Structural properties and magnetic interactions in Al3+ and Cr3+ co-substituted CoFe2O4 ferrite

A series of CoAl_xCr_xFe_2−2xO₄ systems (x = 0.1 to 0.5 in steps of x = 0.1) spinel ferrites have been synthesized successfully using wet chemical co-precipitation technique. The samples were characterized by X-ray diffraction (XRD), infrared spectroscopy (IR) and magnetization measurements. The powder XRD patterns confirm the single phase spinel structure for the materials synthesized. X -ray diffraction measurements were performed to yield the lattice constant as function of the amount x corresponding to Al-Cr substitution. Lattice parameters, X-ray density, bulk density and particle size decrease whereas porosity increases with the increase in Al-Cr content, ‘x’. Infrared studies show two absorption bands at about 400 cm⁻¹ and 600 cm⁻¹ for octahedral and tetrahedral sites, respectively. Saturation magnetization decreases with the increase in Al-Cr content x. AC magnetic susceptibility measurements were carried out as a function of temperature to measure the Curie temperature, which was found to decrease with Al-Cr content x. The decrease of Curie temperature has been explained by A-B interaction.      

Formation of aromatic carbonium ions on V2O5/Al2O3

A comparison of IR spectra of individual toluene, mesitylene, hexamethylbenzene, triene and their carbonium ions with IR spectra of the same molecules adsorbed on V₂O₅/Al₂O₃ has indicated the formation of carbonium ions on catalyst surface.

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- , , , , - , V₂O₅/Al₂O₃ Al₂O₃, t, V₂O₅/Al₂O₃ .

     

有序介孔Al2O3∶RE3+的制备及Gd3+对Eu3+的能量传递

以P123为表面活性剂,异丙醇铝为铝源,用简易溶胶-凝胶法,获得了单掺和双掺Gd3+,Eu3+的介孔氧化铝组装体。用广角X-射线衍射仪(WAXD)进行了物相分析;小角X-射线衍射仪(SAXD)、比表面仪进行了孔结构分析和形貌表征;研究了组装体的发光性能并发现Gd3+对Eu3+有能量传递作用,并分析了能量传递过程。     

Hydration of the ions Al3+ and Cu2+. An ab initio SCF study

Ab initio calculations are reported for the systems Al(H₂O)_n³⁺ and Cu(H₂O)_n²⁺ with n up to 7. The calculated binding energies increase monotically up to n = 6, with equal binding energies for n = 6 and 7 for the Al³⁺ cation. An estimate of the enthalpy of hydration of Al³⁺ is given, based on model calculations with one or two water molecules from the second solvation shell. An SN1 (dissociative) mechanism for the exchange of the water molecules from the first hydration shell of Al³⁺ appears energetically favorable if the leaving molecule remains in the second hydration shell.     

TPR studies on steam reforming of 2-propanol on Rh/Al2O3, Ru/Al2O3 and Pd/Al2O3

Reaction pathways for steam reforming of 2-propanol (isopropyl alcohol, IPA) on Rh/Al₂O₃, Ru/Al₂O₃ and Pd/Al₂O₃ have been studied by temperature-programmed reactions (TPRs) of IPA and acetone in the presence of steam. The results of TPRs suggest that that of IPA on Rh/Al₂O₃ and Ru/Al₂O₃ proceeds via acetone, while the steam reforming of IPA on Pd/Al₂O₃ takes place via propene from acetone. This revised version was published online in August 2006 with corrections to the Cover Date.     

Sulfurization of Pt/Al2O3?Cl catalysts. IV. Adsorption sites of H2S on Al2O3, Al2O3?Cl and Pt/Al2O3?Cl

Chemisorption of H₂S on Al₂O₃, Al₂O₃–Cl and Pt/Al₂O₃–Cl has been studied by gravimetry and IR spectroscopy. The influence of the amount of Cl on the H₂S adsorption equilibrium value and the nature of the adsorption sites at low and high coverages are discussed.

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H₂S Al₂O₃, Al₂O₃–Cl Pt/Al₂O₃–Cl . Cl H₂S, .

