KF promoted mesoporous γ-Al2O3 with strong basicity: Preparation,characterization and catalytic activitiy for transesterification to biodiesel

The present paper describes the preparation of KF/M-γ-Al₂O₃, efficient mesoporous solid bases. The procedure involves loading KF into a crystalline mesoporous γ-Al₂O₃ that was synthesized by the self-assembly of poly-4-vinylpyridine (P4VP) with Al³⁺ species. The synthesis is based on the strong acid-base interaction, hydrothermal treatment at 180°C and calcination at 550°C. Characterizations using XRD analysis and low temperature N₂ adsorption indicated that different amounts of KF could be introduced into crystalline mesoporous γ-Al₂O₃ to obtain catalysts with high BET surface areas, large pore volumes and uniform pore size distribution. Based on SEM images, KF/M-γ-Al₂O₃ catalysts have rough surface character and a large nanopore volume. CO₂-TPD curves registered for KF/M-γ-Al₂O₃ contain high temperature peaks, indicating strong basicity of the catalysts. Under the same reaction conditions KF/M-γ-Al₂O₃ catalysts exhibit much better activities for transesterification to biodiesel than KOH, NaOH, H₂SO₄, hydrotalcite and CaO. Enhanced activities appear to arise from strong basisity and large BET surface areas.     

Catalytic dehydrogenation of cyclohexene over MoO<Subscript>3</Subscript>/γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts

A series of MoO₃/γ-Al₂O₃ catalysts with different Mo surface densities (Mo atoms/nm²) has been prepared by incipient wetness impregnation method. Structural characteristics of the prepared catalysts were investigated by atomic absorption spectroscopy, X-ray diffraction, Fourier Transform Infrared spectroscopy, N₂ adsorption at −196 °C, and temperature-programmed reduction (TPR). The catalytic activities of the prepared catalysts were tested by cyclohexene conversion between 200 and 400 °C. XRD results indicated that molybdenum oxide species were dispersed as a monolayer on the support up to 4.04 Mo atoms/nm², and the formation of crystalline MoO₃ was observed above this loading. FTIR and TPR results showed that molybdenum oxide species were present predominantly in tetrahedral form at lower loading, and polymeric octahedral forms were dominant at higher loading. Cyclohexene conversion reaction proceeded mainly through the simple dehydrogenation pathway in the studied temperature range 200–400 °C and was found to be highly dependent on MoO₃ dispersion.     

Synthesis of high surface area transitional alumina from Al(OPh)<Subscript>3</Subscript>

Al(OPh)₃ involving sterically hindered phenyl groups on ultrasonic assisted micro hydrolysis yielded a mixture of boehmite and bayerite as deduced from the FTIR and powder X-ray diffraction pattern. In the thermogravimetric trace, the complete removal of decomposable moieties of the hydrolyzed gel occurred around 530 °C. Calcining the gel at temperatures 600, 700, 800 and 900 °C showed crystalline tetragonal δ-Al₂O₃ to be the product at 900 °C as deduced from FTIR, ²⁷Al NMR and PXRD techniques. δ-Al₂O₃ showed a surface area of 135 m²/g with rectangular bar like morphology with the sizes below 50 nm in the TEM images.     

Biomolecule-Assisted Synthesis of Hierarchical Multilayered Boehmite and Alumina Nanosheets for Enhanced Molybdenum Adsorption

The effective utilization of various biomolecules for creating a series of mesoporous boehmite (γ-AlOOH) and gamma-alumina (γ-Al₂O₃) nanosheets with unique hierarchical multilayered structures is demonstrated. The nature and concentration of the biomolecules strongly influence the degree of the crystallinity, the morphology, and the textural properties of the resulting γ-AlOOH and γ-Al₂O₃ nanosheets, allowing for easy tuning. The hierarchical γ-AlOOH and γ-Al₂O₃ multilayered nanosheets synthesized by using biomolecules exhibit enhanced crystallinity, improved particle separation, and well-defined multilayered structures compared to those obtained without biomolecules. More impressively, these γ-AlOOH and γ-Al₂O₃ nanosheets possess high surface areas up to 425 and 371 m² g⁻¹, respectively, due to their mesoporous nature and hierarchical multilayered structure. When employed for molybdenum adsorption toward medical radioisotope production, the hierarchical γ-Al₂O₃ multilayered nanosheets exhibit Mo adsorption capacities of 33.1–40.8 mg g⁻¹. The Mo adsorption performance of these materials is influenced by the synergistic combination of the crystallinity, the surface area, and the pore volume. It is expected that the proposed biomolecule-assisted strategy may be expanded for the creation of other 3D mesoporous oxides in the future.     

