Properties and structure of NiO-Al2O3 catalysts

Summary It was shown by x-ray and magnetochemical methods that the formation of spinel from coprecipitated nickel and aluminum hydroxides by thermal treatment consists of the following stages: a) formation of a solid solution of nickel and aluminum hydroxides or nickel hydroaluminate by coprecipitation; b) decomposition of the gel and crystal formation in the range 100–250°, accompanied by a sharp decrease in the water content; c) rearrangement of the crystal lattice at 250–300° to a cubic, face-centered spinel-type lattice; d) ordering of the crystal lattice at 300–700° without noticeable redistribution of Ni²⁺ ions, accompanied by a gradual decrease in water content; and e) further ordering of the crystal lattice at 700–1200° with redistribution of Ni²⁺ ions in accordance with the reversibility coefficient of spinel NiAl₂O₄.     

Hydrogen bonds and local symmetry in the crystal structure of gibbsite

First‐principles quantum mechanical calculations of NMR chemical shifts and quadrupolar parameters have been carried out to assign the ²⁷Al MAS NMR resonances in gibbsite. The ²⁷Al NMR spectrum shows two signals for octahedral aluminum revealing two aluminum sites coordinated by six hydroxyl groups each, although the crystallographic positions of the two Al sites show little difference. The presence of two distinguished ²⁷Al NMR resonances characterized by rather similar chemical shifts but quadrupolar coupling constants differing by roughly a factor of two is explained by different character of the hydrogen bonds, in which the hydroxyls forming the corresponding octahedron around each aluminum site, are involved. The Al‐I site characterized by a C_Q = 4.6 MHz is surrounded by OH? groups participating in four intralayer and two interlayer hydrogen bonds, while the Al‐II site with the smaller quadrupolar constant (2.2 MHz) is coordinated by hydroxides, of which two point toward the intralayer cavities and four OH‐bonds are aligned toward the interlayer gallery. In high‐resolution solid‐state ¹H CRAMPS (combination of rotation and multiple‐pulse spectroscopy) four signals with an intensity ratio of 1:2:2:1 are resolved which allow to distinguish six nonequivalent hydrogen sites reported in the gibbsite crystal structure and to ascribe them to two types of structural OH groups associated with intralayer and interlayer hydrogen bonds. This study can be applied to characterize the gibbsite‐like layer—intergallery interactions associated with hydrogen bonding in the more complex systems, such as synthetic aluminum layered double hydroxides. Copyright © 2010 John Wiley & Sons, Ltd.     

Vibration—rotation interaction in the microwave spectrum of NaOH

The rotational transition J = 4 ← 3 of NaOH in a number of vibrational states has been studied in the 100 GHz range. The coupling between the bending and stretching vibrational modes and the contribution of higher order terms in ν₂ and l² to the energy are found stronger for NaOH than for the heavier alkali hydroxides making assignment of some of the observed lines uncertain. In spite of this difficulty careful analysis yielded larger constants for the vibration—rotation interaction. A comparison is made between properties of NaOH and the heavier alkali hydroxides.     

Development of Electroflotation Technology for Extraction of Anionic Surfactants and Nonferrous Metal Ions from Wastewater Produced at Electroplating Industries

Sorption extraction of anionic surfactants NaDDS and NaDBS on freshly formed iron(III) and aluminum(III) hydroxides and on a highly dispersed activated carbon of OU-B brand was experimentally studied. It was shown that NaDDS is the most fully sorbed on Al(OH)₃ and OU-B, whereas on Fe(OH)₃, the maximum sorption is observed for NaDBS. The electroflotation extraction of anionic surfactants and poorly soluble iron(III) and aluminum(III) hydroxides was examined and the influence exerted by the following factors (pH, nature of electrolyte, surfactant concentration) on the degree of extraction of these substances was analyzed. In addition, electroflotation extraction of OU-B in the presence on nonferrous metal hydroxides and surfactants of varied nature from aqueous solutions was performed. The results obtained were used to develop a technological scheme for electroflotation of complex-composition wastewater.     

