Gel-casted porous Al<Subscript>2</Subscript>O<Subscript>3</Subscript> ceramics by use of natural fibres as pore developers

An approach using ceramic shaping by gel-casting and addition of natural tropical fibres as burnable pore developers has been explored for development of porous alumina materials with predetermined pore structures. The fibres used have been characterized in terms of size, shape, water uptake and surface charge. The degree of fibres loading in slurry has been varied. It has been shown that the amount of added fibres correlates well with the measured porosity, the shape of the developed pores however deviating slightly with that of the introduced fibres. The ceramic bodies have been characterised in terms of porosity, shrinkage and flexural strength. It could be assumed that at fibres amount in slurry above 30% V, an open porosity appears which is accompanied by a sharp drop in strength. In order to explore the benefits of the gel-casting method for complex bodies development, two key issues need to be addressed: air evacuation prior to casting and lowering slurry viscosity at fibre loadings higher than the tested ones. For reaching the latter objective, surface modification of fibres has been undertaken.     

Effect of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-ZrO<Subscript>2</Subscript> xerogel support on hydrogen production by steam reforming of LNG over Ni/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-ZrO<Subscript>2</Subscript> catalyst

An Al₂O₃-ZrO₂ xerogel (AZ-SG) was prepared by a sol-gel method for use as a support for a nickel catalyst. The Ni/AZ-SG catalyst was then prepared by an impregnation method, and was applied to hydrogen production by steam reforming of LNG. A nickel catalyst supported on commercial alumina (A-C) was also prepared (Ni/A-C) for comparison. The hydroxyl-rich surface of the AZ-SG support increased the dispersion of nickel species on the support during the calcination step. The formation of a surface nickel aluminate-like phase in the Ni/AZ-SG catalyst greatly enhanced the reducibility of the Ni/AZ-SG catalyst. The ZrO₂ in the AZ-SG support increased the adsorption of steam onto the support and the subsequent spillover of steam from the support to the active nickel sites in the Ni/AZ-SG catalyst. Both the high surface area and the well-developed mesoporosity of the Ni/AZ-SG catalyst improved the gasification of adsorbed surface hydrocarbons in the reaction. In the steam reforming of LNG, the Ni/AZ-SG catalyst showed a better catalytic performance than the Ni/A-C catalyst. Moreover, the Ni/AZ-SG catalyst showed strong resistance toward catalyst deactivation.     

Ultrafine Si/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> composites obtained by combining methods of mechanical activation and self-propagating high-temperature synthesis

Mechanical activation of a mixture of silicon oxide and aluminum is studied by methods of infrared spectroscopy, differential thermal analysis, and x-ray diffraction. If a SiO₂/Al mechanocomposite is used as a precursor, then a Si/Al₂O₃ composite with a small grain size and a uniform distribution of the components can be obtained by the method of self-propagating high-temperature synthesis.     

Preparation and application of zeolite beta with super-low SiO<Subscript>2</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> ratio

This paper presents the direct synthesis of super-low SiO₂/Al₂O₃ ratio zeolite beta molecular sieve through a novel route, by which some of aluminium species are added during crystaling process. The IR results show that with the increase of aluminium content in the framework, the frequency of the band in the range of framework vibration (1060–1090 cm⁻¹) shifts to the lower wave-number; the BET surface-area decreases and the basicity of zeolite becomes stronger. In a second step, new adsorbents were obtained by solid-state ion exchanging zeolite beta with Cu(I), Ag(I) cations. The deep-desulfurization (sulfur levels of <1 ppmw) tests were performed using fixed-bed adsorption technique, the sulfur content of the treated and untreated gasoline was analyzed by microcoulometry. The experimental results show that the desulfurization performance of sorbents decreases in order: Cu(I)beta > Ag(I)beta > Na-beta. The best sorbent, Cu(I)beta, has breakthrough adsorption capacities of 0.236 mmolS/g of sorbent for model gasoline.     

