oxygen adsorbed on the gold surface, which related to gold particle size. Higher catalytic activity was found when the gold particles had an average diameter of 3–5 nm; in this range, gold catalysts were more active than the Pt/ZnO/Al₂O₃ catalyst in CO oxidation. Au/ZnO/Al₂O₃ catalyst with small amount of ZnO is more active than Au/Al₂O₃ catalyst due to higher dispersion of gold particles.     

Characteristics of Plasma-Electrolytic Oxide Coatings Formed on Aluminum and Titanium in Electrolytes with Siloxane Acrylate and Particles of Vanadium,Boron, and Aluminum Oxides

It is shown that aqueous suspension-emulsion electrolytes containing sodium silicate, siloxane-acrylate emulsion, and dispersed particles of oxides are promising for direct synthesis by the plasma-electrolytic oxidation method of coatings with multicomponent composition on titanium and aluminum. The formation processes, composition, and structure of the coatings were studied in electrolytes with 1–4-μm particles of V₂O₅, B₂O₃, or Al₂O₃. The average content of metals and nonmetals of dispersed particles in the surface part of the coatings is ~1–2 at %. The coatings have a developed surface morphology and contain in the surface part up to 50–73 at % carbon.     

Investigations on the electrochemical preparation of gold–nanoparticle composites

The role of electrical charges in the double layers of the electrode and in particles during the electrochemical preparation of dispersion coatings was studied for the systems Au/diamond and Au/Al₂O₃. The surface charge of the electrode under the conditions of electroplating will depend on the potential of zero charge (p.z.c.). For the nanoscaled particles the sign of the surface charge was estimated from the zeta potential in dilute solutions. Successful inclusion of Al₂O₃ and diamond nanoparticles was observed when the particles and the electrode were oppositely charged. The Vickers hardness of the layers was increased by the codeposition of Al₂O₃, whereas it decreased in the case of nanodiamond.Presented at the 3rd International Symposium on Electrochemical Processing of Tailored Materials held at the 53rd Annual Meeting of the International Society of Electrochemistry, 15–20 September 2002, Düsseldorf, Germany     

Eliminated Phototoxicity of TiO2 Particles by an Atomic‐Layer‐Deposited Al2O3 Coating Layer for UV‐Protection Applications

We demonstrate the conformal coating of an ultrathin Al₂O₃ layer on TiO₂ nanoparticles through atomic layer deposition by using a specifically designed rotary reactor to eliminate the phototoxicity of the particles for cosmetic use. The ALD reactor is modified to improve the coating efficiency as well as the agitation of the particles for conformal coating. Elemental and microstructural analyses show that ultrathin Al₂O₃ layers are conformally deposited on the TiO₂ nanoparticles with a controlled thickness. Rhodamine B dye molecules on Al₂O₃‐coated TiO₂ exhibited a long life time under UV irradiation, that is, more than 2 h, compared to that on bare TiO₂, that is, 8 min, indicating mitigation of photocatalytic activity by the coated layer. The effect of carbon impurities in the film resulting from various deposition temperatures and thicknesses of the Al₂O₃ layer on the photocatalytic activity are also thoroughly investigated with controlled experimental condition by using dye molecules on the surface. Our results reveal that an increased carbon impurity resulting from a low processing temperature provides a charge conduction path and generates reactive oxygen species causing the degradation of dye molecule. A thin coated layer, that is, less than 3 nm, also induced the tunneling of electrons and holes to the surface, hence oxidizing dye molecules. Furthermore, the introduction of an Al₂O₃ layer on TiO₂ improves the light trapping thus, enhances the UV absorption.     

Surface reactions and the effects of oxygen on Pb atomization in graphite furnace atomic absorption spectrometry

Summary Previous papers have shown a pronounced shift in appearance temperatures of Pb as a result of O₂ in the system. This paper briefly summarizes the surface chemistry occurring on graphite as a result of exposure to O₂. Chemisorbed oxygen and an altered surface are suggested as the cause for the pulse shift of the Pb absorbance signal. A significant shift with an oxygenated surface but no gas phase O₂ present supports this conclusion. Time and spatially resolved absorbance traces suggest multiple release processes and readsorption of Pb on the surface. Pb/O₂ gas phase reactions do not appear to significantly alter the atomization efficiency and cannot explain the observed shifts. Similarly, O₂/Pb _x O _y(s) reactions cannot account for the first shot back and may play only a secondary role in the presence of O₂ in the gas phase. It was also observed that a significant (> 30%) amount of Pb remained on the surface after the solution was deposited and withdrawn 10 s later. This is attributed to binding of Pb to surface functionalities before the sample is desolvated.