A theoretical and experimental XAS study of monolayer dispersive supported CuO/γ-Al2O3 catalysts

The local structures of supported CuO/γ-Al₂O₃ monolayer dispersive catalysts with different CuO loadings have been investigated by EXAFS and multiple scattering XANES simulations. The EXAFS results show that the first nearest neighbors around the Cu atoms in the CuO/γ-Al₂O₃ catalysts are similar to that of the polycrystalline CuO powder, which is independent of the CuO loadings. Moreover, the Cu K-XANES FEFF8 calculations for CuO reveal that the monolayer-dispersed CuO species are of small distorted (CuO₄)_mⁿ⁺ clusters, which is mainly composed of a distorted CuO₆ octahedron incorporated in the surface octahedral vacant sites of the γ-Al₂O₃ support. We consider that the CuO species for the CuO/γ-Al₂O₃ catalysts with loadings of 0.4 and 0.8 mmol/100 m² are distorted (CuO₄)_mⁿ⁺ clusters composed mainly of a distorted CuO₆ octahedron incorporated in the surface octahedral vacant sites of the γ-Al₂O₃ support after calcinations at high temperature in air for a few hours. On the contrary, for the CuO/γ-Al₂O₃ with loading of 1.2 mmol/100 m², the local structure of Cu atoms in CuO/γ-Al₂O₃ is similar to that of polycrystalline CuO powder.     

Highly effective water adsorbents based on aluminum oxide

A method of preparation of a stable, high performance water adsorbent with the phase composition η-Al₂O₃ + γ-Al₂O₃ + χ-Al₂O₃ from thermally activated hydrargillite has been developed. The synthesis procedure does not involve a reprecipitation stage. The resulting adsorbent has a high specific surface area (400 m²/g) and a mean pore diameter of 3.5 nm or below. The static capacity of the adsorbent reaches 24.2 g H₂O per 100 g of sorbent, and its dynamic capacity is 8.2 g H₂O per 100 g of sorbent. Service life tests showed the stability of the adsorbent in multiple sorption-desorption cycles. The minimum dew point in drying is ?58.8°C.     

Zur Konstitution von Ba2WO3F4 und Ba2MoO3F4

On the Structure of Ba₂Wo₃F₄ and Ba₂MoO₃F₄ Ba₂[WO_2/2O₂F₂]F₂ has been prepared for the first time as colourless single crystals (from powder, Au-tube, 680°C, 90 d). It crystallizes in the monoclinic (C c) crystal system with a = 1151.1, b = 938.2, c = 718.8 pm, ß = 126.17°, Z = 4. d_x = 6.17, d_pyk = 6.13 g · cm^?3. (Fourcirclediffractometer PW 1100, Fa. Philips, MoKα-, ω-2Θ-scan, 1832 I₀(hkl) R = 8.3, R_w = 7.4%). Parameters see in the text. The isotypic Ba₂MoO₃F₄ has been prepared as powder (a = 1147.5, b = 937.0, c = 725.1 pm, ß = 126.42°). The structure shows chains of (WO_2/2O₂F₂) groups along [001]. To establish O^2? and F^? on the positions IR and Raman Spectra are employed. The Madelung Part of Lattice Energy, MAPLE, is calculated and discussed.     

炭载钌催化剂的微波制备及其水相乙酰丙酸加氢性能

生物质衍生物乙酰丙酸是生物质转化过程中重要的平台分子,对其进行催化加氢可以得到高附加值的产物,是连接生物质转化和石油化工的重要途径。本实验研究了无溶剂微波辅助热解法绿色制备负载型钌基催化剂,以Ru₃（CO）₁₂为金属前体,碳纳米管、椰壳活性炭和活性氧化铝为催化剂载体,该制备方法简单易操作,环保高效低能耗,不使用溶剂,避免了杂质的引入和对催化剂的污染,是一种新型负载型贵金属催化剂的制备方法。同样采取传统浸渍法制备Ru/γ-Al₂O₃-IM。在乙酰丙酸水相催化加氢反应中的催化活性顺序为Ru/AC > Ru/CNT ≈ Ru/FCNT > Ru/γ-Al₂O₃-MW ≈ Ru/γ-Al₂O₃-IM。比较不同反应溶液水、甲醇、乙醇、苯甲醚、环己烷和丙酮等对于乙酰丙酸催化加氢反应的影响,并通过考察反应温度、反应压力和反应物初始浓度等因素对加氢反应的影响,确定最佳实验条件为：反应温度为90℃,反应压力2.0 MPa,适宜反应物浓度为0.10 g/mL,产品GVL收率大于99%。     