     

X-ray study of Re/Al2O3 and Re+Pt/Al2O3 catalysts using synchrotron radiation

Uning synchrotron radiation, L_III rhenium absorption spectra have been studied for Re/Al₂O₃ and Re+Pt/Al₂O₃ catalysts obtained by impregnation. For individual rhenium compounds a linear dependence between the shift of absorption edge and the state of rhenium oxidation has been found. The absorption spectra of reduced catalysts are significantly broadened as compared with those of individual compounds of the same valency. This points to the presence of rhenium compounds in different oxidation states.

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L_III- , Re/Al₂O₃ Re+Pt/Al₂O₃, . . . .

     

Sulfuration of Pt/Al2O3, Pt?Re/Al2O3 and Pt?Ir/Al2O3 catalysts

Three reforming catalysts Pt/Al₂O₃, Pt–Ir/Al₂O₃ and Pt–Re/Al₂O₃ have been sulfurated by H₂S and tested by their activities in benzene hydrogenation. By treatment at 500°C under hydrogen flow only a part of the initial activity of the non-sulfurated catalyst is retained. So only a part of the adsorbed sulfur is easily removed in these conditions. The remaining sulfur for each of the catalysts (Pt/Al₂O₃, Pt–Ir/Al₂O₃ and Pt–Re/Al₂O₃) gives the same atomic ratio of 0.5 sulfur atom per accessible metallic atom.

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Pt/Al₂O₃, Pt–Ir/Al₂O₃ Pt–Pe/Al₂O₃ . 500°C H₂ . . ., . (Pt/Al₂O₃, Pt–Ir/Al₂O₃ Pt–Pe/Al₂O₃) 0,5.

     

Cyclohexene skeletal isomerization activity of sepiolites modified with B3+ or Al3+ ions

The effect of sepiolite modification by B³⁺ and Al³⁺ ions on catalytic performance were investigated in cyclohexene skeletal isomerization (CSI) reaction. Catalytic activity to 1- and 3-methylcyclopentenes (1- and 3-MCP) fit the Bassett-Habgood kinetic model for first order processes. These ions induced strong acidity in the sepiolite and the best results (greater activity and selectivity to 1-MCP) were found when the sepiolite was exchanged with an BF₃/methanol solution which contained 3 wt.% of the B³⁺ ion.

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B³⁺ Al³⁺ . 1- 3- - . . - 1-- , BF₃/, 3 . % B³⁺.

     

Zur quantitativen Bestimmung von Zn2+, Pb2+, Al3+ und Cr3+

Ohne Zusammenfassung     

Investigation of the acidity of Ni/Al2O3 and Ni/SiO2?Al2O3 catalysts

Acidity of Ni-modified alumina and silica-alumina catalysts was determined using n-butylamine titration and pyridine adsorption methods. Strong influence of Ni²⁺ ions on the Brönsted acidity of silicaalumina was observed. Improved Brönsted acidity of such system was confirmed by the results of the test reaction.     

Partial oxidation of methane on Cr2O3/Al2O3

The oxidation of methane on supported chromia was studied at temperatures varying between 423 and 743 K and CH₄/O₂ ratios between 1 and 9 in a differential reactor. The main reaction products observed were carbon monoxide and formaldehyde. The rates of reaction obey a power law expression.

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, 423 743 CH₄/O₂ 1 9, . . .

     

ESR spectra and magnetic constants of α-Al2O3:Co2+,H+ and α-Al2O3 :Co2+,X+

New anisotropic ESR spectra of Co²⁺ doped sapphire, different from hitherto known, are reported. The new spectra which are observed, beside the well-known spectra of α-Al₂O₃:Co²⁺, are shown to form two sets, each one consisting of six spectra (1–6) and (7–12). The spectra of both sets are proven to be interrelated by B_3a symmetry. g and A tensors for each set will be given. Evidence is given that the two sets are to be assigned to the defects α-Al₂O₃:Co²⁺,H⁺ and α-Al₂O₃:Co²⁺,X⁺. The former is concluded to consists of a Co²⁺ ion at the substitutional site (c) and a proton located in a potential minimum along a straight line between O^2- ions situated in O²⁺ triangles above and below the CO²⁺ ion. The potential function for the proton has been calculated by quantum-chemical calculations to clucidate the geometrical structure of the paramagnetic center. The α-Al₂O₃:Co²⁺,X⁺ could not be fully analyzed but some evidence is presented, that X⁺ might be alkali ions.     

