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Mesoporous γ-Al2O3 materials with high surface area and a narrow pore size distribution were synthesized by facile sol–gel procedure with application of the polymer–colloid complex as a template.

Alumina nano powders have been prepared by a chemical method named combustion synthesis using new fuels. The effect of key factors on the synthesis of nanoparticles was studied and optimized using Taguchi L16 (45 ) array design. The products were characterized by XRD, TGA, EDX, FESEM, and TEM analyses. Results show that aluminum oxide powders had crystal sizes between 7.2 nm and 13 nm and specific surface areas between 21 m2 g-1 and 70 m2 g-1. It was found that there is a good linear correlation (R 2=0.953) between crystallite size and specific surface area of the synthesized γ-alumina. The surface area of the sample prepared under optimum condition was 72 m2 g-1 and its average particle size measured by DLLS was 81 nm. The synthesis of γ-alumina was modified in order to achieve higher specific surface area (123 m2 g-1). A network of nano-fibers was successfully obtained by the modified route. The length and diameter of fibers were about 160 nm and 10 nm respectively.

Washcoating of alumina on cordierite monoliths has been studied with the objective of preparing monoliths with high loadings (>30 wt%). As the alumina loading increased, the competition between spreading and imbibition of the slurry in the monolith channels had a predominant influence on the loading that could be achieved. It was observed that, partial saturation of the washcoat with water allowed the use of concentrated slurries during multiple immersions. The effect of prewetting on the washcoat properties such as adhesion, uniformity, porosity, and reproducibility was investigated.

Alumina–zirconia catalysts for carrying out the hydrolysis of chloropentafluoroethane (CFC-115) were prepared from boemite and γ-alumina, and their deactivation was investigated. On the basis of the characterization results for fresh and used catalysts, catalyst deactivation was attributed to poisoning by fluoride ions, which decreased the acidity of the catalysts. The deactivation of alumina–zirconia catalysts prepared from boemite decreased with increasing alumina content, while the deactivation of alumina–zirconia catalysts prepared from γ-alumina was found to be independent of the alumina content. As the alumina–zirconia catalysts prepared from boemite had two types of acidity, it is suggested that the two types of acidity may be different in the catalyst deactivation for the hydrolysis of CFC-115.

The paper reports a process for synthesis of γ-alumina from kaolin. Kaolin was transformed to meta-kaolin by calcination at 800oC for 2h. γ-alumina powder was synthesized through extracting alumina from meta- kaolin via H2SO4 and meta-kaolin reactions and consequently precipitation in ethanol, which led to form the aluminum sulfate. The precipitated aluminum sulfate was dried and calcined at 900 oC for 2h, which resulted the formation of γ-alumina. The structure of γ-alumina was confirmed by XRD and FTIR and the mean particles size of γ-alumina was determined by SEM to be 0.5 - 0.9 µm. The study revealed the kaolin could be promising material for preparation of γ-alumina.

Accepted: 2013-11-11, 資料番号: SA1140057000

The structure and stability of dimeric Mo(VI) oxide species on γ-alumina are investigated with a periodic DFT approach. A large number of Mo dimers of various geometries, located on the (100) and (110) surfaces of γ-Al2O3, are modeled. The most stable dimeric species on the (100) plane are mixed dioxo−monooxo or double-monooxo species that are 3-, 4-, or 5-fold bonded to the surface. In most cases, the molybdenum atoms are pseudotetrahedrally coordinated. In the case of the (110) surface, the most stable dimeric Mo(VI) forms are double-monooxo species, which are 6- or 5-fold bonded to the support. The coordination of the molybdenum atoms is most frequently a distorted square pyramidal, but distorted octahedral or distorted tetrahedral geometry also happens. The energetic stability of the dimeric Mo(VI) species, relative to the corresponding monomeric Mo(VI) centers, is determined. On the minority (100) surface, the complex−surface interaction is moderate and the dimeric Mo(VI) species are more stable than...

A combined process is proposed for the utilization of local kaolin to produce alumina particles. The applied process is made in two stages: calcination at 700 &deg, C with sodium chloride and leaching with sulfuric followed by hydrochloric acids. The optimal extraction efficiency can be obtained when the conditions are as follows: leaching temperature is at 140 &deg, C, leaching time is 3 h 45 min and concentration of sulfuric acid is 40 wt.%. The results show that the purity of alumina reaches 79.28%, which is suitable for the production of aluminum metal. It is evident that this method of extraction of alumina from the kaolin ash is practical and feasible. The structural and morphological properties of the calcined microcrystalline powder was characterized by X-ray diffraction and scanning electron microscope (SEM).