Aluminum oxide and systems based on it: Properties and applications

The metastable forms of aluminum oxide that exist in the range of 300–800°C are characterized; differences in the microstructures of homogeneous γ-, η-, and χ-Al₂O₃ are demonstrated; and the acid-base properties of the above modifications are compared. The catalytic properties of aluminum oxide in ethanol dehydration and propionitrile ammonolysis were studied. It was found that an increased surface concentration of Lewis acid sites, including strong acid sites (ν(CO) = 2237 cm^?1), is required for preparing an effective catalyst for the dehydration of ethanol, whereas the rate of propionitrile conversion increased proportionally to the surface concentration of Brønsted acid sites. γ-Aluminum oxide was used to prepare catalysts for carbon monoxide oxidation. It was found that the supporting of Pd on γ-Al₂O₃ did not change the support structure. Palladium on the surface of γ-Al₂O₃-550 (T _calcin = 550°C, S _BET = 300 m²/g) occurred as single particles (2–3 nm) and aggregates (～100 nm). The single particles were almost completely covered with a layer of aluminum oxide to form core-shell structures. According to XPS data, they were in atypical states (BE(Pd 3d _5/2) = 336.0 and 338.0 eV), which were not reduced by hydrogen in the range of 15–450°C and were resistant to the action of the reaction mixture. Palladium on the surface of γ-Al₂O₃-800 (S _BET = 160 m²/g) was in the states Pd⁰ and PdO, which are typical of Pd/Al₂O₃, and the proportions of these states can change under the action of the reaction mixture. An increase in the T _calcin of the Pd/Al₂O₃(800)-450 catalyst from 450 to 800 → 1000 → 1200°C led to the agglomeration of palladium particles and to an increase in the temperature of 50% CO conversion from 145 to 152 → 169 → 189°C, respectively. α-Aluminum oxide was used in the preparation of an effective Mn-Bi-O/α-Al₂O₃ supported catalyst for the synthesis of nitrous oxide by the oxidation of ammonia with oxygen: the NH₃ conversion was 95–97% at 84.4% N₂O selectivity.     

The formation mechanism and distribution of micro-aluminum oxide layer

It is of great significance to study the thermal oxidation process to understand the reaction mechanism of aluminum particle and further its applications in propellants. The physical and chemical properties of micron-aluminum particle were evaluated by scanning electron microscopy, laser particle size analyzer, X-ray diffractometer and inductively coupled plasma atomic emission spectrometer. The thermal oxidation characteristics of the sample were studied by thermal analyzer. The experimental results showed that the initial oxide thickness of the sample was about 3.96 nm, and the calculated values of the specific surface area and the active aluminum content obtained by the established mathematical model were in good agreement with the measured values. The thermal oxidation process of the sample was divided into three stages. When the temperature rose to 1100 °C, the thermal oxidation efficiency of the sample reached 98.55%. With the increase in treatment temperature, dramatic crystalline changes occurred on the surface of the sample: amorphous alumina—γ-Al₂O₃, α-Al₂O₃, and the oxide layer thickness increased from 3.96 to 5.72 nm and 31.56 nm up to 320.15 nm. When the temperature reached 700 °C, the outer surface of the oxide layer contained a small amount of α-Al₂O₃, while the interior consisted of a large amount of γ-Al₂O₃, indicating that the conversion of γ-Al₂O₃ to α-Al₂O₃ occurred from the inside out.     

Study of CuCl2 Supported on SiO2 and Al2O3

The nature and stability of surface species of CuCl₂ supported on α-Al₂O₃, γ-Al₂O₃, and SiO₂ were investigated by using X-ray diffraction techniques and reflectance spectroscopy. No specific chemical interaction of CuCl₂ is observed on an inert α-Al₂O₃ support, as opposed to hydrated carriers as SiO₂ and γ-Al₂O₃. On these supports the coordination sphere of Cu²⁺ consists of surface groups (OH^? or O^? at drying and activation, resp.), H₂O and Cl^?, with the H₂O ligands decreasing in concentration in the process of impregnation, drying and calcination. γ-Al₂O₃ samples, calcined at 400°C, show γ-Cu₂(OH)₃Cl as opposed to CuAl₂O₄ at higher temperatures. The absence of Cu₂(OH)₃Cl on SiO₂-supported samples is related to the acid-base characteristics of the carriers. The various supports can be arranged in the following order of stability of the complexes formed: γ-Al₂O₃ > SiO₂ ? -Al₂O₃.     