Synthesis and properties of flux-cast refractories in the Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-MgO-B<Subscript>2</Subscript>O<Subscript>3</Subscript> system

Details are given of the synthesis and testing of flux-cast refractory materials in the alumina-rich region of the Al₂O₃-MgO-B₂O₃ system; XRD and petrography indicate that the main structure-forming phases are corundum and magnesian spinel. In subordinate amounts there are the boroaluminate 9Al₂O₃·2B₂O₃ and the previously unknown compound 4Al₂O₃·MgO·2B₂O₃, whose composition has been established by microprobe analysis. Corrosion tests showed that three-component systems containing magnesium and boron oxides at levels of 5–10% do not increase the corrosion resistance of refractories in molten sodium-calcium-silicate glass and electrovacuum borosilicate glass. __________ Translated from Novye Ogneupory, No. 3, pp. 161–163, March, 2008.     

Physicochemical properties of nanocrystalline composites based on ZrO<Subscript>2</Subscript>, Al<Subscript>2</Subscript>O<Subscript>3</Subscript>, and rare-earth oxides

Powder precursors have been prepared by means of the sol-gel technique and codeposition, and nanoceramics in the ZrO₂-Al₂O₃-rare-earth (RE) oxide system (RE = Ce, Sc, or Y) based on them have been obtained. Physicochemical properties of the resulting ceramic composites have been investigated. The energy model for oxygen-ionic transport processes in a solid solution based on ZrO₂, which relies on computer simulation procedure, has been proposed, and the structural, strength, and electrophysical characteristics of the solid solution have been calculated. The obtained materials are promising as high-melting electrochemical sensors in molten oxides.     

Highly efficient removal of phenol from aqueous solutions using graphene oxide/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> composite membrane

To achieve superior separation performance in the phenol aqueous solutions treatment, a novel graphene oxide/Al₂O₃ composite membrane was prepared by a spin coating process. The microstructure measurement shows that the composite membrane has a multilayer structure and graphene oxide has been tightly coated on the surface of the Al₂O₃ membrane interlayer homogeneously. During the treatment of phenol aqueous solutions, the permeation flux and phenol rejection of the composite membrane were investigated. The results show the permeation flux of the membrane is about 1.153 L m^?2 h^?1 bar^?1 and the phenol rejection of the membrane increases to 99.9% when the phenol concentration is 0.01 g L^?1. The high phenol rejection of the composite membrane is mainly attributed to the physical sieving, the solution–diffusion effect and the hydrophobic nature of graphene oxide. All these results indicate the GO/Al₂O₃ composite membrane is a suitable material for the removal of phenol from aqueous solutions in environmental pollution management.     

Viscosity affected by nanoparticle aggregation in Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-water nanofluids

An investigation on viscosity was conducted 2 weeks after the Al₂O₃-water nanofluids having dispersants were prepared at the volume concentration of 1-5%. The shear stress was observed with a non-Newtonian behavior. On further ultrasonic agitation treatment, the nanofluids resumed as a Newtonian fluids. The relative viscosity increases as the volume concentrations increases. At 5% volume concentration, an increment was about 60% in the re-ultrasonication nanofluids in comparison with the base fluid. The microstructure analysis indicates that a higher nanoparticle aggregation had been observed in the nanofluids before re-ultrasonication.     

Europium(II) in glasses of the Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript>-MnO-Eu<Subscript>2</Subscript>O<Subscript>3</Subscript> system

Triply and doubly charged states of europium are revealed by ¹⁵¹Eu Mössbauer spectroscopy in the structure of glasses of the composition (mol %) 19.5Al₂O₃, 31.5SiO₂, 26.5MnO, and 22.5Eu₂O₃. The isomer shifts in the Mössbauer spectra of Eu³⁺ and Eu²⁺ ions in the structure of glasses differ from the isomer shifts in the spectra of the Eu₂O₃ and EuO compounds. This difference is explained by the fact that the electron density at ¹⁵¹Eu nuclei is affected by the manganese and aluminum atoms, which are not bound directly to the europium atoms. The broadening of the spectra of the Eu²⁺ ions in glasses is caused by the nonuniform isomer shift.     