Ordered mesoporous alumina with a large surface area was successfully synthesized in this work. Employing P123 as a structure-directing agent, the ordered mesostructure was fabricated only when the molar ratio of salicylic acid to citric acid was 2, and the large surface area was attributed to the addition of salicylic acid. The resulting alumina possesses a surface area of 520.65 m2 g−1 and a pore volume of 0.82 cm3 g−1. The surface area is still 300.20 m2 g−1 even after being calcinated at 800 °C.

The surface modification of γ -alumina nanoparticles by sebacic acid in super- and subcritical water was investigated. The modified alumina was characterised by Fourier-transform infrared spectra, X-ray diffraction patterns, transmission electron microscopy images, and thermogravimetric studies. The alumina nanoparticles were found to remain stable, and sebacic acid was bound to their surfaces at 200 ℃, but their crystallite structure was partially changed to that of boehmite above 200 ℃. Under supercritical conditions at 400 ℃, the alumina nanoparticles were totally changed to boehmite nanoparticles. The surface adsorption of sebacic acid is attributed to reactions between the surface -OH groups of alumina and the -COOH groups of sebacic acid. The modified alumina nanoparticles have -COOH groups on their surface, enabling hybridisation with various biomolecules, and thus allowing their application in several areas

In this paper, we report a procedure using soft/hard dual templates to produce γ-alumina with hierarchically ordered mesopores and macropores (HOMA). Polystyrene spheres colloidal crystals and block co-polymer are sequentially used as templates for ordered macropores and mesopores, respectively. Both macropores and mesopores are ordered pores. The wall of cage-like 500 nm macropores is composed of ordered mesopores of 3.6 nm, and the walls of mesopores are composed of γ-alumina. When loaded with Pt nanoparticles for CO oxidation, Pt/HOMA catalyst shows excellent catalytic properties.

The reaction of catalytic cyclisation of (+)-citronellal has been done using g-alumina and Zn/γ-alumina as catalysts. Zn/γ-alumina catalyst was prepared by impregnation of ZnBr2 into solid of γ-alumina in methanol as a solvent. The calcination process is performed on Muchalal reactor at 400 oC. The reactions were carried out under nitrogen gas atmosphere by mixing 5 mL sample and 1.0 g catalyst at 90-95 oC for 3 hours. The product of reaction was analyzed using GC, FT-IR and GC-MS. The reaction of cyclization of (+)-citronellal with γ-alumina catalyst did not give targeted product as well as reaction with Zn/g-alumina catalyst. Whereas, the reactions with Zn/γ-alumina catalyst gave four compounds of isopulegol stereoisomer. Conversion of (-)-Isopulegol, (+)-Neoisopulegol, (+)-Isoisopulegol and (+)-Neoisoisopulegol were 64,29%, 18,80%, 9,20% and 3,32% respectively. For that reason, the transformation of (+)-sitronelal using Zn/γ-alumina was considered to be the best catalyst. A reaction mechanism is proposed where the (+)-citronellal molecule binds to a catalyst Lewis acid site via the aldehyde oxygen and the π-electrons of the double bond. Subsequent protonation of the aldehyde via a neighbouring Bronsted acid site initiates the cyclisation to isopulegol. Keywords: catalytic cyclisation, impregnation, (+)-isopulegol

Hydrogenation of CO 2 to hydrocarbons is investigated over ceria-doped iron-based catalysts. While the addition of low levels of Ce leads to a marginal improvement in the catalyst's CO 2 hydrogenation ability, a decrease is observed when doping levels are raised to 10 wt.%. Even though the overall CO 2 conversion is only marginally, lower than with the undoped catalyst, the product distribution is shifted away from C 2 –C 5+ HC and towards CO. It was found that the addition of Ce leads to ceria particles being formed upon iron and thus most likely leading to a reduction in available chain-growth active sites on the iron.