Role of metal Cu species on methyl laurate catalytic hydrogenation to oxygen-containing compounds

The Cu/γ-Al₂O₃ catalysts with different Cu loadings were prepared by impregnation method. The physicochemical properties of these Cu/γ-Al₂O₃ catalysts were characterized by H₂-TPR, XRD, and in-situ XPS. The catalytic hydrogenation performances of methyl laurate over Cu/γ-Al₂O₃ catalysts were studied. The results show that the hydrogenation performances of methyl laurate on Cu/γ-Al₂O₃ catalyst are related to the dispersion, crystallite size, and content of the active component Cu⁰. The 10CA catalyst has the best hydrogenation performances for methyl laurate to produce C₁₂ alcohol. At 300 °C, the conversion of methyl laurate and the selectivity of C₁₂ alcohol are 55.6% and 30.4%, respectively.     

Phase transitions and surface stability of the WO3γ-Al2O3 system

The solid state transitions of the WO₃γ-Al₂O₃ system have been investigated in the temperature range 873–1323 K. The formation of α-Al₂O₃ and Al₂(WO₄)₃ phases and the thermal desorption of W(VI) attached to the γ-Al₂O₃ surface have been studied as function of the treatment time. The inhibition of the phase transition to α-Al₂O₃ and therefore the stabilization of the surface has been observed at 1323 K for samples with 7% WO₃ content. This stabilization is critically affected by the tungsten content. An explanation for the stabilization of the alumina surface is proposed.     

Synthesis and characterization of α-, β-, and γ-Ga2o3 prepared from aqueous solutions by controlled precipitation

α, β and γ-Ga₂O₃ have been successfully obtained in an easily scalable synthesis using aqueous solution of gallium nitrate and sodium carbonate as starting materials without any surfactant and additive. α and β-Ga₂O₃ were obtained by calcination at 350 and 700 °С, respectively, of α-GaOOH, prepared by controlled precipitation at constant pH 6 and T = 55 °С, with 24 h of aging. Aging was necessary to fully convert the initially preciptated gel into a well-crystalline and phase-pure material. γ-Ga₂O₃ was obtained after calcination at 500 °С of gallia gel, synthesized at constant pH 4 and T = 25 °С, without aging. These three polymorphs have a for gallia relatively high surface area: 55 m²/g (α-Ga₂O₃), 23 m²/g (β-Ga₂O₃) and 116 m²/g (γ-Ga₂O₃). The combination of X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), nitrogen physisorption and thermogravimetry (TG) was employed to characterize the samples and their formation.     

Influence of titanium oxide on the surface interactions of MO (M=Cu and Ni)/γ-Al2O3 catalysts

The influence of titanium oxide on the surface interactions of MO (M=Cu and Ni)/γ-Al₂O₃ catalysts has been studied by using XRD, LRS and XPS. For the catalysts with titania loadings lower than 0.56 mmol Ti⁴⁺/100 m² Al₂O₃ (i.e., the dispersion capacity), the dispersion of MO oxides on the surface of γ-Al₂O₃ support is significantly suppressed by the dispersed Ti⁴⁺ ions. The inhibiting effect is dependent on the properties of MO oxides. When titania loadings are considerably higher than the dispersion capacity, MO oxides exhibit a rather stronger interaction with the formed TiO₂ particles than the γ-Al₂O₃ support, and some of the dispersed M²⁺ ions might be accommodated by the vacant sites on TiO₂. Therefore, the catalysts can be considered as the compositions of MO/TiO₂ and MO/TiO₂/γ-Al₂O₃ (dispersed titania). TPR results show that either dispersed titania or formed TiO₂ particles can promote the reduction of copper oxide species, but the latter to a greater extent. Based on the consideration of the incorporation model, it is proposed that the surface structure of the support plays an important role in surface interactions.     

