Dehydrogenation of Isobutane Over V2O5/γ-Al2O3 Catalyst

The effect of the type of the support and the amount of V₂O₅ loading on the activity of V₂O₅/γ-Al₂O₃ catalyst for the dehydrogenation of isobutane have been investigated. Based on the experimental results of TPR, XRD and ESR spectroscopy, it is suggested that there are strong interactions between vanadia and carrier and that the V⁴⁺ species on the surface is the active site of V₂O₅/γ-Al₂O₃ for this reaction. This revised version was published online in June 2006 with corrections to the Cover Date.     

Structural and spectroscopic characterization of Al2−x Cr x O3 powders obtained by polymeric precursor method

Al₂O₃ and Al_2−x Cr _x O₃ (x = 0.01, 0.02 and 0.04) powders have been synthesized by the polymeric precursors method. A study of the structural evolution of crystalline phases corresponding to the obtained powders was accomplished through X-Ray Diffraction and UV-vis spectroscopy (reflectance spectra and CIEL^*a^*b^* color data). The obtained results allow to identify the γ-Al₂O₃ to α-Al₂O₃ phase transition. The single-phase α-Al₂O₃ powder was obtained after heat treatment at 1050 °C for 2 h. The results show that the green to red color transition and ruby luminescence lines observed for the powders of Al_2−x Cr _x O₃ are related to the γ to α-Al₂O₃ phase transition and the temperature and time range for such transition depends on the chromium content.     

Calorimetric Characterization of Surface Reactivity of Supported Ga2O3 Catalysts

The surface properties of supported gallium oxide catalysts prepared by impregnation of various supports (γ-Al₂O₃, SiO₂, TiO₂, ZrO₂) were investigated by adsorption microcalorimetry, using ammonia and water as probe molecules. In the case of acidic supports (γ-Al₂O₃, ZrO₂, TiO₂), the acidic character of supported gallium catalysts always decreased in comparison with gallium-free supports; on very weakly acidic SiO₂, new acidic centers were created when depositing Ga₂O₃. The addition of gallium oxide decreased the hydrophilic properties of alumina, titania and zirconia, but increased the amount of water adsorbed on silica. The catalytic performances in the selective catalytic reduction of NO by C₂H₄ in excess oxygenwere in the order Ga/Al₂O₃>Ga/TiO₂>Ga/ZrO₂>>Ga/SiO₂. This order is more related to the quality of the dispersion of Ga₂O₃ on the support than to the global acidity of the solids. This revised version was published online in July 2006 with corrections to the Cover Date.     

Catalytic properties of Pt/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts in the aqueous-phase reforming of ethylene glycol: Effect of the alumina support

The influence of the alumina support on the catalytic activity of Pt/Al₂O₃ catalysts in aqueous phase reforming of ethylene glycol to hydrogen was studied. The catalysts were prepared by impregnation of γ-, δ-, and α-alumina with H₂PtCl₆. The highest rate of hydrogen production (452 μmol min⁻¹ g⁻¹) obtained with the Pt/α-Al₂O₃ catalyst can be related to the highest extent of dispersion of Pt on α-Al₂O₃. XPS, TEM-EDX and TPR-H₂ measurements showed the absence of chloride-containing surface complexes in the Pt/α-Al₂O₃ catalyst. However, chloride-containing entities were found on the surface of Pt/γ-Al₂O₃ and Pr/δ-Al₂O₃ catalysts. When chloride ions are removed chlorinated Pt species facilitate the sintering of Pt crystallites and in this way affect the extent of Pt dispersion. Moreover, depending upon the particular crystalline form, alumina atoms have different coordination and alumina surfaces contain varying amounts of OH groups of different nature which affect the interaction between Pt and the support.     

Sol–gel synthesis,characterization and photocatalytic activity of mesoporous TiO<Subscript>2</Subscript>/γ-Al<Subscript>2</Subscript>O<Subscript>3 </Subscript>granules

Mesoporous TiO₂/γ-Al₂O₃ composite granules were prepared by combining sol–gel/oil-drop method, using various titania solution. The product granules can be used as a photocatalyst or adsorbent in moving, fluidized bed reactors. The phase composition and pore structure of the granules can be controlled by calcination temperature and using different titania solution. In the photocatalysis of NH₃ decomposition, TiO₂/γ-Al₂O₃ granules using Degussa P25 powder treated thermally at 450 °C showed the highest catalytic ability. However, TiO₂/γ-Al₂O₃ granules using titania made by hydrothermal method had comparable performance in NH₃ decomposition.     