Herein, mixed matrix membranes including alumina particles whose surfaces have been differently modified have been made and characterized. The polymeric matrix is a fluorinated polyimide, 6FDA-6FpDA, whereas the inorganic constituent parts are neat, silanized or poly-vinyl-pirrolidone-coated nanometric γ-Al 2 O 3 particles of 40 nm in diameter, which have been added in an approximated percentage of a 12% w/w. All the modified or unmodified added particles lead to similar improvements in the permselectivity of the gas pairs studied. Only in the case of the O 2 /N 2 pair the increase in selectivity for the silanized particles is not as effective as the observed permeability enhancement for the uncoated and PVP-coated particles. In case of CO 2 /CH 4 , the 1991 Robeson's upper bond line is overpassed. The characteristics of the permselectivity improvement for the different inorganic particles have been analyzed in terms of the properties of the particle–polymer interfacial properties.

The hydrolysis of chloropentafluoroethane (CFC-115) is investigated using alumina–zirconia catalysts prepared from boemite and γ-alumina composed of various different alumina contents. In the case of alumina–zirconia (alumina–zirconia(B)) catalysts prepared from boemite, a catalyst with an alumina content of 90 wt% exhibited the highest rate of hydrolysis. The acidity of these catalysts is found to correlate to the rate of hydrolysis, however, the hydrolysis rate increases linearly with an increase in acidity. On the other hand, in the case of alumina–zirconia (alumina–zirconia(A)) catalysts prepared from γ-alumina, the hydrolysis rate and acidity increase with an increase in alumina content. The hydrolysis rate increases linearly with an increase in acidity. The hydrolysis rate and acidity over alumina–zirconia(A) are removed from the hydrolysis rate and amount of acidity over alumina–zirconia(B), respectively. The residual hydrolysis rate increases linearly with the residual acidity. Thus, alumina–zirconia(B) catalysts have been determined to bear two types of acidity.

High loadings of nerve agent-related phosphonic acids adsorbed on γ-Al2O3 and concrete examined by 31P MAS NMR and high-field 27Al MAS NMR reveal the presence of several phosphonate−surface binding modes and greatly improved resolution of multiple AlIV sites. Some of the resolved AlIV sites are sensitive to surface hydroxylation/dehydroxylation are attributed to surface AlIV−OH groups (apparently having been observed for the first time). Although the number of surface AlIV sites detected by high-field 27Al MAS NMR (three) is in agreement with current surface models, their dehydroxylation behavior does not entirely concur with proposed dehydroxylation mechanisms. The various phosphonate−alumina surface species detected by 31P MAS NMR are consistent with those previously observed by IR techniques. In concrete, the formation of an aluminophosphonate species is directly observed, consistent with the recalcitrant extraction behavior exhibited by adsorbed phosphonates in environmental matrices.

Let's drink to that! Two alcohols (one primary and one secondary) can be coupled in an atom-efficient process by a hydrogen-autotransfer catalytic system in the form of silver subnanoclusters supported on gamma-Al(2)O(3). The recyclable heterogeneous catalyst promoted the one-pot C-C cross-coupling in the presence of a catalytic amount of the weak base Cs(2)CO(3) (see reaction mechanism).

Recently great efforts are being devoted to develop new methods of preparation of high-disperse Pd–CeO2 containing nanosystems stabilized on an oxide matrix. A new approach of synthesis consists in using the heterometallic PdII2CeIV2(μ-OOCMe)12(H2O)2 complex as a precursor to anchor Pd nanoparticles on the surface of γ-alumina in direct contact with CeO2. The present work is devoted to a structural study of this disperse Pd–CeO2 containing nanosystem after oxidative or reductive pretreatments in comparison with monometallic alumina-supported samples by XAFS and TEM. A strong interaction between Pd and ceria in the catalyst produced in the studied system affects reducibility of both PdO and CeO2, which in turn results in an increased low-temperature activity in CO oxidation along with a dramatic change of the ignition–extinction curve.