The influence of the structural and electronic characteristics of palladium on the activity and selectivity of Pd/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and Pd-Co/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts for the hydrogenation of acetylene hydrocarbons

The influence of the structural and electronic characteristics of nonpromoted and cobalt-promoted Pd catalysts on their adsorption and catalytic properties is studied. It is shown that the conversion of vinylacetylene depends on the dispersion of palladium for both types of catalysts synthesized from acetate and acetylacetonate complexes. The palladium acetylacetonate catalysts have a higher palladium dispersion than the samples obtained from acetate complex solutions, thus leading to a higher conversion of vinylacetylene. It is established that the selectivity of vinylacetylene conversion into 1,3-butadiene on palladium acetate and acetylacetonate catalysts depends on the state of the 3d orbitals of surface Pd atoms. The palladium acetate catalysts are characterized by a higher electron density on the 3d orbital in comparison with the acetylacetonate samples, thus producing higher selectivities of vinylacetylene conversion into 1,3-butadiene. The introduction of cobalt into Pd/δ-Al₂O₃ catalyst synthesized from acetylacetonate complex leads to the formation of bimetallic Pd-Co particles, in which Pd atoms have higher electron density than those in the nonpromoted Pd/δ-Al₂O₃ catalyst, due probably to the donation of electron density from promoter atoms, with a resulting decline in the adsorption ability of bimetallic particles with regard to 1,3-butadiene and hydrogen. As a consequence, the selectivity of vinylacetylene conversion into 1,3-butadiene increases. Requirements for the size, dispersion, and electronic characteristics of the active component in the catalysts for the selective hydrogenation of vinylacetylene are formulated, and two techniques for their synthesis are proposed.     

Uniform color coating of multilayered TiO<Subscript>2</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> films by atomic layer deposition

Thin film optics, based on light interference characteristics, are attracting increasing interest because of their ability to enable a functional color coating for various applications in optical, electronic, and solar industries. Here, we report on the dependence of coloring characteristics on single-layer TiO₂ thicknesses and alternating TiO₂/Al₂O₃ multilayer structures prepared by atomic layer deposition (ALD) at a low growth temperature. The ALD TiO₂ and Al₂O₃ thin films were studied at a low growth temperature of 80°C. Then, the coloring features in the single-layer TiO₂ and alternating TiO₂/Al₂O₃ multilayers using both the ALD processes were experimentally examined on a TiN/cut stainless steel sheet. The Essential Macleod software was used to estimate and compare the color coating results. The simulation results revealed that five different colors of the single TiO₂ layers were shown experimentally, depending on the film thickness. For the purpose of highly uniform pink color coating, the film structures of TiO₂/Al₂O₃ multilayers were designed in advance. It was experimentally demonstrated that the evaluated colors corresponded well with the simulated color spectrum results, exhibiting a uniform pink color with wide incident angles ranging from 0° to 75°. This article advances practical applications requiring highly uniform color coatings of surfaces in a variety of optical coating areas with complex topographical structures.     

Reductive amination of ethanol to ethylamines over Ni/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts

Ni(x)/Al₂O₃ (x=wt%) catalysts with Ni loadings of 5–25 wt% were prepared via a wet impregnation method on an γ-Al₂O₃ support and subsequently applied in the reductive amination of ethanol to ethylamines. Among the various catalysts prepared, Ni(10)/Al₂O₃ exhibited the highest metal dispersion and the smallest Ni particle size, resulting in the highest catalytic performance. To reveal the effects of reaction parameters, a reductive amination process was performed by varying the reaction temperature (T), weight hourly space velocity (WHSV), and NH₃ and H₂ partial pressures in the reactions. In addition, on/off experiments for NH₃ and H₂ were also carried out. In the absence of NH₃ in the reactant stream, the ethanol conversion and selectivities towards the different ethylamine products were significantly reduced, while the selectivity to ethylene was dominant due to the dehydration of ethanol. In contrast, in the absence of H₂, the selectivity to acetonitrile significantly increased due to dehydrogenation of the imine intermediate. Although a small amount of catalyst deactivation was observed in the conversion of ethanol up to 10 h on stream due to the formation of nickel nitride, the Ni(10)/Al₂O₃ catalyst exhibited stable catalytic performance over 90 h under the optimized reaction conditions (i.e., T=190 °C, WHSV=0.9 h^?1, and EtOH/NH₃/H₂ molar ratio=1/1/6).     