Voltammetric determination of the trace amounts of bromate in drinking water after pre-concentration on hydrous γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

A differential pulse voltammetric (DPV) method for the determination of bromate in drinking water, after pre-concentration on γ-Al₂O₃, is proposed. The reduction peak of bromate has been observed at the potential E _p -−1.6 V in an ammonia buffer as a supporting electrolyte. The method has been successfully applied to determine a bromate concentration of 2.5 μg·l⁻¹ in drinking water (RSD=6.1%, n=7). A sample pre-treatment with a column filled with mixed cation-exchange resin in Ag, Ba and H forms was needed before pre-concentration of bromate on alumina.     

Preparation,characterization and thermal decomposition of phenylenediammonium sulfate salts Part. XVI

Polyaniline/α-Al₂O₃ (PANI/α-Al₂O₃) composites were synthesized by in situ polymerization through ammonium persulfate ((NH₄)₂S₂O₈, APS) oxidized aniline using HCl as dopant. XRD and FTIR were used to characterize the PANI/α-Al₂O₃ composites. The thermal stabilities and glass transition temperature (T _g) of PANI/α-Al₂O₃ composites were tested using thermogravimetric (TG) method and modulated differential scanning calorimetry (MDSC) technique. The results of TG showed that the thermal stability of PANI/α-Al₂O₃ composite increased and then decreased with the increase in α-Al₂O₃ content. The derivative thermogravimetry (DTG) curves showed one step degradation of PANI when the α-Al₂O₃ content was lower than 52.5 mass%, and exhibited two steps degradation when the α-Al₂O₃ content was higher than 63.6 mass%. The MDSC curves showed that the T _g of PANI/α-Al₂O₃ composites increased and then decreased with the augment of α-Al₂O₃ for the interaction between PANI chains and the surface of α-Al₂O₃.     

Pt LIII-edge XANES and EXAFS studies on γ-Al2O3 supported Pt catalysts

Pt L_III-edge XANES and EXAFS were employed to investigate the nature of Pt/γ-Al₂O₃, Pt−Sn/γ-Al₂O₃ and Pt−Fe/γ-Al₂O₃ catalysts. The results indicated that Pt species on these catalysts were all in the oxidized states before reduction, and in the metallic states after reduction. The dispersity of the Pt species on the catalysts was very high after reduction. The electronic properties of the highly dispersed Pt species were different from that of the bulk Pt in large crystallites. An interaction between Pt and the metal-oxide modified γ-Al₂O₃ support is proposed. The interaction improved the dispersity of the Pt species on the catalysts and is thought to be the reason for the enhanced activity and selectivity for dehydrogenation reactions over these catalysts.     

Preparation of compact Al2O3 film on metal for oxidation resistance by polyvinylpyrrolidone

Oxidation resistance of metal at high temperature can be improved by an environmentally friendly solution deposition approach. Stable precursor solution with high oxide concentration, favorable viscosity and low surface tension was prepared using aluminum sec-butoxide (ASB) and polyvinylpyrrolidone (PVP) as starting raw materials. Alumina sol-gel films were deposited onto metal by spin-coating followed by heat treatment. When PVP was added according to an amount of 50 mg/mL into a sol with an ASB/H₂O molar ratio of 1:35, the as-obtained sol exhibited favorable gelation time and viscosity. The surface tension of the alumina sol with PVP was examined to be lower by 32% than the sol (ASB:H₂O = 1:100) without PVP. TG-DTA analyses show the densification of the alumina gel film with PVP was progressed within a wide temperature range from 200 to 650 °C. Crack-free Al₂O₃ film with a thickness up to 1.5 μm was successfully produced on metallic substrate by three spin-coating cycles. SEM and XRD analyses revealed the gel film transformed into compact α-Al₂O₃ material after calcined at 1,000 °C for 0.5 h. The weight gained by the samples during firing at 1,000 °C indicated that the Al₂O₃ coating film could reduce the rate of oxidation by ∼81%. The hardness of the Al₂O₃ film coated metal was higher by 260% than the uncoated metal that was calcined at 1,000 °C for 0.5 h. It was confirmed by adhesion test that both the alumina/PVP hybrid film and the as-produced α-Al₂O₃ coating film had strong adhesion.     

Effect of Fe-modified α-Al2O3 on the properties of Pd/α-Al2O3 catalysts in selective acetylene hydrogenation

The use of nanocrystalline Fe-modified α-Al₂O₃ prepared by sol–gel and solvothermal method as supports for Pd catalysts resulted in an improved catalyst performance in selective acetylene hydrogenation. Moreover, the amount of coke deposits was reduced due to lower acidity of the Fe-modified α-Al₂O₃ supports.     