Layered double hydroxides intercalated with borate anions: Fire and thermal properties in ethylene vinyl acetate copolymer

Fire and thermal properties of ethylene vinyl acetate (EVA) composites prepared by melt blending with layered double hydroxides (LDH) have been studied. Two types of LDHs intercalated with borate anion were prepared using the coprecipitation method and the metals Mg²⁺, Zn²⁺ and Al³⁺. Characterization of the LDHs and the EVA composites was performed using X-ray diffraction, thermogravimetric analysis, and cone calorimetry. Thermal analyses show that the addition of LDHs improves the thermal stability of EVA. Fire properties evaluated using the cone calorimeter were significantly improved in the EVA/LDH composites. The peak heat release rate was reduced by about 40% when only 3% by weight of the LDH was added to the copolymer. Comparison of the fire properties of the LDHs with those of aluminum trihydrate (ATH), magnesium hydroxides (MDH), zinc hydroxide (ZH) and their combinations at 40% loading, reveal that the LDHs were more effective than when MDH and ZH are used alone.     

A novel method for removing aluminum from spallation-produced82Sr

A novel method is presented for the separation of aluminum from strontium by anion exchange in the hydroxide form. When added in acidic solution, aluminum forms Al(OH) ₄ ⁻ and is retained while strontium is eluted as the neutral Sr(OH)₂. The procedure has been used to purify spallation-produced⁸²Sr for use in the⁸²Sr−⁸²Rb radionuclide generator. It has the advantage that the⁸²Sr solution, which must be at basic pH for generator construction, may be neutralized without introducing cations such as Na⁺ and NH ₄ ⁺ . The method may be used to separate any metal which forms an anionic hydroxide from those forming neutral soluble hydroxides.     

Hydration of portland cement in the presence of aluminum-containing setting accelerators

Portland cement hydration in the presence of two different aluminum-containing compounds, highly dispersed amorphous Al(OH)₃ and aqueous solution of aluminum hydroxosulfate Al(OH)_1.78(SO₄)_0.61, was studied by solid-state ²⁷Al and ²⁹Si NMR spectroscopy.     

Adsorption of heavy metals by layered double hydroxides grown in situ on Al foam

We investigated the adsorption of heavy metal ions on a nanostructured coating of zinc-aluminum layered double hydroxides (Zn-Al LDHs) grown on aluminum foam by one-step hydrothermal process. This approach aimed to increase the interactive surface and provide a more practical medium for removal of toxic heavy metals from aqueous media. The foam coated with LDH was characterized by using scanning electron microscopy and X-ray diffraction. After immersion in a copper-rich water solution, X-ray photoelectron spectroscopy demonstrated the occurrence of adsorbed copper on the LDH-coated foam with two oxidation states: particles of metallic copper Cu⁰ with oxidized surface Cu⁺¹. X-ray diffraction showed the presence of Cu⁺² in the LDH structure.     

Effect of surfactants on the structure and texture characteristics of aluminum oxide

The effect of surfactants (polyvinyl alcohol and cetyltrimethylammonium bromide), which were introduced at the aluminum hydroxide synthesis stage, on the structure and texture characteristics of aluminum oxide was studied by a set of physicochemical techniques. The introduction of the above surfactants did not cause considerable changes in the thermal transformations of aluminum hydroxides, but it affected the genesis of the formed carbon. An analysis of the diffuse reflectance spectra and electron micrographs indicated that the aluminum oxide obtained in the presence of polyvinyl alcohol and calcined at 300°C was covered with polyene-type coke. An increase in the treatment temperature to 550°C led to the formation of condensed aromatic coke; in this case, the specific surface area of the sample increased from 125 to 500 m²/g. The samples calcined at 550°C were γ-Al₂O₃ with a unit cell parameter of 7.933 Å and a crystallite size of no more than 30–40 Å. The pore size distribution was bimodal, with maximums at 35–65 and 380–415 Å, regardless of treatment temperature.     

Large pore volume mesoporous aluminum oxide synthesized via nano-assembly

A new nano-assembly approach has been proposed for the preparation of macropore volume mesoporous aluminum oxide supports. Secondary nano-assembly and a frame structure mechanism for large pore volume mesoporous supports have been proposed. In a primary nano-assembly supersoluble micelle, aluminum hydroxide nanoparticles were precipitated in situ in surfactants with a volume balance (VB) less than 1, followed by secondary nano-assembly in linear and cylindrical shapes. The secondary nano-assembly of cylindrical aluminum hydroxides was calcined to form nano cylindrical aluminum oxides. For the formation of macropore volume mesoporous supports, we utilized a frame structure mechanism of mesoporous support, in which the exterior surface of the carrier may not be continuous. This macropore volume support has been used for the hydrotreatment of a residual oil catalyst, which possesses the following physical characteristics: pore volume 1.8–2.7 mL·g⁻¹, specific surface area 180–429 m²·g⁻¹, average pore diameter 17–57 nm, average pore diameter more than 10 nm (81%–94%), porosity 87%–93%, and crush strength 7.7–25 N·mm⁻¹.     

