X-ray diffraction studies of platinum-alumina catalysts in a high-temperature chamber

X-ray diffraction studies of platinum-alumina catalysts in a high-temperature chamber have revealed that for the catalysts obtained by the reduction of preactivated samples, no complete reduction of platinum takes place.

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, , , .

     

Studies of bulk and supported Cu?Cr catalysts in a high-temperature X-ray chamber

Bulk and -Al₂O₃-supported Cu–Cr catalysts have been studied in a high-temperature X-ray chamber in air, inert (He) and reducing (He+5% H₂) media. The different course of solid-phase reactions is due to the gas phase composition and the presence of a support.

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-Al₂O₃ , () (He+5%H₂) . , .

     

In situ X-ray diffraction studies of structural transformations in V-P-O catalysts

Structural transformations of V-P-O catalysts have been studied in situ in oxidative, inert and reducing atmosphere by the high-temperature X-ray diffraction method. Formation of vanadyl phosphates is shown to depend on the P/V ratio in the initial sample. It has been established that transformations in the phase composition of catalysts is independent of the reaction media at P/V=2. The effect of catalyst composition on catalytic properties is discussed.

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V-P-O , . , P/V . P/V=2. V-P-O .

     

129Xe nuclear magnetic resonance studies of supported platinum-alumina catalysts

¹²⁹Xe nuclear magnetic resonance spectra of xenon adsorbed on supported platinum-alumina catalysts have been examined. The state of metallic platinum particles (Pt^o) was shown to be different for Pt/Al₂O₃ and Pt/Al₂O₃(Cl) samples. Some assumptions about the mutual arrangement of supported metallic particles have been made.

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¹²⁹Xe , , Pt⁰ Pt(II). , (Pt⁰) , . Pt⁰ Pt(II).

     

Catalytic synthesis of C-alkylimidazoles over platinum-alumina catalysts

The synthesis of C-alkylimidazoles from 1,2-diamines and carboxylic acids over bifunctional platinum—alumina catalysts has been studied. It has been shown that this method is effective for the synthesis of 2-alkyl and 2,4-dialkylimidazoles including imidazoles with long-chain alkyls. The effect of the reaction temperature, space velocity of the flow of the raw materials, and dilution by hydrogen on the yield of product has been examined for the example of the synthesis of 2-methylimidazole from ethylenediamine and acetic acid, and the stability of the catalyst in continuous reaction cycles with intermediate oxidative regeneration has been studied. The composition of the accompanying products has been established and a mechanism proposed for their formation.N. D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, Moscow 117913. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 4, pp. 932–940, April, 1992.     

Energy dispersive X-ray fluorescence analysis of chloride in reforming catalysts

A relatively less expensive Phillips PV 9500/SY 585 automatic energy dispersive X-ray fluorescence (EDXFR) spectrometer with rhodium target, was modified using a commercial kitchen aluminium wrapping foil filter, for the determination of chloride in bifunctional reforming catalysts. Quantitation of chloride was carried out by the Claisse-Quintin method with a catalyst sample of known chloride content as an external standard. The results of EDXRF chloride analysis of different catalyst samples, containing varying amounts of percent carbon and chloride, compared well (p>0.75) with those obtained by silver chloride precipitation method. The small values of percent relative standard deviations at 0.4 to 4.5% showed a good reproducibility of the method. With the total analysis time of a few minutes combined with no sample preparation, the present method seems to be superior as compared to presently employed methods of chloride analysis in reforming catalysts.     

Thermal analysis and high-temperature X-ray diffraction study of BiNbO4

Journal of Thermal Analysis and Calorimetry - Phase transformations of bismuth orthoniobate BiNbO4 were studied by the methods of differential scanning calorimetry and high-temperature X-ray...     

Thermal analysis and high-temperature X-ray diffraction of nano-tricalcium phosphate crystallization

Calcium phosphate biomaterials have long ago attracted the interest of world-wide scientists because they form the main inorganic constituent of the human bones and teeth. Classical approaches to synthesize this ceramic material did not give satisfactory results until present, so new approaches are required. In this article the tricalcium phosphate achievement by a method which is a combination of sol–gel and classic precipitation from solution is presented, starting from CaCl₂ as calcium precursor and H₃PO₄ as phosphorus precursor, without pH adjustment. The reaction mixture was allowed to maturate for 2 months, the time influence on the precipitated material being presented in previous articles. Present studies aimed at the influence of temperature on the structural characteristics of precipitated and maturated material, by means of thermal analysis, X-ray diffraction, infrared spectroscopy, and high-temperature X-ray diffraction. A complex type thermal decomposition takes place while heating the sample to 1000 °C, with superposed and parallel processes. The sample goes through alternative amorphous and crystalline stages before final crystallization of β-tricalcium phosphate takes place. The high-temperature XRD studies offered the great advantage of being both a synthesis and a physico-chemical characterization technique, which along with thermal analysis and infrared spectroscopy, gave a lot of useful information in a very short time.     