Effects of the support crystallite size and the reduction temperature on the properties of Pd/α-Al2O3 catalysts in selective acetylene hydrogenation

Pd catalysts supported on the solvothermal-derived nanocrystalline α-Al₂O₃ (45 nm) exhibited superior performances in the selective acetylene hydrogenation than those supported on micron-sized ones (44–149 μm). Reduction at 500°C led to an improvement of the ethylene yield for the Pd/nanocrystalline α-Al₂O₃, but not for the Pd/micron-sized α-Al₂O₃.     

Al NMR studies of Ce-Al mixed oxides: origin of 40 ppm peak

CeO₂-γ-Al₂O₃ mixed oxides have been prepared by using both co-precipitation and impregnation methods followed by calcination at 650°C and investigated by ²⁷Al MAS NMR, powder X-ray diffraction and temperature programmed reduction techniques to understand the nature of chemical interaction existing between CeO₂ and γ-Al₂O₃. The ²⁷Al NMR spectra of CeO₂-containing samples showed an additional peak placed at 40 ppm along with the two peaks at 68 and 6 ppm which originate from the tetrahedrally and octahedrally coordinated Al³⁺ ions present in γ-Al₂O₃. As the concentration of CeO₂ in the mixed oxide increased, the intensity of the 40 ppm peak increased and this was the prominent peak for CeO₂-rich mixed oxide samples. The origin of this 40 ppm peak is discussed and it is inferred that this peak is due to Al³⁺ ions, which are present in CeO₂ lattice, forming a solid solution.     

Highly Dispersed Ce x Zr1−x O2 Nano-Oxides Over Alumina, Silica and Titania Supports for Catalytic Applications

We have been exploring the utilization of supported ceria and ceria–zirconia nano-oxides for different catalytic applications. In this comprehensive investigation, a series of Ce _x Zr_1−x O₂/Al₂O₃, Ce _x Zr_1−x O₂/SiO₂ and Ce _x Zr_1−x O₂/TiO₂ composite oxide catalysts were synthesized and subjected to thermal treatments from 773 to 1073 K to examine the influence of support on thermal stability, textural properties and catalytic activity of the ceria–zirconia solid solutions. The physicochemical characterization studies were performed using X-ray diffraction (XRD), Raman spectroscopy (RS), X-ray photoelectron spectroscopy (XPS), and high-resolution transmission electron microscopy (HREM), thermogravimetry and BET surface area methods. To evaluate the catalytic properties, oxygen storage/release capacity (OSC) and CO oxidation activity measurements were carried out. The XRD analyses revealed the formation of Ce_0.75Zr_0.25O₂, Ce_0.6Zr_0.4O₂, Ce_0.16Zr_0.84O₂ and Ce_0.5Zr_0.5O₂ phases depending on the nature of support and calcination temperature employed. Raman spectroscopy measurements in corroboration with XRD results suggested enrichment of zirconium in the Ce _x Zr_1−x O₂ solid solutions with increasing calcination temperature thereby resulting in the formation of oxygen vacancies, lattice defects and oxygen ion displacement from the ideal cubic lattice positions. The HREM results indicated a well-dispersed cubic Ce _x Zr_1−x O₂ phase of the size around 5 nm over all supports at 773 K and there was no appreciable increase in the size after treatment at 1073 K. The XPS studies revealed the presence of cerium in both Ce⁴⁺ and Ce³⁺ oxidation states in different proportions depending on the nature of support and the treatment temperature applied. All characterization techniques indicated absence of pure ZrO₂ and crystalline inactive phases between Ce–Al, Ce–Si and Ce–Ti oxides. Among the three supports employed, silica was found to stabilize more effectively the nanosized Ce _x Zr_1−x O₂ oxides by retarding the sintering phenomenon during high temperature treatments, followed by alumina and titania. Interestingly, the alumina supported samples exhibited highest OSC and CO oxidation activity followed by titania and silica. Details of these findings are consolidated in this review.     

Isolation of lappaconitine from Aconitum septentrionale roots by adsorption

Extracts of Aconitum septentrionale Koelle roots obtained using chloroform, isopropanol, and ethanol were purified using chloroform and basic γ-Al₂O₃. Ballast materials were selectively adsorbed by γ-Al₂O₃, increasing the mass fraction of lappaconitine in the extract. The ethanol extract was purified most. The degree of lappaconitine extraction by chloroform was unaffected by the presence of γ-Al₂O₃. However, the mass fraction in the extract and lappaconitine extraction from Aconitum septentrionale were increased more than twice. __________ Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 274–276, May–June, 2006.     