Chemical vapor infiltration method for deposition of gold nanoparticles on porous alumina supports

Knudsen’s effusion method with mass spectral analysis of the composition of the gas phase was used to measure the temperature dependence of the saturated vapor of several (CH₃)₂AuL chelate complexes and to determine the thermodynamic parameters of their sublimation. Based on the results of this study, conditions for chemical vapor deposition of gold using dimethylgold(III) chelates were chosen. Gold nanoparticles were synthesized by chemical vapor deposition (infiltration) of (CH₃)₂Au(acac) on porous granules of γ-Al₂O₃ with subsequent calcination in air at 325°C. Particle size and the chemical state of gold in Au/γ-Al₂O₃ systems were evaluated by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). A vapor infiltration procedure is suggested to prepare metallic gold particles ≤5 nm in diameter from Au/γ-Al₂O₃. It is shown that Au/γ-Al₂O₃ systems obtained by chemical vapor infiltration and containing small gold crystallites possess high catalytic activity in CO oxidation reactions at 40°C.     

Formation of Pd–Ag nanoparticles in supported catalysts based on the heterobimetallic complex PdAg<Subscript>2</Subscript>(OAc)<Subscript>4</Subscript>(HOAc)<Subscript>4</Subscript>

The formation of Pd–Ag nanoparticles deposited from the heterobimetallic acetate complex PdAg₂(OAc)₄(HOAc)₄ on α-Al₂O₃, γ-Al₂O₃, and MgAl₂O₄ has been investigated by high-resolution trans-mission electron microscopy, temperature-programmed reduction, and IR spectroscopy of adsorbed CO. The reduction of PdAg₂(OAc)₄(HOAc)₄ supported on γ-Al₂O₃ and MgAl₂O₄ takes place in two steps (at 15–245 and 290–550°C) and yields Pd–Ag particles whose average size is 6–7 nm. The reduction of the Pd–Ag catalyst supported on α-Al₂O₃ occurs in a much narrower temperature range (15–200°C) and yields larger nanoparticles (~10–20 nm). The formation of Pd–Ag alloy nanoparticles in all of the samples is demonstrated by IR spectroscopy of adsorbed CO, which indicates a marked weakening of the absorption band of the bridged form of adsorbed carbon monoxide and a >30-cm^–1 bathochromic shift of the linear adsorbed CO band. IR spectroscopic data for PdAg₂/α-Al₂O₃ suggest that Pd in this sample occurs as isolated atoms on the surface of bimetallic nanoparticles, as is indicated by the almost complete absence of bridged adsorbed CO bands and by a significant weakening of the Pd–CO bond relative to the same bond in the bimetallic samples based on γ-Al₂O₃ and MgAl₂O₄ and in the monometallic reference sample Pd/γ-Al₂O₃.     

Convenient esterification of poly(γ-glutamic acid) produced by microorganism with alkyl halides and their thermal properties

The esterification of poly(γ-glutamic acid) (γ-PGA) produced by Bacillus subtilis F2-01 with alkyl halides was carried out at 60°C in N-methyl-2-pyrrolidinone (NMP) in the presence of sodium bicarbonate to obtain the corresponding esterified γ-PGA. The thermal properties of these γ-PGA esters were examined by differential scanning calorimetry and thermogravimetry. γ-PGA esters were more stable than free acid type γ-PGA, which decomposed at 210°C. Melting temperature (T_m) of γ-PGA esters could be observed at 230-250°C. T_m of γ-PGA n-alkyl esters reached a maximum at an alkyl chain length of n = 3. © 1995 John Wiley & Sons, Inc.     

Adsorption and catalytic properties of sulfated aluminum oxide modified with cobalt ions

The adsorption properties of sulfated aluminum oxide (9% SO ₄ ^2- /γ-Al₂O₃) and a cobalt-containing composite (0.5%Сo/SO ₄ ^2- /γ-Al₂O₃) based on it are studied via dynamic sorption. The adsorption isotherms of such test adsorbates as n-hydrocarbons (C₆–C₈), benzene, ethylbenzene, chloroform, and diethyl ether are measured, and their isosteric heats of adsorption are calculated. It is shown that the surface sulfation of aluminum oxide substantially improves its electron-accepting properties, and so the catalytic activity of SO ₄ ^2- /γ-Al₂O₃ in the liquid-phase alkylation of benzene with octene-1 at temperatures of 25–120°C is one order of magnitude higher than for the initial aluminum oxide. It is established that additional modification of sulfated aluminum oxide with cobalt ions increases the activity of this catalyst by 2–4 times. It is shown that adsorption sites capable of strong specific adsorption with both donating (aromatics, diethyl ether chemosorption) and accepting molecules (chloroform) form on the surface of sulfated γ-Al₂O₃ promoted by cobalt salt.