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Oberflächenreaktionen und Wirkungen von Sauerstoff auf die Blei-Atomisierung in der Graphitofen-AAS

Zusammenfassung Vorangegangene Untersuchungen haben eine deutliche Verschiebung der Erscheinungstemperatur von Blei unter dem Einfluß von Sauerstoff im System gezeigt. In dieser Arbeit werden die Oberflächenreaktionen am Graphit unter Sauerstoffeinwirkung zusammenfassend diskutiert. Als Ursachen für die Pulsverschiebung des Bleisignals wurden der chemisorbierte Sauerstoff sowie Veränderungen der Oberfläche gefunden. Eine signifikante Verschiebung bei oxygenierter Oberfläche aber ohne gasförmigen Sauerstoff unterstützt diesen Schluß. Zeitlich und räumlich aufgelöste Absorptionsspuren deuten auf multiple Freisetzungsprozesse und Re-adsorption von Blei an der Oberfläche. Pb/O₂-Reaktionen in der Gasphase scheinen die Atomisierungswirkung nicht signifikant zu beeinflussen und können die beobachteten Verschiebungen nicht erklären. Ebenso können auch die O₂/Pb _x O _y(s)-Reaktionen nicht den first shot back erklären und spielen vielleicht nur eine sekundäre Rolle in Gegenwart von O₂ in der Gasphase. Es wurde ebenfalls beobachtet, daß ein beträchtlicher Anteil des Bleis (> 30%) an der Oberfläche zurückblieb, wenn die Lösung eingebracht und nach 10 s wieder entfernt wurde. Dies wird der Bindung von Blei an Oberflächenfunktionen vor der Desolvatation der Probe zugeschrieben.

     

超声改性的CuO/Al2O3-MgO催化剂结构 及其超低浓度甲烷催化燃烧性能

采用普通浸渍和超声改性的方法分别制备了CuO/Al₂O₃-MgO催化剂,用于超低浓度甲烷的催化燃烧,并利用SEM、XRD、XPS、H₂-TPR等技术对催化剂进行表征,研究了超声改性作用对催化剂的结构和性能的影响.结果表明,与普通浸渍法制备的催化剂相比,在超声改性的CuO/Al₂O₃-MgO催化剂上,甲烷的转化率得到提高,燃烧特征温度降低.随着超声时间的延长和超声功率的增加,催化剂的催化活性均呈现先增大后减小的趋势;催化剂制备的最佳超声工况为功率150 W、时间20 min.超声改性可使催化剂的比表面积和孔容积增大,表面催化活性较高的Cu⁺浓度增加,活性组分CuO由晶相向非晶相转变、分散度增大,晶粒粒径变小、分布更均匀;这使得甲烷催化燃烧的表观活化能下降、催化剂活性得到增强.     

High photocatalytic activity and stability for decomposition of gaseous acetaldehyde on TiO2/Al2O3 composite films coated on foam nickel substrates by sol-gel processes

A set of anatase titanium dioxide (TiO₂) films coated on foam nickel that modified by Al₂O₃ films as transition layer (indicated as TiO₂/Al₂O₃ films) were synthesized via sol-gel route. The bulk and surface properties of the TiO₂/Al₂O₃ films were characterized by thermal gravimetric and differential scanning calorimetry (TG-DSC), X-ray diffraction (XRD), field-emission scanning electron microscope (FE-SEM), and BET. The photocatalytic activities of TiO₂/Al₂O₃ films were investigated based on the degradation of gaseous acetaldehyde under ultraviolet (UV) irradiation. The foam nickel is a promising substrate material in practical applications because of its excellent hydrodynamic properties for gas passing. The TiO₂/Al₂O₃ composite films showed much higher photocatalytic activity and stability for degradation of gaseous acetaldehyde than the onefold TiO₂ films. The significant enhancement in photocatalytic activity and stability can be ascribed to the coating of Al₂O₃ transition layer, which concentrates the target substances around TiO₂ particles and increases the specific surface area (SSA) of the substrate (the SSAs of bare foam nickel and Al₂O₃ modified foam nickel are 0.12 and 113.7 m²/g, respectively) to provide more sites for TiO₂ loading.     

Pentacoordinated Al3+‐Stabilized Active Pd Structures on Al2O3‐Coated Palladium Catalysts for Methane Combustion

Supported Pd catalysts are active in catalyzing the highly exothermic methane combustion reaction but tend to be deactivated owing to local hyperthermal environments. Herein we report an effective approach to stabilize Pd/SiO₂ catalysts with porous Al₂O₃ overlayers coated by atomic layer deposition (ALD). ²⁷Al magic angle spinning NMR analysis showed that Al₂O₃ overlayers on Pd particles coated by the ALD method are rich in pentacoordinated Al³⁺ sites capable of strongly interacting with adjacent surface PdO_x phases on supported Pd particles. Consequently, Al₂O₃‐decorated Pd/SiO₂ catalysts exhibit active and stable PdO_x and Pd–PdO_x structures to efficiently catalyze methane combustion between 200 and 850 °C. These results reveal the unique structural characteristics of Al₂O₃ overlayers on metal surfaces coated by the ALD method and provide a practical strategy to explore stable and efficient supported Pd catalysts for methane combustion.     