Effect of the nature of the active-component precursor on the properties of Pt/MgAlO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> catalysts in propane and <Emphasis Type="Italic">n</Emphasis>-decane dehydrogenation

The Pt/MgAlO _x catalysts, in which a mixed aluminum–magnesium oxide obtained by the heat treatment of corresponding layered double hydroxides was used as a support, were studied. The effects of the nature of active-component precursors ([PtCl₆]^2–, [PtCl₄]^2–, and [Pt₃(CO)₆] ₆ ^2- ), and the Mg/Al ratio in the support on the anchoring of complexes, the disperse state of platinum, and the properties of the obtained catalysts in the reactions of propane and n-decane dehydrogenation were found.     

Five-coordinate organoaluminum acetylides and crystal structure of the hydrosylate, [Salophen(Bu)Al]2O

The first examples of five coordinate aluminum acetylide compounds chelated by a single ligand are reported in this paper. The combination of L(^tBu)AlCl (where L=Salen (1), Salpen (2), Salophen (3), Salomphen (4)) with LiCCPh in THF at −78 °C leads to the formation of the four acetylides (5-8), LCCPh. These are extremely moisture sensitive and readily hydrolyze to form aluminum hydroxides and with condensation form compounds of formula [L(^tBu)Al]₂O. The hydrosylate [Salophen(^tBu)Al]₂O (9) has been structurally characterized.     

石墨烯/钴镍双金属氢氧化物复合材料的制备及电化学性能研究

采用微波辐射与高温裂解相结合的二步还原法制备石墨烯。二步还原使氧化石墨被充分还原和剥离,所得到的石墨烯有较好的传导性,其比表面达675.4 m2.g-1。以此石墨烯为原料,水热法合成出石墨烯/钴镍双金属氢氧化物复合材料,并考察了复合材料作为超级电容电极材料的电化学性能。研究发现,褶皱的石墨烯纳米片均匀分散在钴镍双金属氢氧化物中,这改善了钴镍双金属氢氧化物的传导性和结构稳定性。在0.25 A.g-1电流密度下,复合材料的比电容量是800.2 F.g-1。当电流密度增加至10 A.g-1,比电容量为386.5 F.g-1,恒电流充-放电500次后比电容量仍能保持99%以上,这些呈示该复合材料具有优良的电化学性能。     

Mechanochemical synthesis of dodecyl sulfate anion (DS−) intercalated Cu-Al layered double hydroxide

Dodecyl sulfate anion (DS⁻) was successfully intercalated into the gallery space of Cu-Al layered double hydroxides (LDH) by a non-heating mechanochemical route, in which basic cupric carbonate (Cu₂(OH)₂CO₃) and aluminum hydroxide (Al(OH)₃) were first dry ground and then agitated in SDS solution under ambient environment. The organics modified Cu-Al LDH showed good adsorption ability toward 2,4-dichlorophenoxyacetic acid (2, 4-D). The prepared samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), CHS elemental analysis and Scanning electron microscopy (SEM). The LDH precursor prepared by ball-milling could directly react with SDS molecules forming a pure phase of DS⁻ pillared Cu-Al LDH, which was not observed with the LDH product through the ion-exchange of DS⁻ at room temperature. The process introduced here may be applied to manufacture other types of organic modified composites for pollutants removal and other applications.     

Adsorption of Cu(II), Cd(II), Pb(II), Cr(VI) by double hydroxides on the basis of Al oxide and Zr, Sn, and Ti oxides

It was studied the equilibrium adsorption and adsorption kinetics of Cu(II), Cd(II), Pb(II), and Cr(VI) by composite hydroxides formed by Me _x O _y · nH₂O and Me_0.4–0.7Al_0.6–0.3O _y · nH₂O, where Me = Zr, Sn and Ti. It was estimated the values of the diffusion coefficients of adsorbed ions Cu(II) and Cr(VI) from kinetic values. It was established that the estimated diffusion coefficients of adsorbed ions Cu(II) are in the range 0.4 × 10⁻¹²–2.5 × 10⁻¹² m²/s for individual hydroxides and 1.2 × 10⁻¹²–2.8 × 10⁻¹² m²/s for double hydroxides. The obtained values of diffusion coefficients Cr (VI) for double hydroxides are 0.1 × 10⁻¹⁰–0.4 × 10⁻¹⁰ m²/s.     

