Dy2O3 as a catalyst for a Meerwein-Ponndorf-Verley reaction

Dy₂O₃ activated at high temperature is reported as a catalyst for the liquid phase reduction of cyclohexanone. The catalytic activity of Dy₂O₃ activated at 300, 500 and 800°C and its mixed oxides with alumina for the reduction of cyclohexanone with 2-propanol has been reported. The data have been correlated with the electron donating properties of the catalysts which were reported from the adsorption of electron acceptors [EA] of various electron affinity on the surface of these oxides.     

Characterization of the active phase of NiMo/Al2O3 hydrodesulfurization catalysts

The active phase of the NiMo/Al₂O₃ catalyst for hydrodesulfurization reactions has been investigated in this work. Special attention has been focused on the effect of the order of metal impregnation on the formation of the active phase in the reaction. The Mo and Ni oxides and their sulfides on the alumina were investigated by XPS and DRS analyses. The Ni-Mo oxides or precursor of the active phase which are chemically bonded between Mo and Ni were also confirmed from the binding energy shifts of the XPS peaks. The amount of Ni-Mo oxides was determined after the formation of metal oxides during calcination. The Ni-Mo sulfide (active phase) was then induced through sulfidation. It was important that Mo should be located at the tetrahedral sites on the alumina with a high Mo dispersion. These results indicated that there are two important factors in preparing highly efficient Ni-Mo catalysts; one is that Mo should be located at the tetrahedral coordination on Al₂O₃ in high dispersion (Mo/Al₂O₃) and the other is that the Ni species should be supported on MoAl₂O₄ to form Ni-Mo oxides which change into the Ni-Mo sulfide active sites by sulfidation.     

Effects of alumina phases on CO2 sorption and regeneration properties of potassium-based alumina sorbents

A range of potassium-based alumina sorbents were fabricated by impregnation of alumina with K₂CO₃ to examine the effects of the structural and textural properties of alumina on the CO₂ sorption and regeneration properties. Alumina materials, which were used as supports, were prepared by calcining alumina at various temperatures (300, 600, 950, and 1,200 °C). The CO₂ sorption and regeneration properties of these sorbents were examined during multiple tests in a fixed-bed reactor in the presence of 1 vol% CO₂ and 9 vol% H₂O. The regeneration capacities of the potassium-based alumina sorbents increased with increasing calcination temperature of alumina. The formation of KHCO₃ increased with increasing calcination temperature during CO₂ sorption, whereas the formation of KAl(CO₃)(OH)₂, which is an inactive material, decreased. These results is due to the fact that the structure of alumina by the calcination temperature is related directly to the formation of the by-product [KAl(CO₃)(OH)₂]. The structure of alumina plays an important role in enhancing the regeneration capacity of the potassium-based alumina sorbent. Based on these results, a new potassium-based sorbent using δ-Al₂O₃ as a support was developed for post-combustion CO₂ capture. This sorbent maintained a high CO₂ capture capacity of 88 mg CO₂/g sorbent after two cycles. In particular, it showed a faster sorption rate than the other potassium-based alumina sorbents examined.     

用于CH4/CO2重整反应Ni/ZrO2-Al2O3催化剂的结构和抗积炭性能

在表面活性剂P123作用下,通过无机盐的双水解反应制备了介孔ZrO2-Al2O3复合氧化物.研究发现,所得样品具有较大的比表面积和可调变的孔结构.ZrO2可嵌入到Al2O3骨架中形成固溶体,因而热稳定性增加;与Al2O3相比,适量ZrO2加入使ZrO2-Al2O3的酸密度和酸强度增加.在CH4/CO2干气重整反应中,N...     

Synthesis of vanadium oxides nanosheets as anode material for asymmetric supercapacitor

Vanadium oxides (V₂O₅) have been intensely investigated for advanced supercapacitors due to its extensive multifunctional properties of typical layered structure and multiple stable oxide states of vanadium in its oxides. In this study, V₂O₅ nanosheets are synthesized via V₂O₅ xerogel solvothermal reaction in ethanol solvent at 200 °C for 12 h. The V₂O₅ nanosheets facilitate the easy accessibility of ions and can provide more area available for electrochemical reactions. We have achieved the highest specific capacitance of 298 F/g and good rate discharge for V₂O₅ electrodes. Notably, the capacitance still retains a high retention rate of 85% after 10,000 cycles at 200 mV/s. Furthermore, asymmetric supercapacitors is assembled based on V₂O₅ nanosheets and active carbon electrode, and a specific capacitance of 13.2 F/g is obtained at 1 A/g, with a energy density of 4.7 Wh/kg at a power density of 0.798 kW/kg and remains 2.28 Wh/kg at 7.992 kW/kg. Based on these results, the asymmetric supercapacitor exhibits a good cycle life with 77.3% capacitance retention after 3000 cycles. It suggests that the V₂O₅ nanosheets are promising electrode material for electrochemical supercapacitors.     