X-ray studies of supported copper-aluminium catalysts

Structural peculiarities of the formation of copper-aluminium catalysts at copper concentrations <10 wt% and calcination temperatures of 573–1173 K have been studied.

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<10% . 573–1173°K.

     

X-ray diffraction studies of mesomorphic ferrocene diesters

Abstract

The crystal and molecular structure of 1,l ′-bis(4′-pentyloxybiphenyl)ferrocene dicarboxylate ester (1) has been determined by X-ray diffraction at 295 and 160K. The molecule is found to exist at both temperatures in an extended S geometry. The carboxyl groups are essentially coplanar with the cyclopentadienyl rings but almost perpendicular to the attached phenyl ring. Low angle X-ray diffraction of three diesters in the smectic phases were also studied. The results were not very definitive because of the lack of thermal stability for the monotropic phase behaviour. Nevertheless, the layer spacing of about 47 A for one of the compounds at 409K is consistent with the extended S shape conformation.     

Preparation and X-ray diffraction studies of curium hydrides

Curium hydrides were prepared by reaction of curium-248 metal with hydrogen and characterized by X-ray powder diffraction. Several of the syntheses resulted in a hexagonal compound with average lattice parameters of a₀ = 0.3769(8) nm and c₀ = 0.6732(12) nm. These products are considered to be CmH_3?δ by analogy with the behavior of lanthanide-hydrogen and lighter actinide-hydrogen systems. Face-centered cubic products with an average lattice parameter of a₀ = 0.5322(4) nm were obtained from other curium hydride preparations. This parameter is slightly smaller than that reported previously for cubic curium dihydride, CmH_2+x (B. M. Bansal and D. Damien, Inorg. Nucl. Chem. Lett., 6, 603, 1970). The present results established a continuation of typical heavy trivalent lanthanide-like behavior of the transuranium actinide-hydrogen systems through curium.     

X-ray diffraction and solid-state NMR studies of a germanium binuclear complex

A compound formulated as (C4H12N2)[Ge2(pmida)2(OH)2] x 4 H2O (where pmida(4-) = N-(phosphonomethyl)iminodiacetate and C4H12N2(2+) = piperazinedium cation), containing the anionic [Ge2(pmida)2(OH)2]2- complex, has been synthesised by the hydrothermal approach and its structure determined by single-crystal X-ray diffraction analysis. Several high-resolution solid-state magic-angle spinning (MAS) NMR techniques, in particular two-dimensional 1H-X(13C,31P) heteronuclear correlation (HETCOR) and 1H-1H homonuclear correlation (HOMCOR) experiments incorporating a frequency-switched Lee-Goldburg (FS-LG) decoupling scheme, have been employed for the first time in such a material. Using these tools in tandem affords an excellent general approach to study the structure of other inorganic-organic hybrids. We assigned the NMR resonances with the help of C...H and P...H internuclear distances obtained through systematic statistical analyses of the crystallographic data. The compound was further characterised by powder X-ray diffraction techniques, IR and Raman spectroscopy, and by elemental and thermal analyses (thermogravimetric analysis and differential scanning calorimetry).     

Investigation of supported nickel catalysts by X-ray absorption spectrometry and X-ray diffraction using synchrotron radiation

In a previous paper a study of the supported nickel catalysts based on extended X-ray absorption fine structure spectroscopy was presented for analysis of the first coordination shell. The present study evidenced a strong deformation of the local structure of the metal due to its interaction with oxide support. The average particle size, microstrains and probability of faults, the particle size distribution function of supported Ni catalysts were determined by X-ray diffraction method. The method is based on Fourier analysis of experimental X-ray line profile (1 1 1), (2 0 0) and (2 2 0). The global structure is obtained with a fitting method based on the generalized Fermi function facilities for approximation. A chemisorption model was elaborated by correlation of the local and global structure connected with the specific surface areas. The results obtained on supported Ni catalysts which are used in H/D isotopic exchange reactions are reported. Both types of measurements were performed on the Beijing synchrotron radiation facilities.     

In situ high-temperature X-ray diffraction,FT-IR and thermal analysis studies of the reaction between natural hydroxyapatite and aluminum powder

Journal of Thermal Analysis and Calorimetry - The present work focuses on the study of the effects of mechanical activation on the reaction between hydroxyapatite (HAp) and aluminum metal powder...