Preparation of highly active and reusable heterogeneous Al2O3–Pd catalysts by the sol–gel method using bayberry tannin as stabilizer

A novel heterogeneous Al₂O₃–Pd catalyst has been prepared by the sol–gel method; bayberry tannin (BT) was used as stabilizer to prevent the migration and aggregation of Pd species during calcination. According to N₂ adsorption/desorption determination, Al₂O₃–Pd has a mesoporous structure and its specific area is as high as 336.5 m²/g. Transmission electron microscopy observation indicated that the size of the Pd particles was greatly reduced by the presence of BT. On the basis of X-ray photoelectron spectra analysis, it was found that the most of Pd nanoparticles were dispersed in the pores, implying that BT can prevent migration of Pd particles from the pores to the outer surface of Al₂O₃ during calcination. For comparison, Al₂O₃–Pd^* was prepared by the sol–gel method but without use of BT. In the hydrogenation of acrylic acid, Al₂O₃–Pd had high catalytic activity and excellent reusability compared with commercial and traditionally prepared heterogeneous Pd catalysts. The turnover number of Al₂O₃–Pd is as high as 11,328.0 mol/mol after recycling seven times, which is much higher than that of a commercial Pd–C catalyst (8048.0 mol/mol).     

Surface testing of a tungsten atomizer

This paper deals with the structure and surface changes of a tungsten atomizer. Atomizers made by Metallwerk Plansee for the Czech equipment WETA 90 were studied. Their effect on the height and shape of the peaks of absorption signals was investigated in dependence on number of atomization firings. The influence of various sample matrices on material changes and the evaporation of tungsten during the atomization cycle were also studied. A relationship was found between sensitivity changes and surface quality in dependence on the number of firings carried out. Good stability of sensitivity is guaranteed if the right thermal conditioning process of the atomizer is used. The influence of 4 mol dm⁻¹ HNO₃, HCl, H₂SO₄ and HC1O₄ and 5% H₂O₂ on the corrosion of the atomizer surface was investigated, and significant corrosion was observed only for H₂SO₄ and H₂O₂. The concentration of free tungsten atoms was measured from the absorbance at the tungsten 255.1 nm line (bandpass 0.1 nm) and was significantly registered over 3000°C. No influence of the concentration of hydrogen in the argon protective atmosphere on this parameter was observed.     

Effect of ultra-fine gold particle addition to metal oxides in ethylene oxidation

Oxidation of ethylene was carried out over alumina-supported metal oxide catalysts and highly dispersed gold catalysts, respectively, under atmospheric pressure. The ethylene was completely oxidized to produce carbon dioxide and water with both metal oxide and gold catalysts. The activity of gold catalyst prepared by deposition method was much higher than that of supported metal oxide catalysts. Ultra-fine gold particles on Co₃O₄ were more active than on Al₂O₃. Fe₂O₃/Al₂O₃ and MnO₂/Al₂O₃ catalysts were more active than MoO₃/Al₂O₃ catalyst. The activity of the supported metal oxide catalysts was greatly enhanced by addition of gold particles. It was therefore considered that gold particles promote dissociative adsorption of oxygen and the adsorbed oxygen reacts with adsorbed ethylene on support adjacent to the active site.     

Effect of the composition of the reaction atmosphere on the thermal stability of highly dispersed gold particles on an oxide support (Au/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> system)

Metal gold particles were supported onto the surface of aluminum oxide by physical vapor deposition. The effects of thermal treatments at 30?800°C both in a vacuum and in an atmosphere of O₂ (5 mbar), CO (5 mbar), or a mixture of CO + O₂ (5 mbar of each) on the samples of Au/Al₂O₃ were studied by X-ray photoelectron spectroscopy. An increase in the Au4f line intensity in the course of gold deposition was accompanied by a shift of this line toward smaller binding energy. Upon the supporting of a maximum quantity of gold, the binding energy E _b(Au4f _7/2) became smaller than the value characteristic of the bulk metal. It was hypothesized that this can be explained by the formation of negatively charged Au^δ? particles due to electron density transfer from the support to the particles of gold. In the course of the heating of Au/Al₂O₃ in a vacuum or in a reaction atmosphere, the agglomeration of small gold particles occurred; this fact manifested itself in a decrease in the atomic ratio [Au]/[Al]. In all of the atmospheres, the Au particles supported on Al₂O₃ exhibited high thermal stability; considerable changes in the ratio [Au]/[Al] were observed only at temperatures higher than 600°C.     

