Surface reactions of dimethyl ether on γ-Al2O3

The surface reactions of dimethyl ether (DME) on industrial alumina (γ-Al₂O₃) were studied by chromatographic analysis of the products at the outlet of the flow reactor and (independently) by diffuse reflectance IR spectroscopy. The major products of the reactions at 250°С were found to be methanol formed in the reaction of DME with hydroxyl groups (the 3720 and 3674 cm^–1 bands in the diffuse reflectance spectrum) and various methoxy groups (the 1121, 1070, 695, and 670 cm^–1 bands in the differential spectra). The presence of molecularly adsorbed methanol was confirmed by experiments with methanol fed in a high-temperature IR cell. The interaction of the resulting methanol molecule with the hydroxyl group led to the formation of a water molecule in the gas phase and a methoxy group on the oxide surface. Strong adsorption of molecular DME was revealed, which was favored by an increase in the temperature of the preliminary calcination of oxide from 250 to 450–500°С; treatment of alumina with water vapor after its preliminary contact with DME led to a recovery of the hydroxyl coating and a replacement of molecularly adsorbed DME with hydroxyl. The thermal effect recorded in a flow reactor was positive during the adsorption of DME and negative during the desorption of weakly bonded DME. Schemes of formation of methoxy groups in the interaction of DME and methanol with surface hydroxyls were suggested.     

The Process of Acetonitrile Synthesis over γ-Al2O3 Promoted by Phosphoric Acid Catalysts

The influence of principal parameters (reaction temperature, ratio of acetic acid and ammonia, composition of reactionary mixture and promotion of catalysts) on the selectivity and yield of the desired product was studied in the reaction of catalytic acetonitrile synthesis by ammonolysis of acetic acid. The processing of γ-Al₂O₃ by phosphoric acid increases amount of the centers, on which carries out reaction of acetamide dehydration. The kinetic model of a limiting stage of reaction – the acetamide dehydration to acetonitrile was suggested. In the process of ammonolysis of acetic acid it was demonstrated that the use of catalysts promoted by phosphoric acid and ratio NH₃:CH₃COOH=(3-4):1 at temperatures of a reactor 360-390°С leads to the increase of acetonitrile productivity to 0.7-0.8 g/cm³·h and allows to minimize formation of by-products.     

TG Study of the Dispersion Threshold of Mn2O3 on γ-Al2O3

Mn₂O₃/-Al₂O₃ catalysts were prepared by the impregnation method, and the maximum monolayer dispersion capacity or dispersion threshold value of Mn₂O₃ on the surface of -Al₂O₃ was determined to be 13.08% from the decomposition mass loss of supported Mn(NO₃)₂ in the monolayer state. This was compared with the values estimated from a close-packed monolayer model and an interaction model. It was confirmed that the high activities and selectivities of the catalysts for benzoic acid hydrogenation to benzaldehyde are due to the monolayer dispersion of the Mn₂O₃ on the surface of -Al₂O₃.This revised version was published online in November 2005 with corrections to the Cover Date.     

Adsorption of Chlorobenzene on γ-Al2O3 Obtained by Calcination of Boehmite at Various Temperatures

The influence exerted by the temperature of boehmite calcination in air within the range 450-600°C on the adsorption properties of the resulting -Al₂O₃ with respect to chlorobenzene was studied.     

Adsorption of chlorobenzene and benzene on γ-Al2O3/atl>

Adsorption of chlorobenzene and benzene on -Al₂O₃ was investigated in the 413--572 K temperature region at an adsorbate partial pressure ranging from 2 to 1000 Pa. The adsorption isotherms were measured and the isosteric heats and the entropy characteristics of adsorption were determined. The experimentally found and theoretically calculated entropy changes upon adsorption were compared. The mobility of the molecules of both adsorbates in the adsorption layer was limited with respect to that predicted by the ideal two-dimensional gas model. The mechanism of adsorption of benzene and chlorobenzene is discussed.     

Elucidating the structure of surface acid sites on γ-Al2O3

Differential pair distribution function analysis was applied to resolve, with crystallographic detail, the structure of catalytic sites on the surface of nanoscale γ-Al(2)O(3). The structure was determined for a basic probe molecule, monomethylamine (MMA), bound at the minority Lewis acid sites. These active sites were found to be five-coordinate, forming distorted octahedra upon MMA binding. This approach could be applied to study the interaction of molecules at surfaces in dye-sensitized solar cells, nanoparticles, sensors, materials for waste remediation, and catalysts.     