The sorption of U(VI) and phosphate on γ-alumina was investigated in binary (phosphate/γ-alumina; U(VI)/γ-alumina) and ternary (U(VI)/phosphate/γ-alumina) systems as functions of contact time, pH, ionic strength, solid-to-liquid ratio and U(VI) and/or phosphate concentrations by using a batch experimental method. It was found that the sorption of phosphate on γ-alumina increases with pH from 2.5 to 5.2 and then decreases with pH from 5.2 to 9.4. The sorption of phosphate on γ-alumina is insensitive to ionic strength. On the other hand, the sorption of U(VI) on γ-alumina increases with increasing pH over the range of 4–6. The sorption of U(VI) on γ-alumina increases slightly with decreasing ionic strength. In the ternary sorption system, it was found that the presence of phosphate increases the sorption of U(VI), whereas the presence of U(VI) has little effect on the sorption of phosphate. The sorption of U(VI) and phosphate in binary and ternary systems were interpreted in terms of surface complexation models. The effects of γ-alumina dissolution and CO 2 in the sorption systems were considered in modeling calculations. Four surface complexes of phosphate, XOHAlHPO 4 + , XH 2 PO 4 , XHPO 4 − and XPO 4 2− , and two surface complexes of U(VI), XOUO 2 + and XOUO 2 (OH) 2 − , were respectively used to reproduce the sorption of phosphate in phosphate/γ-alumina system and U(VI) sorption in U(VI)/γ-alumina system. The co-sorption of U(VI) and phosphate in the ternary sorption system was interpreted by a model which combines the surface complexation models for the binary sorption systems together in addition to considering the formation of a ternary surface complex, XOUO 2 HPO 4 − .

The synthesis of thiophene from the reaction of n-Butanol and carbon disulfide was performed in a fixed-bed reactor in the presence of promoted chromia on γ-alumina. A high selectivity to thiophene (87%) and a long lifetime of the catalyst (55 hour) was obtained at 450 °C with a 1: 6 n-Butanol to carbon disulfide molar ratio and LHSV 1 h−1 over γ-Al2O3 promoted by 7% K2CO3 with 15% Cr2O3 loaded. The catalytic behavior of these catalysts can be attributed to their dual-functional acidity and dehydrogenating and cyclized properties.

[Lepot, N.; Van Bael, M. K.; Van den Rul, H.; Mullens, J.] Hasselt Univ, Inst Mat Res Inorgan & Phys Chem, B-3590 Diepenbeek, Belgium. [Lepot, N.; Peeters, R.; Franco, D.] Univ Campus Diepenbeek, Verpakkingsctr, B-3590 Diepenbeek, Belgium. [D'Haen, J.] Hasselt Univ, Inst Mat Res, B-3590 Diepenbeek, Belgium. [Van Bael, M. K.; Van den Rul, H.; D'Haen, J.] Div IMOMEC, IMEC Vzw, B-3590 Diepenbeek, Belgium.

γ-Alumina surfaces pretreated at different temperatures (25 to 450 °C) and their rehydration after pyridine adsorption were studied using the conventional pyridine adsorption/DRIFTS technique. The results show that hydration at ambient temperature cannot convert all of the surface-coordinatived unsaturated Al sites to six-coordination, and weak and medium strong Lewis acid sites can still be observed for the fully hydrated γ-alumina. Dehydration at above 200 °C starts to generate strong Lewis acid sites. The number of weak, medium strong, and strong Lewis acid sites changes with dehydration temperature and all types of Lewis acid sites have adjacent OH groups. A good correlation between the number of Lewis acid sites and the intensity of perturbed OH groups is observed. Rehydration of the pyridine-adsorbed 450 °C pre-dehydrated alumina leads to removal of the pyridine adsorbed on the strong and medium strong Lewis acid sites and recovery of the surface of the original alumina. Water cannot replace the pyr...

A method of decomposing hexachlorobenzene (HCB) by gamma-alumina was investigated at low temperature of 300 degrees C. It was found that HCB was rather quickly decomposed under such a condition. Decomposition efficiency (DE) increases with increasing the surface area of gamma-alumina. Pretreated gamma-alumina has a better performance for the decomposition reaction. A high decomposition efficiency within the short reactive time of 60 min was achieved to be 94.2%, which was obtained by preheating gamma-alumina with the surface area of 220 m(2)g(-1) at 450 degrees C for 2 h. High surface area and appropriate pretreatment temperature probably provide more reactive sites such as the isolated OH groups and Al(3+) sites surrounded by O(2-) sites. These sites may induce the decomposition of HCB via a main ring-cracking process. The present study, hopefully, holds the promise for the eliminating of HCB contained hazardous materials in industrial application.