乙烷氧化脱氢用Ni/Al2O3催化剂中活性镍物种前驱体（英文）

Ni/Al2O3 catalysts for oxidative dehydrogenation(ODH) of ethane were prepared by impregnation of Al2O3 with nickel acetate or nickel nitrate,and by mechanical mixing of NiO and Al2O3.The Ni-based catalysts were characterized by N2 adsorption-desorption,X-ray diffraction,diffuse reflectance UV-visible diffuse reflectance spectroscopy,and temperature-programmed reduction of hydrogen.The results showed that formation of crystalline NiO particles with a size of < 8 nm and/or non-stoichiometric NiO species in the Ni/Al2O3 catalysts led to more active species in ODH of ethane under the investigated reaction conditions.In contrast,tetrahedral Ni species present in the catalysts led to higher selectivity for ethene.Formation of large crystalline NiO particles(22-32 nm) over Ni/Al2O3 catalysts decreased the selectivity for ethene.     

Multiply Confined Nickel Nanocatalysts Produced by Atomic Layer Deposition for Hydrogenation Reactions

To design highly efficient catalysts, new concepts for optimizing the metal–support interactions are desirable. Here we introduce a facile and general template approach assisted by atomic layer deposition (ALD), to fabricate a multiply confined Ni‐based nanocatalyst. The Ni nanoparticles are not only confined in Al₂O₃ nanotubes, but also embedded in the cavities of Al₂O₃ interior wall. The cavities create more Ni–Al₂O₃ interfacial sites, which facilitate hydrogenation reactions. The nanotubes inhibit the leaching and detachment of Ni nanoparticles. Compared with the Ni‐based catalyst supported on the outer surface of Al₂O₃ nanotubes, the multiply confined catalyst shows a striking improvement of catalytic activity and stability in hydrogenation reactions. Our ALD‐assisted template method is general and can be extended for other multiply confined nanoreactors, which may have potential applications in many heterogeneous reactions.     

Plasma Assisted Synthesis and Physicochemical Characterizations of Ni–Co/Al2O3 Nanocatalyst Used in Dry Reforming of Methane

To assess the effects of plasma treatment a Ni–Co/Al₂O₃ nanocatalyst (10 % Ni and 3 % Co) was prepared via impregnation method followed by treatment with a non-thermal plasma to be investigated in a catalytic dry reforming of methane. The impregnated and plasma-treated nanocatalysts were characterized using XRD, FESEM, EDX, TEM, BET, FTIR, and XPS techniques. The XRD patterns confirmed the presence of nickel as NiO and NiAl₂O₄ and cobalt as Co₃O₄ on alumina support. Small NiO, NiAl₂O₄, and Co₃O₄ crystals observed in plasma-treated nanocatalyst, exhibited a good dispersion of active phase in this catalyst. The average particles size in plasma-treated sample obtain by FESEM micrograph were shown to be smaller than that of impregnated sample and the morphology was more homogenous and relatively agglomeration-free in plasma-treated Ni–Co/Al₂O₃ nanocatalyst. According to BET analysis, specific surface area of plasma-treated sample was 58 % higher than the non-treated catalyst. TEM analysis showed that particles of active phase were fairly small and well-dispersed on Al₂O₃ as a result of the plasma treatment. Better dispersion of active metal on the surface of plasma-treated sample was confirmed by XPS analysis. The plasma-treated sample showed higher yield and conversion at all temperature ranges investigated and was more resistant to coke formation compared to the non-treated sample. The results from the characterization and reaction studies suggests that plasma treatment may be a promising method for obtaining more active and stable nanocatalysts for dry reforming of methane.     

Monolithic FeO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts for ammonia oxidation and nitrous oxide decomposition

(1.2–8.3)%FeO_х/Al₂O₃ monolith catalysts have been prepared by impregnating alumina with aqueous solutions of iron(III) nitrate and oxalate and have been tested in NH₃ oxidation and in the selective decomposition of N₂O in mixtures resulting from ammonia oxidation over a Pt–Rh gauze pack under conditions of nitric acid synthesis (800–900°C). In the case of the support calcined at 1200°C, the catalyst is dominated by bulk Fe₂O₃ particles localized on the Al₂O₃ surface. The activity of these samples in both reactions decreases with a decreasing active component content, thus limiting the potential of Fe₂(C₂O₄)₃ · 5H₂O, an environmentally friendlier but poorly soluble compound, as a substitute for Fe(NO₃)₃ · 9H₂O. Decreasing the support calcination temperature to 1000°C or below leads to the formation of a highly defective Fe–Al–O solid solution in the (1.2–2.7)%FeO_х/Al₂O₃ catalysts. The surface layers of the solid solution are enriched with iron ions or stabilize ultrafine FeO_х particles. The catalytic activity of these samples in both reactions is close to the activities measured for ~8%FeO_х/Al₂O₃ samples prepared using iron nitrate.