Surface Properties of Impregnated Mixed Oxide Catalysts

The results of a comparative study of nickel oxide-alumina and nickel oxide-silica alumina catalysts in the light of the characteristics of the support systems alumina and silica-alumina are presented. The impregnation of NiO does not produce any significant change in the textural characteristics like surface area and pore volume of the support oxides. However the deposited nickel oxide leads to the modification of the surface acidity determined by Hammett indicators. In the case of parent oxides the ammonia adsorption is strong (from heat of adsorption measurement) for alumina and silica-alumina, though for the former it is slightly stronger at comparable surface coverages. But the adsorption of ammonia on NiO? Al₂O₃ is weak while it is strong on NiO/SiO₂? Al₂O₃ at the same comparable surface coverages. The reduction in acidity is reflected in the poor dehydration and absence of skeletal isomerisation on NiO impregnated catalysts.     

Electron donating properties and catalytic activity of samarium oxide and its mixed oxides with alumina

The catalytic activity of Sm₂O₃ and its mixed oxides with alumina in the Oppenauer oxidation of a secondary alcohol and Meerwein-Ponndorf-Verley reduction of ketones is reported. The data were correlated with their surface electron donor properties. The electron donating properties of the oxides have been determined from the adsorption of electron acceptors of various electron affinity on the surface of these oxides.     

Template synthesis of ε-Fe2O3 nanoparticles in opal-like matrices

Nanoparticles of ε-Fe₂O₃ were obtained by template synthesis in the pores of opal-like matrices. The maximum content of ε-Fe₂O₃ is achieved upon calcination at 1000 °C for 2–4 h. The content of ε-Fe₂O₃ in a mixture of modifications of iron oxides reaches 80–90%, which is confirmed by the data of X-ray diffraction analysis, Mössbauer spectroscopy and magnetometry experiments.     

Characterization of new catalysts based on uranium oxides

Catalysts based on uranium oxides were systematically studied for the first time. Catalysts containing various amounts of uranium oxides (5 and 15%) supported on alumina and mixed Ni-U/Al₂O₃ catalysts were synthesized. The uranium oxide catalysts were characterized using the thermal desorption of argon, the low-temperature adsorption of nitrogen, X-ray diffraction analysis, and temperature-programmed reduction with hydrogen and CO. The effects of composition, preparation conditions, and thermal treatment on physicochemical properties and catalytic activity in the reactions of methane and butane oxidation, the steam and carbon dioxide reforming of methane, and the partial oxidation of methane were studied. It was found that a catalyst containing 5% U on alumina calcined at 1000°C was most active in the reaction of high-temperature methane oxidation. For the Ni-U/Al₂O₃ catalysts containing various uranium amounts (from 0 to 30%), the introduction of uranium as a catalyst constituent considerably increased the catalytic activity in methane steam reforming and partial oxidation.     

Gas chromatographic separation of hydrogen isotopes on columns packed with alumina,modified alumina and sol–gel alumina

The stationary phase of alumina adsorbents, prepared by different chemical processes, was used to study the separation behaviour of hydrogen isotopes. Three types of alumina, obtained by conventional hydroxide route alumina coated with silicon oxide and alumina prepared by internal gelation process (IGP), were used as packing material to study the separation of HT and T₂ in a mixture at various temperatures. The conventional alumina and silicon oxide coated alumina resolved HT and T₂ at 77 K temperature with different retention times. The retention times on SiO₂ coated columns were found to be higher than those of other adsorbents. However, the column filled with IGP alumina was found to be ideal for the separation of HT and T₂ at 240 K. The peaks were well resolved in less than 5 min on this column.     

Synthesis of ferrocene-based phosphine ligands via Cu-catalyzed reductive coupling of ferrocenyl ketone-derived tosylhydrazones and H-phosphorus oxides

Ferrocene-based phosphine oxides with various substituents at phosphorous atoms were synthesized by Cu-catalyzed reductive coupling of ferrocenyl ketone-derived tosylhydrazones and H-phosphorus oxides. Followed by the reduction of ferrocene-based phosphine oxides, 1-substituted ferrocene-based phosphine ligand 7 and 1,1′-disubstituted ferrocene-based phosphine ligand 9 were obtained. Josiphos type ligand 8 were produced after ortho-lithiation of 7 and trapping with chlorodiphenyl phosphine or chlorodicyclohexylphosphine.     