In the present investigation, γ-alumina nanoparticles with high specific surface area (351 m2/g) and relatively narrow pore size distribution was prepared using sol-gel method in the presence of aluminum isopropoxide as an aluminum precursor, distilled water, acetic acid as hydrolysis rate controller and tert-butanol as solvent. The calcined γ-alumina nanoparticles were characterized using X-ray diffractometer (XRD), scanning electron microscope (SEM) and nitrogen adsorption-desorption techniques. Prepared γ-alumina was tested for the adsorption of Pb2+ from aqueous solution at toxic metal concentrations, and isotherms were determined. The Pb2+ adsorption performance of the as-prepared samples was studied by atomic adsorption spectroscopy (AAS) method. According to the results, the prepared γ-aluminashowed the great adsorption performance of Pb2+with a high adsorption rate and adsorption capacity of 1150 mg/g when the adsorption reached to equilibrium for 5 min at room temperature and pH=5.5. The adsorbed amount increased rapidly with pH variation from pH 3 to 9. The optimum contact time, initial concentration of adsorbate, adsorbent mass and pH were determined and Langmuir, Freundlich and Tempkin adsorption models were obtained using metal ions concentrations in ranging from 100 to 400 mg/L. Correlation coefficients (R2) of Langmuir, Freundlich and Tempkin adsorption isotherms were 0.9994, 0.9975 and 0.9982, respectively, and Langmuir isotherm was more suitable for adsorption on γ-alumina than others. Also presence of Pb2+ ions has been confirmed by infrared spectroscopy. Efficient synthesis strategy, exceptionally high specific surface area and high adsorption efficiency of these mesoporous γ-alumina nanoparticles showed an excellent ability to remove Pb2+ heavy metal ions from aqueous solution that could find potential utility in the purification of polluted water.

In the present investigation, γ-alumina nanoparticles with high specific surface area (351 m2/g) and relatively narrow pore size distribution was prepared using sol-gel method in the presence of aluminum isopropoxide as an aluminum precursor, distilled water, acetic acid as hydrolysis rate controller and tert-butanol as solvent. The calcined γ-alumina nanoparticles were characterized using X-ray diffractometer (XRD), scanning electron microscope (SEM) and nitrogen adsorption-desorption techniques. Prepared γ-alumina was tested for the adsorption of Ni2+ from aqueous solution at toxic metal concentrations, and isotherms were determined. The Ni2+ adsorption performance of the as-prepared samples was studied by atomic adsorption spectroscopy (AAS) method. According to the results, the prepared γ-alumina showed the great adsorption performance of Ni2+ with a high adsorption rate and adsorption capacity of 350 mg/g when the adsorption reached to equilibrium for 3 min at room temperature and pH=5.5. The adsorbed amount increased rapidly with pH variation from pH 3 to 9. The optimum contact time, initial concentration of adsorbate, adsorbent mass and pH were determined and Langmuir, Freundlich and Tempkin adsorption models were obtained using metal ions concentrations in ranging from 30 to 90 mg/L. Correlation coefficients (R2) of Langmuir, Freundlich and Tempkin adsorption isotherms were 0.9961, 0.9831 and 0.9959, respectively, and Langmuir isotherm was more suitable for adsorption on γ-alumina than others. Also presence of Ni2+ ions has been confirmed by infrared spectroscopy. Efficient synthesis strategy, exceptionally high specific surface area and high adsorption efficiency of these mesoporous γ-alumina nanoparticles showed an excellent ability to remove Ni2+ heavy metal ions from aqueous solution that could find potential utility in the purification of polluted water.

The present work highlights for the first time that a thermal treatment of γ-Al2O3 in water at 80 °C for 24 h prior to Ag deposition (Ag/Al2O3-OH) leads to a drastic enhancement of H2-C3H6-SCR performance at low temperature. This enhancement is attributed to the higher NO x coverage on Ag/Al2O3-OH compared with that of Ag/Al2O3. The higher NO x adsorption capacity of the sample prepared from the γ-Al2O3 thermally-treated in water is proposed to result from the preferential interaction of Ag with newly-created Al2O3 anchoring sites (Al(OH)3 bayerite domains), which were not available on the untreated pristine support. Graphical Abstract

α-Al 2 O 3 platelets of various sizes and size distributions were synthesized from powder mixture of γ-Al 2 O 3 and Na 2 SO 4 flux by heating with and without microwaves under the same heating schedule. The average particle size of the sample obtained by heating the powder mixture without the use of microwaves was larger than that by heating the same powder mixture with the use of microwaves. In addition, the particle size distribution of the sample obtained with the use of microwaves was narrow compared to that obtained without the use of microwaves. It was indicated that microwave processing facilitates formation of smaller size of α-alumina platelets with narrower size distribution, due to the non-thermal effect in nucleation and growth of α-alumina.

