The Experts below are selected from a list of 81 Experts worldwide ranked by ideXlab platform
Haiyan Liu - One of the best experts on this subject based on the ideXlab platform.
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Identification of acidic species in chloroaluminate ionic liquid catalysts
Journal of Catalysis, 2014Co-Authors: Jia Cui, Peter Anton August Klusener, Xianghai Meng, Rui Zhang, Zhichang Liu, Haiyan LiuAbstract:Abstract Chloroaluminate ionic liquids (ILs), especially composite ionic liquids (CILs) which are ILs modified with copper(I) chloride, are highly active and selective catalysts for the alkylation of 2-butene with isobutane. The Lewis and Bronsted acidic species of these ILs were investigated by NMR spectroscopy. Pyridine is found to be a suitable indicator. Lewis acidity arises mainly from Al2Cl7− having a chemical shift at 102 ppm in the 27Al NMR Spectrum, while Bronsted acidity arises from Al2Cl6OH− (chemical shift at 97 ppm). The peak at 94 ppm in the 27Al NMR Spectrum is related to Al2Cl5O−. These new insights have improved our understanding of the structure of the active species in chloroaluminate ionic liquid alkylation catalysts.
Helmut G. Alt - One of the best experts on this subject based on the ideXlab platform.
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Facile Synthesis of New Cationic Triphenylphosphine Derivatives and their Use for Propene Dimerization Reactions in Buffered Chloroaluminate Ionic Liquids
Advanced Synthesis & Catalysis, 2012Co-Authors: Matthias Dötterl, Peter Thoma, Helmut G. AltAbstract:We describe the facile synthesis of new, cationic triphenylphosphine derivatives containing para-trimethylammonium substituents. The ionic phosphines were successfully employed in nickel-catalyzed propene dimerization reactions in highly Lewis acidic chloroaluminate ionic liquids. Buffering of such liquids is achieved by an interaction of the Lewis basic phosphine with the Lewis acidic aluminum centers. The PAl interaction of triarylphosphines and tri-tert-butylphosphine with the highly acidic ionic liquid [1-butyl-3-methylimidazolium]+ [Al2Cl7]− was monitored by 31P and 27Al NMR spectroscopy. Coupling of tri-tert-butylphosphine with 27Al resulted in an expected but unusual sextet in the 31P NMR Spectrum and a doublet in the 27Al NMR Spectrum.
Piet J. Grobet - One of the best experts on this subject based on the ideXlab platform.
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Aluminium Coordinations in Zeolite Mordenite By 27Al Multiple Quantum MAS NMR Spectroscopy
European Journal of Inorganic Chemistry, 2000Co-Authors: Tie-hong Chen, Bh Wouters, Piet J. GrobetAbstract:27Al 3Q MAS NMR spectroscopy has been applied to study the coordination state of the species giving the 30 ppm Al NMR signal in the 27Al MAS NMR Spectrum of activated mordenite materials. From the 27Al 3Q MAS NMR measurements it is evident that the broad peak at 30 ppm in the 27Al NMR Spectrum of the mordenite calcined at temperatures up to 600 °C comes mainly from the distorted four-coordinated Al. By simulation a quadrupolar coupling constant of 5.8 MHz was estimated for the distorted tetrahedral Al. For samples calcined at 650 and 700 °C, a small amount of pentacoordinated Al emerges. The majority of the signal, however, arises from distorted tetrahedral Al. A two-step calcination results in a significant contribution of the pentacoordinated Al to the signal at 30 ppm. From the simulated line-shape, a quadrupole coupling constant of 6.2 MHz is obtained for the latter signal. These data show that during the calcination of the mordenite, the coordination environment at the Al centre gradually becomes distorted to give rise to the shoulder at 30 ppm. With the increase of the calcination temperature, pentacoordinated Al species form
Michael Paris - One of the best experts on this subject based on the ideXlab platform.
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the two aluminum sites in the 27Al mas NMR Spectrum of kaolinite accurate determination of isotropic chemical shifts and quadrupolar interaction parameters
American Mineralogist, 2014Co-Authors: Michael ParisAbstract:The problem of resolving the two aluminum sites in the 27Al NMR Spectrum of kaolinite has been unsuccessfully addressed for 30 years. A few years ago, it was shown that the two sites cannot be spectrally separated even by the use of high magnetic fields. Nevertheless, it is still possible to determine the NMR parameters of both sites. In this article, we present an alternative approach. We show that, at low magnetic field (7 T), the individual spinning sideband lineshapes of the outer satellite transitions are sensitive enough to differentiate information coming from the two aluminum sites. Thus, the isotropic chemical shift δ, the quadrupolar constant CQ, and asymmetry parameter ηQ of each site can be obtained by accurately fitting the full 27Al MAS Spectrum acquired at low magnetic field. In return, this approach requires a carefully acquired and post-treated 27Al Spectrum. It is concluded that the two sets of parameters (δ = 7.5 ppm, CQ = 3.4 MHz, ηQ = 0.8) and (δ = 8.0 ppm, CQ = 3.0 MHz, ηQ = 0.9) represent the best and the unique solution overall. Moreover, the accuracy of these experimental values is independently and fully supported by first-principles calculations of the electric field gradient. The approach presented in this article can be easily applied, not only to clays or aluminosilicate materials, but to any compounds where the NMR parameters of overlapping spectral lines have to be determined. This can also be extended to sites of unequal multiplicity and to other nuclei. Moreover, this methodology can be useful in the characterization of small structural changes occurring partly at one particular site. Indeed, when the NMR parameters are barely modified, the spectral signatures due to both affected and unaffected sites may strongly overlap, making the spectral resonances broad and badly resolved. In such a case, determining the isotropic chemical shift and the quadrupolar coupling parameters may help to exceed the simple qualitative analysis of structural changes by offering the possibility of discriminating between structural models via the experimental data.
Hamid Reza Khavasi - One of the best experts on this subject based on the ideXlab platform.
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Synthesis, characterization and single crystal structure determination of aluminum alkoxydisilanolates: precursors for silica–alumina composite
Applied Organometallic Chemistry, 2010Co-Authors: Mostafa M. Amini, Gholamhossein Mohammadnezhad, Mehdi Mirzaee, Hamid Reza KhavasiAbstract:Several novel aluminum alkoxydisilanolate complexes were prepared by reaction of triphenylsilanol with aluminum 2-methoxyethoxide, aluminum 2-ethoxyethoxide, aluminum sec-butoxide and aluminum iso-propoxide. All new complexes, [(Ph3SiO)2Al(OR)]2 [where R = CH2CH2OCH3 (1), CH2CH2OC2H5 (2), CH(CH3)CH2CH3 (3) and CH(CH3)2 (4)] were characterized by elemental analysis, mass spectrometry and infrared spectroscopy (IR), as well as 1H, 13C, 29Si and 27Al NMR spectroscopies. The solid-state structures of the representative compound 2 and 4 were also verified by single-crystal X-ray analyses. Complexes 2 and 4 are dimers having distorted trigonal bipyramidal and tetrahedral coordination at the aluminum center, respectively. The 27Al NMR Spectrum of compound 2 showed that the solid-state structure of the complex was not retained in solution, and tetracoordinated aluminum was found in solution in contrast to the pentacoordinated geometry in the solid state. The hydrothermal treatment of 1 and 4 at 200 °C and the subsequent calcination at 1000 °C resulted in the formation of alumina–silica composite (4SiO2·Al2O3) with γ-alumina in the silica matrix. Copyright © 2010 John Wiley & Sons, Ltd.