Oxidation States of Iron in Doped TiO2-SiO2 Sol-Gel Powders: A 57Fe Mössbauer Study

Ceramic coatings obtained by sol-gel routes are more and more attractive for protective purposes. Improved resistance against wet corrosion of steels can be obtained by doping the covering layer with elements like for instance transition ones. It is of major importance to have a clear-cut knowledge of the oxidation state of the doping element, especially after different heat treatments which usually follow the deposition process. Here we report about the oxidation states of 5 wt.% iron doped TiO₂, SiO₂ and mixed sol powders obtained by the sol-gel method with alkoxide precursors added with FeSO₄, 7 H₂O in organic medium. The evolution of the Fe oxidation state versus various heat treatments is followed by ⁵⁷Fe Mössbauer spectrometry supplemented by XRD data. As-dried samples are amorphous and contain ferric Fe cations, with a local distorted oxygen environment. After heating at 500°C during 3 min, ferrous and ferric oxides are evidenced together solely for silica and mixed silica-titania powders, in marked contrast with titania powders where only ferric species exist. The complete ferric state is restored for all samples after annealing at 900°C for one hour.     

Synthesis of mesoporous alumina through photo cross-linked poly(dimethylacrylamide) hydrogels

Catalysis plays a central role in many fields of life, e.g., in biochemical processes, to reduce energy costs and resources in chemical industry and to decrease or even avoid environmental pollution and in energy management. Porous alumina (Al₂O₃) is an essential material in various applications, especially as a support material for catalysts. It is often prepared by nanocasting using porous carbon materials that serve as rigid structure matrices. In this work, an alternative way to synthesize mesoporous Al₂O₃ by using hydrogels as porogenic material is presented. Hydrogels can easily be patterned by light and used to imprint their structure onto alumina opening a new approach to fabricate patterned Al₂O₃. The hydrogels used in this work are based on poly(dimethylacrylamide) and were photo-chemically cross-linked. Followed by a nanocasting process, mesoporous alumina samples were synthesized and characterized by N₂ physisorption and X-ray diffraction. The cross-linker amount in the polymer network was varied and the influence on the properties of the Al₂O₃ is analyzed.     

Determination of Polycyclic Aromatic Hydrocarbons in Vegetables by Headspace SPME-GC

Inverse gas chromatography (IGC) at infinite dilution is a powerful technique to characterize the superficial and interfacial properties of solid substrates as oxides, polymers or polymers adsorbed on oxides. It can also be used to determine the physicochemical properties and the transition phenomena of polymers. In this paper, IGC was used to determine the changes, as a function of temperature, of the specific free enthalpy ??G _a ^SP and deduce the specific entropy ??S _a ^SP of poly (methyl methacrylate) (PMMA) adsorbed on alumina or on silica for different tacticities of PMMA. The study of the surface properties of PMMA/SiO₂ and PMMA/Al₂O₃, revealed an important difference in the physicochemical behaviour of oxides covered by various concentrations of PMMA. This study also highlighted an important effect of the tacticity of the polymer on the specific entropy of PMMA adsorbed on oxides.     

Synthesis of mixed metal oxide nanoparticles of SnO<Subscript>2</Subscript> with SrO via sol–gel technology: their structural,optical, and electrical properties

Mixed metal oxides of tin with strontium (xSnO₂.SrO) in different molar ratio {where x?=?1 (1), 2 (2), 4(3); SnO₂ doped with Sr⁺²(4), SnO₂ doped with Sr⁺² and co-doped with F^?(5)} have been prepared by sol–gel technology in basic medium using SnCl₂.2H₂O as precursor in isopropanol as solvent. Structural analysis by XRD patterns have shown formation of particles at nanoscale and phase separation of SnO₂ in tetragonal rutile framework in these mixed metal oxides. This fact was further supported by TEM. SEM images of all these samples have shown formation of various geometrical patterns ranging from spherical particles to nanorods. In the IR spectra of all these oxides, Sr–O absorption bands were present only in sample (1). UV–Vis spectroscopy has shown reduction in optical band gap in mixed metal oxides and the lowest value of band gap was observed for sample (3). Photoluminescence spectra of all these derivatives are found to be almost similar again indicated retention of tetragonal rutile SnO₂ framework. I–V curves of all these oxides are non-linear and lowest resistance was observed for sample (3). This fact was further supported by impedance measurements.