Enhanced cyclic stability of CO<Subscript>2</Subscript> adsorption capacity of CaO-based sorbents using La<Subscript>2</Subscript>O<Subscript>3</Subscript> or Ca<Subscript>12</Subscript>Al<Subscript>14</Subscript>O<Subscript>33</Subscript> as additives

To improve the stability of CaO adsorption capacity for CO₂ capture during multiple carbonation/calcination cycles, modified CaO-based sorbents were synthesized by sol-gel-combustion-synthesis (SGCS) method and wet physical mixing method, respectively, to overcome the problem of loss-in-capacity of CaO-based sorbents. The cyclic CaO adsorption capacity of the sorbents as well as the effect of the addition of La₂O₃ or Ca₁₂Al₁₄O₃₃ was investigated in a fixed-bed reactor. The transient phase change and microstructure were characterized by X-ray diffraction (XRD) and field emission scanning electron microscopy (FSEM), respectively. The experimental results indicate that La₂O₃ played an active role in the carbonation/calcination reactions. When the sorbents were made by wet physical mixing method, CaO/Ca₁₂Al₁₄O₃₃ was much better than CaO/La₂O₃ in cyclic CO₂ capture performance. When the sorbents were made by SGCS method, the synthetic CaO/La₂O₃ sorbent provided the best performance of a carbonation conversion of up to 93% and an adsorption capacity of up to 0.58 g-CO₂/g-sorbent after 11 cycles.     

Synthetic spinels of the system MgO-Cr<Subscript>2</Subscript>O<Subscript>3</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>

Synthetic spinels of the system MgO-Cr₂O₃-Al₂O₃-Fe₂O₃ are considered and the desirability of organizing their production for the refractory industry is demonstrated. Translated from Novye Ogneupory, No. 6, pp. 32–35, June 2008.     

Effect of Cu promoter and alumina phases on Pt/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> for propane dehydrogenation

We investigated the effects of different Cu weight ratio on θ or γ-Al₂O₃ which were impregnated with platinum in terms of catalytic activity for propane dehydrogenation and physicochemical properties. 1.5 wt% Pt, 0-10 wt% Cu catalyst supported on θ-Al₂O₃ or γ-Al₂O₃ was prepared by incipient wetness co-impregnation. Enhanced Pt dispersion by increasing Cu contents in γ-Al₂O₃ supported catalyst was confirmed via XRD and XPS. Pt and CuO was separated in Pt-Cu/θ-Al₂O₃, but Pt-Cu alloy was identified after reduction treatment. Also, adding Cu in Pt/Al₂O₃ makes catalyst’s acidity lower and this property led to increased propylene yield in propane dehydrogenation. However, Pt₃Cu was not good for yield of PDH, which was confirmed in Pt-10Cu/θ-Al₂O₃ through XRD.     

Catalytic oxidation of methane on CuO/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/FeAlO/FeAl cermet catalysts

The activity of plates of CuO/Al₂O₃/FeAlO/FeAl structured cermet catalysts is compared by varying their alumina content. The catalysts were prepared by impregnation of cermet supports obtained by mechanochemical activation of powder mixtures of an alumina precursor [20–50% (wt.)], iron, and aluminum, followed by hydrothermal treatment and calcination. It is shown that increasing the content of the alumina precursor (product of thermal activation of gibbsite) increases the specific surface area of the support and the mesopore and macropore volumes and reduces its mechanical strength. The content of the active component (CuO) also increases, resulting in an increase in the specific activity of catalyst despite a reduction in the effectiveness of using the active component. The activity of catalysts with a moderate concentration of alumina is sufficient to initiate methane oxidation.