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101.
Indium on silica, alumina and zeolite chabazite (CHA), with a range of In/Al ratios and Si/Al ratios, have been investigated to understand the effect of the support on indium speciation and its corresponding influence on propane dehydrogenation (PDH). It is found that In2O3 is formed on the external surface of the zeolite crystal after the addition of In(NO3)3 to H-CHA by incipient wetness impregnation and calcination. Upon reduction in H2 gas (550 °C), indium displaces the proton in Brønsted acid sites (BASs), forming extra-framework In+ species (In-CHA). A stoichiometric ratio of 1.5 of formed H2O to consumed H2 during H2 pulsed reduction experiments confirms the indium oxidation state of +1. The reduced indium is different from the indium species observed on samples of 10In/SiO2, 10In/Al2O3 (i.e., 10 wt% indium) and bulk In2O3, in which In2O3 was reduced to In(0), as determined from the X-ray diffraction patterns of the product, H2 temperature-programmed reduction (H2-TPR) profiles, pulse reactor investigations and in situ transmission FTIR spectroscopy. The BASs in H-CHA facilitate the formation and stabilization of In+ cations in extra-framework positions, and prevent the deep reduction of In2O3 to In(0). In+ cations in the CHA zeolite can be oxidized with O2 to form indium oxide species and can be reduced again with H2 quantitatively. At comparable conversion, In-CHA shows better stability and C3H6 selectivity (∼85%) than In2O3, 10In/SiO2 and 10In/Al2O3, consistent with a low C3H8 dehydrogenation activation energy (94.3 kJ mol−1) and high C3H8 cracking activation energy (206 kJ mol−1) in the In-CHA catalyst. A high Si/Al ratio in CHA seems beneficial for PDH by decreasing the fraction of CHA cages containing multiple In+ cations. Other small-pore zeolite-stabilized metal cation sites could form highly stable and selective catalysts for this and facilitate other alkane dehydrogenation reactions.Indium-containing chabazite zeolites show better stability and C3H6 selectivity for propane dehydrogenation than In2O3, In/SiO2 and In/Al2O3. Extra-framework In+ is identified as the stable active site upon reduction of an impregnated sample. 相似文献
102.
Jaan Aarik Aleks Aidla Arvo Kikas Tanel Kmbre Raul Rammula Peeter Ritslaid Teet Uustare Vino Sammelselg 《Applied Surface Science》2004,230(1-4):292-300
Atomic layer deposition of hafnium dioxide (HfO2) on silicon substrates was studied. It was revealed that due to low adsorption probability of HfCl4 on silicon substrates at higher temperatures (450–600 °C) the growth was non-uniform and markedly hindered in the initial stage of the HfCl4–H2O process. In the HfI4–H2O and HfI4–O2 processes, uniform growth with acceptable rate was obtained from the beginning of deposition. As a result, the HfI4–H2O and HfI4–O2 processes allowed deposition of smoother, more homogeneous and denser films than the HfCl4–H2O process did. The crystal structure developed, however, faster at the beginning of the HfCl4–H2O process. 相似文献
103.
Agnieszka Andrykiewicz Luis Patino Jose Raul Naranjo Matthias Witte Marie-Claude Hepp-Reymond Rumyana Kristeva 《BMC neuroscience》2007,8(1):101
Background
Over the last few years much research has been devoted to investigating the synchronization between cortical motor and muscular activity as measured by EEG/MEG-EMG coherence. The main focus so far has been on corticomuscular coherence (CMC) during static force condition, for which coherence in beta-range has been described. In contrast, we showed in a recent study [1] that dynamic force condition is accompanied by gamma-range CMC. The modulation of the CMC by various dynamic force amplitudes, however, remained uninvestigated. The present study addresses this question. We examined eight healthy human subjects. EEG and surface EMG were recorded simultaneously. The visuomotor task consisted in isometric compensation for 3 forces (static, small and large dynamic) generated by a manipulandum. The CMC, the cortical EEG spectral power (SP), the EMG SP and the errors in motor performance (as the difference between target and exerted force) were analyzed. 相似文献104.