The hydration process of La2O3 studied by the electron spin resonance of Gd3+ and Mn2+ ions

The hydration of single-crystal La₂O₃ samples was studied following the evolution versus time of ESR spectra of Gd³⁺ and Mn²⁺ ions which enter the lattice substitutionally at lanthanum sites. Our results, which confirm those obtained previously on the macroscopic scale, permit a better understanding of the hydration process on the atomic scale.     

Surface acidity of the La2O3/Al2O3 system

Surface acidity of aluminium oxide containing 5 wt. % lanthanum oxide has been determined by IR spectroscopy. Strength of Lewis sites of the La₂O₃/Al₂O₃ system was lower than that of pure aluminium oxide. However, the presence of La₂O₃ in aluminium oxide increased the thermostability of these sites in the mixed system.     

Pyrolytic and catalytic conversion of rape oil into aromatic and aliphatic fractions in a fixed bed reactor on Al2O3 and Al2O3/B2O3 catalysts

In the, at present, unstable fuel market, much attention is devoted to alternative technologies for fuel production and development of alternative products of the petrochemical industry. One of the prospective sources of fuel and alternative petrochemical products is biomass, and the use of oil plants is one of the possibilities. This paper reports on a possible conversion of rapeseed oil produced in Poland into intermediate hydrocarbon fractions by pyrolysis combined with parallel catalytic conversion. The products were analysed by gas chromatography coupled with a mass detector. The process was performed in a fixed-bed reactor and was monitored by FTIR and ¹H NMR. Depending on the catalysts applied, the products contained: water, carbon oxides, hydrogen, aliphatic or aromatic hydrocarbons accompanied by some amount of C2-C5 hydrocarbons formed during the cracking process. Presented at the 35th International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 26–30 May 2008.     

Influence of the preparation method on the pore spectrum of Pt?Cr/Al2O3 and Pt?Sn/Al2O3 catalysts

It is shown that, in contrast to classical impregnation methods, in bimetallic catalyst production the texture of the carrier is stabilized by introducing the promoting ion on the surface of Pt/Al₂O₃ with vapors of CrO₂Cl₂ or SnCl₄. This is shown by a relatively slower decrease of the specific area and the volume of the pores upon calcination.

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, Pt/Al₂O₃- CrO₂Cl₂ SnCl₄ . .

     

钡改性对Cr_2O_3/Al_2O_3催化剂异丁烷脱氢性能的影响

采用浸渍法制备了不同BaO负载量的Cr_2O_3/Al_2O_3催化剂,利用XRD、BET、NH3-TPD和O2-TPO等表征方法对钡改性前后的催化剂进行了分析;在反应温度560℃、反应压力0.1MPa、催化剂用量10mL、GHSV=400h-1的条件下,在固定床反应器上考察了其异丁烷脱氢反应的性能。结果表明,钡的引入影响了活性组分Cr2O3的分散,导致了催化剂比表面积的降低,但影响并不显著;钡的引入降低了催化剂表面的酸性、减少了反应过程中催化剂的积炭,改善了催化剂的选择性,提高了催化剂的稳定性。当BaO负载量为3%时,催化剂的性能最佳。     

Effect of inert components (Y2O3, Al2O3, and Ga2O3) on the chemistimulating effect of the Sb2O3 activator of GaAs thermal oxidation

Chemistimilated thermal oxidation of gallium arsenide was studied using Sb₂O₃ activator oxide in compositions with Ga₂O₃, Al₂O₃, and Y₂O₃ inert components. For Sb₂O₃-Y₂O₃ compositions, the thickness of the resulting oxide layer on GaAs was found to be a linear function of composition over the enter range of the compositions. For antimony oxide compositions with Ga₂O₃ and Al₂O₃ inert components, nonadditivities were observed near the component ordinates. For the Sb₂O₃-Ga₂O₃ system, the chemistimulating efficiency noticeably weakened at low concentrations of the inert component. The linear trend observed for this system within 0–60 mol % Sb₂O₃ is additively determined by the oxide layer thickness on GaAs in the presence of Sb₂O₃ and in the absence of activator. In the presence of inert Al₂O₃, the chemistimulating effect was enhanced near the Al₂O₃ ordinate and the resulting function was nonadditive with respect to the thicknesses reached in the presence of the individual components.