A catalytic aspect, ‘surface catalytic NO reactions assisted by gas phase CO molecules’ on a Co2+-ensemble/γ-Al2O3 catalyst, was elucidated by successive density functional theory (DFT) calculations on a Co2+-dimer/γ-Al2O3 model surface. Unique cis-(NO)2 dimeric species formed due to a specific alignment of the unoccupied orbitals on the Co2+-dimer, whose vibrational frequencies were almost identical to those for conventional gem-dinitrosyl species. The cis-(NO)2 species showed much higher reactivity with CO than the gem-dinitrosyl species, through the 2π∗–2π∗ bonding between the two NO adsorbates. Detailed DFT calculations for the reaction pathways indicated an Eley–Rideal mechanism with an unusually large reactive cross-section.

NO x reduction with a combination of catalysts, Pd catalyst, NO x storage reduction (NSR) catalyst and Cu/ZSM-5 in turn, was investigated to elucidate for the high NO x reduction activity of this catalyst combination under oxidative atmosphere with periodic deep rich operation. The catalytic activity was evaluated using the simulated exhaust gases with periodically fluctuation between oxidative and reductive atmospheres, and it was found that the NO x reduction activity with this catalyst combination was apparently higher than that of the solely accumulation of these individual activities, which was caused by the additional synergic effect by this combination. The Pd catalyst upstream of the NSR catalyst improved NO x storage ability by NO2 formation under oxidative atmosphere. The stored NO x was reduced to NH3 on the NSR catalyst, and the generated NH3 was adsorbed on Cu/ZSM-5 downstream of the NSR catalyst under the reductive atmosphere, and subsequently reacted with NO x on the Cu/ZSM-5 under the oxidative atmosphere.

An electrochemical cell was formed by enclosing a commercial catalyst containing cupric chloride supported by γ-alumina between electrodes of copper and iron. The voltage obtained is a logarithmic function of the vapour pressure of the water sorbed by the support. Voltages of a few hundred millivolts are obtained at relative pressures between 0.1 and 0.8 and temperatures between 25 and 170°C.

［35S］DBT水素化脱硫反応の結果に基づき，高表面積TiO2担持およびγ-Al2O3担持MoS2，CoMoS，NiMoS水素化脱硫触媒の反応特性を比較した。すでに我々が公表したMoS2およびCoMoS系触媒を用いて得た結果のまとめと，NiMoS系触媒を用いた際の新結果との比較を行った。 MoS2/Al2O3触媒にNiあるいはCoを添加すると，水素化脱硫反応が著しく促進する。プロモーターがどちらであっても，移動可能な硫黄量（S0）の増加が見られる。しかし，相異点もあり，Ni助触媒を添加したMoS2触媒では，H2Sの放出速度定数（kRE）がNi : Mo比に対して火山形プロットになるのに対し，Co助触媒においては，同定数は低いCo : Mo比から横ばいになることが分かった。 脱硫反応時にMo/TiO2触媒上に形成されるTiMoS相が硫黄の挙動を促進させるために，Mo/Al2O3触媒に比べMo/TiO2触媒の活性が高い。しかし，CoMo/TiO2触媒はCoMo/Al2O3触媒より活性が低い。その理由として考えられることは二つあり，（1）TiMoS相とCo助触媒の影響が同時に発生し，硫黄 ・ 金属間の結合が不安定となるためと，（2）MoとCo間の相互作用が十分に起こらないためである。また，Mo/TiO2触媒にNi助触媒を添加すると，kREおよびS0の値がともに増加することも分かった。この結果，TiO2担持NiMo触媒とAl2O3担持NiMo触媒の脱硫能が近づいた。 35Sアイソトープトレーサー法により，水素化脱硫触媒の反応特性に及ぼすCoの添加効果とNiの添加効果は異なっていることが明らかとなった。

Insights of the chemical mechanism for the hydrothermal synthesis of nanostructured alumina are elucidated for the first time, demonstrating the effect of the NaOH : Al molar ratio not only on the resulting morphology of the material but also on the product yield. Highly uniform pure g-Al2O3 nanorods are synthesised under acidic conditions (pH < 4), while basic medium (pH > 9) lead to g-Al2O3 nanoplates. Maximisation of the morphological purity leads to a decrease in the overall aluminium yield which can be overcome by successful reusability of the synthesis medium in an effort to increase efficiency (yield and productivity) and minimise waste production towards feasible large-scale manufacturing of nanostructured materials.