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Microporous Crystalline γ‐Al2O3 Replicated from Microporous Covalent Triazine Framework and Its Application as Support for Catalytic Hydrolysis of Ammonia Borane

Significant progress has been made on the synthesis and application of mesoporous γ‐alumina. To date, little attention has been paid to the synthesis of microporous crystalline alumina. Here, fabrication of microporous crystalline γ‐alumina using a microporous covalent triazine framework (CTF‐1) as a template is described. Microporous crystalline γ‐alumina with a micro‐meso binary pore system was replicated by infiltration of aluminum nitrate into the micropores of the CTF‐1 template through a NH₃/water‐vapor‐induced internal hydrolysis method, followed by thermal treatment, and subsequent removal of the CTF‐1 template with a 30 % H₂O₂ aqueous solution. The obtained crystalline γ‐alumina material exhibits a large surface area (349 m² g⁻¹) with micropore distribution centered at about 1.27 nm. Ru supported on microporous γ‐Al₂O₃ can be employed as catalyst for hydrolytic dehydrogenation of ammonia borane, and it exhibits high catalytic activity and good durability. This finding provides a new benchmark for preparing well‐defined crystalline microporous alumina materials by a template method, which can be applied in a wide range of fields.     

Characterization of Silica-Containing Aluminum Hydroxide and Oxide Aerogels

Pure and silica-containing Al hydroxide aerogels were prepared by the supercritical drying method. The samples were later calcined, giving rise to alumina and Si–Al mixed oxides. The materials were characterized from the points of view of their bulk and surface structures. The Si-free material before calcination is well-crystallized boehmite that converts to γ-alumina by calcination. The silica-containing hydroxides are composed of boehmite layers with silicates in the interlayer region. The resulting mixed oxides present silica essentially in the bulk. The surface structure of alumina seems poorly sensitive to silica addition. Surface silanol groups appear only for SiO₂more than 4%. No Brønsted acidity appears. Silica addition allows mixed oxides with higher surface areas to be obtained.     

Mehrfachbindungen zwischen Hauptgruppenelementen und Übergangsmetallen: LXX. Erste Arylrheniumoxide (σ-Aryl)ReO3

The first examples of arylmetal oxides of general formula (σ-aryl)MO_x have been synthesized, for M = Re. The compounds (σ-aryl)ReO₃ (3) are obtained in a simple, ostensibly general route by treatment of dirhenium heptoxide with the corresponding arylzinc compound Zn(σ-aryl)₂. As side product, the zinc perrhenate Zn(thf)₂(ReO₄)₂ formed and precipitated as insoluble material from the solution. (Mesityltrioxo)rhenium(VII) was characterized by an X-ray diffraction study (pyramidal geometry).     

P-chirogenic phosphines. MOP/diPAMP hybrids, their oxide crystal structures, reduction studies and alternative syntheses

The novel P-chirogenic anisylphenylMOP derivatives (R,R) and (R,S)-2-(anisylphenylphosphino)-2′-methoxy-1,1′-binaphthyl (10a and b) have been synthesized and their corresponding oxides characterised by X-ray crystallography. The results of a parallel screening regimen with various reducing agents highlight the sensitivity of the tertiary phosphine oxides to epimerisation and, interestingly, reveal that the PO, O-CH₃ and P-C₆H₅ bonds can all be cleaved selectively depending on the reducing agents employed. An alternative synthesis was provided by direct coupling of the secondary phosphine with (R)-methoxytriflate 4, which led to the isolation of the optically pure P-chirogenic phosphines via their borane adducts. A brief study of the coordination chemistry of 10a with different rhodium precursors, relevant to the catalytic asymmetric addition of boronic acids to aldehydes is also reported.     

Surface structure and redox chemistry of ceria-containing automotive catalytic systems

A summary is given of recent work done at the authors' laboratory, using several spectroscopies, molecular modeling and catalytic activity tests, to study the surface reactivity of ceriacontaining high surface area solids useful for automotive exhaust depollution catalysis. Issues addressed include the influence of the basicity of the cerium ion ligand environment on its ability for activation of O₂ at the material surface, and its modification by supporting on alumina or doping with Cl⁻ or other anions; the tendency to grouping of oxygen vacancies at the CeO₂ (111) surface; the higher ease for formation of surface reduced centers in mixed (Zr,Ce) oxides; and the effect of electronic transfer and other chemical interactions induced by ceria on the redox reactivity of transition metalcontaining catalysts.