Hydrogenation of 2-ethylanthraquinone over Pd/Zro2-γ-Al2O3 catalyst

A ZrO₂-γ-Al₂O₃ supported Pd catalyst was prepared and characterized by XRD, XPS, H₂-TPR and TEM techniques. The catalytic activity was evaluated in the liquid-phase hydrogenation of 2-ethylanthraquinone. Comparing with Pd/γ-Al₂O₃, it showed high catalytic activity.     

Catalytic Combustion of Methane over CeO2-MOx (M=La, Ca) Solid Solution Promoted Pd/γ-Al2O3 Catalysts

Solid solution CeO₂-MO_x (M=La³⁺, Ca²⁺) promoted Pd/γ-Al₂O₃ catalysts were prepared by a deposition-precipitation method. The structural properties were investigated by X-ray diffraction, X-ray photoelectron spectroscopy, and Raman spectroscopy. The results showed that Mⁿ⁺ ions incorporated into CeO₂ lattice and solid solutions formed in Pd/γ-Al₂O₃-CeO₂-MO_x catalysts. The formation of solid solution was confirmed by the change in lattice parameters of CeO₂ and the shift of 2θ angles as compared with pure CeO₂. A strain formed in the O²⁻ sub-lattice of CeO₂ was revealed by Raman analyses, which decreased the intensity of the Raman-active band at around 463 cm⁻¹ owing to the F_2g symmetric stretching of Ce−O bond. The appearance of a new band at 615 cm⁻¹ (in the case of Pd/γ-Al₂O₃-CeO₂-CaO) and a shoulder at 320 cm⁻¹ (in the case of Pd/γ-Al₂O₃-CeO₂-La₂O₃) was also confirmed. Ionic Pd^δ+ species were formed in the catalysts, which exhibited higher binding energies (0.5−0.6 eV higher for Pd 3d_5/2) than that of normal PdO. The catalysts showed high activity and stability for low temperature methane combustion. 10% and 100% conversions of methane could be obtained at temperatures of 254 and 340 °C, respectively, over Pd/γ-Al₂O₃-CeO₂-La₂O₃ catalyst under an hourly space velocity of 50000 h⁻¹.     

Synthesis of Eu2O3 nanowire arrays through a facile sol–gel template approach

Eu₂O₃ nanowire arrays embedded in anodic alumina membranes (AAMs) were fabricated by an improved sol–gel method. They have cubic structures with uniform diameter of about 40 nm. The emission spectra of Eu₂O₃ consist of one main line at 613 nm under 377 nm excitation, which shows the electric dipole transition ⁵D₄→⁷F₅ (at 613 nm) is the strongest.     

Thermal degradation of iron chelate complexes adsorbed on mesoporous silica and alumina

Nanometric Fe₂O₃ particles could be inserted inside the internal pore volume of SBA-15 mesoporous silica and mesoporous alumina supports, when Fe(III) chelates (EDTA, gluconate or citrate) were used as impregnating precursors. The oxidative degradation of the chelating anions was followed by combined TG-DTA. Strong chelate-SiOH interactions (case of bulky EDTA), favored by the mesopore curvature, yield sub-nanometric extremely well dispersed Fe₂O₃ particles preferentially located at the micropore mouths (confinement effect). Fe₂O₃ even more strongly interacts with alumina walls, generating either (Fe,Al)₂O₃ mixed phases or Fe-aluminate micro domains. These iron-based mesoporous alumina composites proved very active catalysts in total oxidation of phenol at ambient conditions, with extremely low iron leaching (0.2%).     

Mo_2C/γ-Al_2O_3催化剂上苯加氢反应的原位红外光谱研究

采用程序升温反应法制备了钝化态、还原钝化态和新鲜态Mo2C/γ-Al2O3催化剂,结合原位红外光谱表征技术和反应性能评价,考察、比较了三种催化剂苯加氢反应活性.原位红外光谱结果表明,新鲜态Mo2C/γ-Al2O3催化剂在室温就显示了较好的苯加氢反应活性,表现了类贵金属的催化活性.CO吸附在反应前后新鲜态Mo2C/γ-Al2O3催化剂上的对比结果表明,低价态的Mo位(Moδ+(0δ2))是苯加氢反应活性中心.三种催化剂的反应活性结果表明,新鲜态Mo2C/γ-Al2O3催化剂反应活性最好,催化剂寿命最长,失活之后在500°C下H2处理即可恢复原有活性.