Michaeleen R. Munrow Ranga Subramanian Andrea J. Minei Matthew K. MacLeod Raul Crespo Mitsuaki Izuha Yoshio Tatamitani Kenji Yamanou Stewart E. Novick 《Journal of Molecular Spectroscopy》2007,242(2):129-138
The microwave spectra of the gauche conformer of perfluoro-n-butane, n-C4F10, of perfluoro-iso-butane, (CF3)3CF, and of tris(trifluoromethyl)methane, (CF3)3CH, have been observed and assigned. The rotational and centrifugal distortion constants for gauche n-C4F10 are: A = 1058.11750(7) MHz, B = 617.6832(1) MHz, C = 552.18794(1) MHz, ΔJ = 0.0257(5) kHz, δJ = 0.0052(3) kHz. A C-C-C-C dihedral angle, ω, of ∼55° has been determined. These values agree well with those obtained from a coupled cluster (CCSD/cc-PVTZ) calculation. The rotational and centrifugal distortion constants for iso-C4F10 and iso-C4HF9 are: Bo = 816.4519(4) MHz, DJ = 0.023(2) kHz, and Bo = 903.6985(25) MHz, DJ = 0.043(4) kHz, respectively. The dipole moment of iso-C4F10 and iso-C4HF9 have been measured and found to be 0.0338(8) and 1.69(9) D, respectively. 相似文献
105.
Raul Quiroga-Barranco 《Comptes Rendus Mathematique》2005,341(6):361-364
Let G be a connected noncompact simple Lie group acting isometrically on a connected compact pseudoRiemannian manifold M. Denote with and the dimension of the maximal null subspaces tangent to G and M, respectively. Then we always have . Our main result states that, if , then the G-action is, up to a finite covering, an algebraic action. We use this to obtain a complete characterization of a large family of G-actions, thus providing a partial positive answer to the conjecture proposed in Zimmer's program for pseudoRiemannian manifolds. To cite this article: R. Quiroga-Barranco, C. R. Acad. Sci. Paris, Ser. I 341 (2005). 相似文献
106.
107.
Raul R. Hunziker 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》1960,11(6):504-508
Résumé Les valeurs de contour de la solution d'un problème mixte harmonique sur l'arc portant des données deNeumann sont obtenus par une représentation conforme et par évaluation d'une intégrale généralisée. Cette méthode permet de calculer le minimum du coéfficient de trainée d'une aile supersonique.
The results presented in this paper were obtained in the course of research forConvair, A Division of General Dynamics Corporation, San Diego, Calif. 相似文献
The results presented in this paper were obtained in the course of research forConvair, A Division of General Dynamics Corporation, San Diego, Calif. 相似文献
108.
Calderon Morales R Tambyrajah V Jenkins PR Davies DL Abbott AP 《Chemical communications (Cambridge, England)》2004,(2):158-159
The Fischer indole synthesis occurs in high yield with one equivalent of the ionic liquid choline chloride[middle dot]2ZnCl(2); exclusive formation of 2,3-disubstituted indoles is observed in the reaction of alkyl methyl ketones, and the products readily sublime directly from the ionic liquid. 相似文献
109.
Olivera R SanMartin R Churruca F Domínguez E 《The Journal of organic chemistry》2002,67(21):7215-7225
A concise synthesis of a series of novel dibenzoxepino[4,5-d]pyrazoles was accomplished by implementation of an intramolecular Ullmann-ether reaction on o,o'-halohydroxy-4,5-diarylpyrazoles mediated by CuBr.DMS. An alternative useful approach based on the palladium-catalyzed biaryl-ether linkage formation (Buchwald-Hartwig reaction) was also successfully applied, offering limitations with regard to the steric demand of the substituents. The synthesis of the key o,o'-halohydroxy-4,5-diarylpyrazole intermediates proceeds through the construction of the heterocyclic ring by a tandem amine-exchange/heterocyclization sequence of 3-N,N-(dimethylamino)-1,2-diarylpropenones with phenylhydrazine followed by basic hydrolysis for deprotection. The enamino ketone precursors were conveniently prepared from the corresponding O-sulfonyloxy and O-benzoyloxy ortho-substituted 1,2-diarylethanones, starting from inexpensive salicylaldehyde or phenylacetic derivatives. Preliminary binding affinity experiments against peripheral and central nervous system receptors have been done with negative results. 相似文献
110.