International audience; Controlling the nature and size of cobalt(II) polynuclear precursors on γ-alumina and silica-alumina supports represent a challenging question for the synthesis of optimally active cobalt based heterogeneous catalysts. By density functional theory (DFT) calculations, we reveal how after drying the interaction of cobalt(II)precursor on γ-alumina is driven by a structural recognition phenomenon leading to the formation of an epitaxial Co(OH)2 precipitate involving a Co-Al hydrotalcite-like interface. On silicaalumina surface, this phenomenon is prevented due to thepassivation effect of silica domains. This finding opens new routes to tune the metal-support interaction at the synthesis step of heterogeneous catalysts.

The irreversible adsorption of boron trifluoride on calcined γ-alumina and amorphous chromia, in both cases at room temperature, has been studied using [ 18 F]-labelled BF 3 . Although the resulting γ-alumina surface has some catalytic activity for the room temperature fluorination by anhydrous HF of CH 3 CCl 3 under static conditions, its activity is far lower than that of γ-alumina, which has been fluorinated with SF 4 , nominally at room temperature. A possible explanation for the observed behaviour is given.

The relationship between particle size and catalytic activity of gold nanoparticle catalysts with γ-Al2O3 as support has been investigated. The catalysts were prepared via the gold sol with different particle sizes by micelle method, and their structures were characterized by HRTEM and XRD, respectively. Furthermore, the catalytic activities were tested by CO oxidation. Experimental results showed that the catalytic activity became much weaker when gold particles were increased from 3.2 to 6.6 nm. Additionally, the particle size was also a key factor to govern catalytic activity with regard to gold supported on TiO2 prepared by the methods of deposition-precipitation.

Sol–gel-prepared mesoporous alumina (SG-Al 2 O 3 ) was found to act as a potential catalyst for the complete dechlorination of carbon tetrachloride at temperatures ⩾350 °C in the presence of water. The main products were CO 2 and HCl at 400 °C and the deactivation of the catalyst by chlorination was inhibited. In the absence of water, however, lower reactivity was observed and the undesired AlCl 3 , COCl 2 , and Cl 2 by-products formed. The % conversion and the products profile were temperature dependent where higher % conversion and less COCl 2 , AlCl 3 and Cl 2 were observed at higher temperatures.

The knowledge of the properties of gamma-alumina is of great importance in order to control its surface for numerous applications. We investigate the kinetic behavior of the hydrated alumina (110) surface toward water desorption: the minimum energy path is presented for successive desorption steps starting from the completely hydrated surface toward the dehydrated one. It appears that water desorption is a non activated process. A kinetic model is proposed based on an extension of the Eyring theory. This model is a useful tool to understand the evolution of water coverage during the pretreatment of alumina. It is then used to model temperature programmed desorption experiments for various heating rates. The shape of the desorption curve is qualitatively reproduced, and the differences between theory and experiments are discussed.

The influence of Ce0.68Zr0.32O2 solid solution on properties of γ-alumina based washcoat on FeCrAl foils was investigated. FeCrAl foils were pretreated at 950°C in air for 10 h before coating washcoat. Different amounts of Ce0.68Zr0.32O2 solid solution were added into a-alumina-based slurries. The properties of washcoats were measured by ultrasonic vibration and thermal shock test, SEM, BET and XRD. The results show that the addition of Ce0.68Zr0.32O2 solid solution into slurries can improve γ-Al2O3-based washcoat adhesion on FeCrAl foils. The more the Ce0.68Zr0.32O2 solid solution added into slurries, the higher was the specific surface area of aged samples. XRD characterization proved that ceria-zirconia solid solution can inhibit the transformation of γ-A12O3 crystal into others at 1050°C for 20 h.