Environment-friendly synthesis of N-phenylpiperidine from aniline and 1,5-pentanediol over γ-Al2O3 catalyst

An efficient environment-friendly synthesis of N-phenylpiperidine was developed from aniline and 1,5-pentanediol over γ-Al2O3 catalyst under atmospheric pressure. The conversion of 1,5-pentanediol reached 97% and the selectivity for N-phenylpiperidine attained 94%. The structure of the catalyst was characterized by NH3-TPD and BET. The influences of calcination temperature of the catalyst and reaction temperature on activity and selectivity of the catalyst were investigated.     

Environment-friendly synthesis of N-phenylpiperidine from aniline and 1,5-pentanediol over γ-Al2O3 catalyst

An efficient environment-friendly synthesis of N-phenylpiperidine was developed from aniline and 1,5-pentanediol over γ-Al2O3 catalyst under atmospheric pressure. The conversion of 1,5-pentanediol reached 97% and the selectivity for N-phenylpiperidine attained 94%. The structure of the catalyst was characterized by NH3-TPD and BET. The influences of calcination temperature of the catalyst and reaction temperature on activity and selectivity of the catalyst were investigated.     

γ-Al2O3改性对AlCl3/γ-Al2O3催化剂性能的影响

采用HCl和NaOH改性γ-Al2O3载体制备AlCl3/γ-Al2O3固载催化剂,用吡啶-FTIR和吡啶-TPD技术分析了催化剂的表面酸性(酸中心类型、酸强度和酸量),并以1-癸烯齐聚作为探针反应,研究了催化剂的稳定性以及催化剂对聚合反应的影响.结果表明,催化剂含有两种酸类型,即Lewis酸和Br(o)nsted酸,与未改性的催化剂相比,氢氧化钠改性载体制备的催化剂,酸量增大了47％,催化剂催化1-癸烯的齐聚反应活性增加了11.4％;而经盐酸改性制备的催化剂酸量增大112％,催化剂的活性增加了33.6％.酸强度依AlCl3/γ-Al2O3,AlCl3/γ-Al2O3(NaOH),AlCl3/γ-Al2O3 (HCl)的顺序增强.     

Effect of the Morphology of γ-Al2O3 Nanosized Particles on Their Adsorption Properties

Russian Journal of Physical Chemistry A - γ-Al2O3 porous nanostructures with different morphologies are prepared from an aluminitride nanopowder (obtained by electric explosion) by treatment...     

Acid–Base Properties of γ-Al2O3 Suspension Studied by pK Spectroscopy

Theoretic fundamentals of the method of pK spectroscopy are formulated as applied to investigating acid–base properties of suspensions, hydrosols, and solutions of macromolecules. The computer-aided treatment of the data of potentiometric titration of the relevant substrates makes it possible to determine the molar fractions of corresponding acid–base groups (per total number of these groups) as a function of pK values of these groups. An appropriate computer program is tested with a model example and resulted in a pK spectrum meeting the model requirements. The method of pK spectroscopy is used to study acid–base properties of -Al₂O₃ suspension. In the pK spectrum obtained, four bands corresponding to four types of acid–base groups on the oxide surface are observed that appears to be a direct verification of the James–Parks model.     

A Study of Water Interaction with γ-Al2O3Surface by Adsorption Calorimetry

The steps at 70, 62, and 56 kJ/mol were specified on the dependences of differential heats of adsorption on the values of adsorption aon the hydroxylated -Al₂O₃surface resulted from the interaction of adsorbed water molecules with the surface-coordinated water molecules, acid and basic hydroxyl groups, respectively; effective charges qwere estimated for the protons of coordinated water molecules and acid and basic OH groups. The hydration numbers were calculated in the region of monolayer coverage for the three aforementioned adsorption sites. The texture changes discovered in -Al₂O₃particles were attributed to the interlamellar swelling of the secondary sorbent packets formed from its primary particles.     