Effect of Peptization on Texture and Physicomechanical Properties of Aluminum Hydroxides

The method of low-temperature adsorption of nitrogen was applied to study structural characteristics of commercial peptized aluminum hydroxides. An increase or decrease in the porometric volume, depending on the nature and concentration of the peptizing agent, was analyzed. The phenomena observed are explained in terms of the mechanism suggested for formation of the pore system in commercial aluminum hydroxides. The dependence of the physicomechanical properties of active aluminum oxide on synthesis conditions and texture characteristics of commercial aluminum hydroxides was studied.     

Polyvinyl alcohol-borate hydrogel containing Prussian blue for surface decontamination

A polyvinyl alcohol (PVA)-borate hydrogel-based strippable surface decontaminant containing an ammonium salt and Prussian blue (PB) was developed for the removal of ¹³⁷Cs from various surfaces. This surface decontaminant can be easily prepared by the simple mixing of commercially available materials, such as PVA, borax, NH₄Cl and PB, in water, and the decontaminant can be peeled off surfaces due to its high elastic property after surface decontamination. The hydrogel displayed an effective removal performance for Cs from painted cement, aluminum, stainless steel, and cement surfaces and a potential for reusability. Therefore, the PB/PVA-borate hydrogel has good potential as a new surface decontaminant.     

Formation of variable-composition iron(III) hydrosilicates with the сhrysotile structure

The process of formation of iron hydrosilicates (Mg²⁺,Fe³⁺)_2–3Si₂O₅(OH)₄ was studied. It was shown that the stage of coprecipitation of magnesium and iron hydroxides in the presence of silica nanoparticles forms poorly crystallized layered Mg–Fe double hydroxides having Fe³⁺ ions in the octahedral sites. Hydrothermal treatment of the mixtures of coprecipitated hydroxides and silica nanoparticles gives rise to layered hydrosilicates, where Fe³⁺ ions occupy both the octahedral (preferentially) and tetrahedral sires. The possibility of the formation and a fairly stable existence of the variable-composition layered hydrosilicate (Mg²⁺,Fe³⁺)_2–3Si₂O₅(OH)₄ was shown to correlate with the stability range of its precursor brucite-like Mg–Fe layered double hydroxide.     

A Layered Cationic Aluminum Oxyhydroxide as a Highly Efficient and Selective Trap for Heavy Metal Oxyanions

Cationic framework materials, especially pure inorganic cationic frameworks that can efficiently and selectively capture harmful heavy metal oxyanions from aqueous solution are highly desired yet scarcely reported. Herein, we report the discovery of a 2D cationic aluminum oxyhydroxide, JU-111, which sets a new benchmark for heavy metal oxyanion sorbents, especially for Cr^VI. Its structure was solved based on 3D electron diffraction tomography data. JU-111 shows fast sorption kinetics (ca. 20 min), high capture capacity (105.4 mg g⁻¹), and broad working pH range (3–10) toward Cr^VI oxyanions. Unlike layered double hydroxides (LDHs), which are poorly selective in the presence of CO₃²⁻, JU-111 retains excellent selectivity for Cr^VI even under a large excess of CO₃²⁻. These superior features coupled with the ultra-low cost and environmentally benign nature make JU-111 a promising candidate for toxic metal oxyanion remediation as well as other potential applications.     

Fixation of radioactive strontium using hydroxides of different metals

Carrier-free radioactive⁸⁹Sr was used to study the adsorption capacities of hydroxides of the metals iron, titanium and manganese at different pH values and at different standing times. The results show that more than 95% of the strontium activity is removed from its solution if the pH is higher than 6.5 for both iron and titanium hydroxides, and higher than 7.8 for manganese hydroxide, when the standing time is higher than 1000 m. In the case of the use of a strontium carrier (1·10^?3 mole/l) it was shown that all the metal hydroxides have the same fixation efficiency for strontium at high pH. Only 300 mg of the metal oxides per litre was enough to remove more than 95% of the strontium activity from its solution.