The interaction of Co6 cluster with partially dehydroxylated γ-alumina surface was studied by the DFT method. Hydrogen atoms of surface hydroxyl groups can be transferred to the metal particle to form partially oxidized cobalt states. The energy characteristics of hydrogen transfer were determined and changes in the electronic structure of supported Co6 particles were characterized.

비정질알루미나와 기공형성제에 물을 혼합하여 원통형으로 성형하고 수화한 다음, 건조 및 소성하여 직경 5 mm, 평균 길이 약 10 mm의 γ-알루미나 펠릿을 제조하였다. 이를 Fe(NO₃)₃ㆍ9H₂O 용액과 CH₃COOH 혼합용액에 침척시켜 200℃ 온도로 3시간 수열처리한 후, 건조하고 소성하여 촉매를 제조하였다. 이와 같이 수열법에 의해 제조된 Fe₂O₃/γ-Al₂O₃ 세라믹촉매를 환경촉매로 적용하기 위해, 아닐린과 같은 난분해성물질을 촉매를 사용하지 않는 오존단독공정과 촉매를 사용하는 촉매오존(catalytic ozonation)공정으로 구분하여 OH 라디칼 전환반응 개시제로서의 기능과 그 분해특성을 비교하였다.

A simple method for preparing Al 2 O 3 monoliths with hierarchical pore structure, using dextran gel beads as template, is presented. Removal of the template resulted in spherical macroporous cavities interconnected by macropores. Mesopores with diameter around 19 nm were also present in the alumina framework. The materials have high pore volumes with significant fractions of macropores. This can facilitate the use of this type of monoliths within flow-through microreactor systems.

A method is introduced to prepare almost-spherical submicrometer-sized α-alumina via surface modification of γ-alumina with an alumina sol. Milled γ-alumina, in the presence of 3 wt% of α-alumina with a median particle size (d50) of 0.32 μm (AKP-30), produced irregularly shaped α-alumina with d50∼0.3 μm after heat treatment at 1100°C for 1 h. γ-alumina that had been surface-modified by milling in the presence of 3 wt% of the alumina sol resulted in almost-monosized, spherical α-alumina ∼0.3 μm in size after heat treatment at 1100°C for 1 h. Furthermore, almost-spherical α-alumina 0.1—0.2 μm in size was obtained by milling γ-alumina with 3 wt% of AKP-30 alumina in the presence of 3 wt% of the alumina sol, followed by heat treatment at 1100°C for 1 h. The alumina sol that has been introduced in this work seems to act as a dispersant, in addition to helping to form a spherical shape.

폐 염화알루미늄(AlCl₃) 수용액과 수산화나트륨(NaOH) 용액의 가수분해 반응에 의해 무정형의 수산화알루미늄 겔을 석출시키고, 이를 숙성하여 다공성 유사베마이트(pseudo-boehmite) 겔을 제조하였다. pH를 7.6~11.6 범위로 조절하고 반응온도를 60~100℃로 변화시켜 2~24시간 숙성시켰을 때, 겔 침전물의 결정변화, 적외선흡수스펙트럼의 변화, 비표면적 및 기공구조의 변화를 조사하여 최대 기공부피를 갖는 유사베마이트 겔의 제조조건을 확립하였다. pH 7.6~9.6 범위에서 석출된 겔 침전물로부터 250~357 ㎡/g 정도의 비표면적과 0.4~0.74 cc/g 의 기공부피 그리고 58~114 Å의 평균기공크기를 갖는 다공성 유사베마이트가 제조되었으며, pH 10.6~11.6 범위에서 석출된 겔 침전물로부터는 기공이 거의 없는 베이어라이트(bayerite)가 제조되었다.

Variations in the structure of gamma-alumina (γ-Al2O3), derived from well-crystalline boehmite, calcined at various temperatures in air were investigated. Consistent distribution of cation coordina...

We herein report on the PW-DFT study of molybdenum disulfide catalyst supported on γ-alumina. An Mo 4 S 8 sheet, in a complete periodical environment, was docked to three surfaces of alumina. We found that the alumina surface controlled the orientation and the morphology of MoS 2 sheets. The results show that for all alumina surfaces the Mo-edge- and Mo-S-edge-adsorbed MoS 2 sheets are the most stable configurations.