Preparation of Nano-Sized γ-Al2O3 Supported Iron Catalyst for Fischer-Tropsch Synthesis by Solvated Metal Atom Impregnation Methods

Two types of small iron clusters supported onγ-Al2O3-RT(dehydroxylated at room temperature) andγ-Al2O3-800 (dehydroxylated at 800℃) were prepared by solvated metal atom impregnation (SMAI) techniques. The iron atom precursor complex, bis(toluene)iron(0) formed in the metal atom reactor, was impregnated intoγ-Al2O3 having different concentrations of surface hydroxyl groups to study the effect of surface hydroxylation on the crucial stage of iron cluster formation. Catalysts prepared in this way were characterized by TEM, Mossbauer, and chemisorption measurements, and the results show that higher concentration of surface hydroxyl groups ofγ-Al2O3-RT favors the formation of more positively charged supported iron cluster Fen/γ-Al2O3-RT, and the lower concentration of surface hydroxyl groups ofγ-Al2O3-800 favors the formation of basically neutral supported iron cluster Fen/γ-Al2O3-800. The measured results also indicate that the higher concentration of surface hydroxyl groups causes the rapid decomposition of precursor complex, bis(toluene)iron(0), and favors the formation of relatively large iron cluster. Consequently, these two types of catalysts show different catalytic properties in Fischer-Tropsch reaction. The catalytic pattern of Fen/γ-Al2O3-RT in F-T reaction is similar to that of the unreducedα-Fe2O3 and that of Fen/γ-Al2O3-800 is similar to that of the reducedα-Fe2O3.     

Effective Removal of CF4 by Combining Nonthermal Plasma with γ-Al2O3

Conversion of CF₄ was experimentally evaluated with three systems including catalytic hydrolysis, NTP-alone and plasma catalysis. Firstly, activity of γ-Al₂O₃ for CF₄ conversion was tested via catalytic hydrolysis. Experimental results indicate that the highest CF₄ conversion (72%) could be achieved with γ-Al₂O₃ in the presence of 45% H₂O_(g) with the operating temperature of 900 °C and the apparent activation energy is calculated as 85 kJ/mol using power rate law model. For plasma-based systems, results indicate that CF₄ conversions achieved with plasma catalysis remain 100% with the applied voltage ranging from 12 to 23 kV, while the highest CF₄ conversion achieved with NTP-alone is 86%. For the effects of various parameters on plasma-based systems, the results indicate that plasma catalysis also has better resistivity for higher total flow rate, CF₄ concentration and O₂ contents. Especially, CF₄ conversion could maintain at 100% with the operating applied of 23 kV as CF₄ concentration is increased to 10,000 ppm. On the other hand, CF₄ conversion achieved with NTP-alone is 18% at the same conditions. In addition, negative effect of O₂ on plasma catalysis could be reduced by the addition of Ar due to its good discharge properties and high excitation threshold energy (13 eV). The kinetics of plasma catalysis is investigated for CF₄ conversion by a simplified model, and the results indicate that overall energy constant achieved with plasma catalysis reaches 0.015 mg J^?1. Overall, plasma catalysis is demonstrated with good potential for the reduction of CF₄ emission.

     

Ammonia Decomposition over Bimetallic Nitrides Supported on γ-Al2O3

A series of monometallic nitrides and bimetallic nit-rides were prepared by temperature-programmed reaction with NH3. The effects of Co, Ni and Fe additives and the synergic action between Fe, Co, Ni and Mo on the ammonia decomposition activity were investigated. TPR-MS, XRD were also carded out to obtain better insight into the structure of the bimetallic nitride. The results of ammonia decomposition activity show that bimetallic nitrides are more active than monometallic nitrides or bimetallic oxides.     

Synthesis of 2,2,4-trimethyl-1,2-dihydroquinolines over metal-modified 12-tungstophosphoric acid-supported γ-Al2O3 catalyst

Research on Chemical Intermediates - In spite of having significant pharmacological importance, scalable synthesis of 2,2,4-trimethyl-1,2-H-dihydroquinoline (TMQ) is always being cumbersome due to...     

Chemical Modification of γ-Al2O3 Surface with Aryl Silanes

The effect of main factors (the nature and functionality of a modifier, the presence of water) on the chemical modification of -Al₂O₃ surface with aryl silanes was studied by an FTIR spectroscopy and elemental analysis.