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排序方式: 共有103条查询结果,搜索用时 15 毫秒
21.
22.
Josette Olivier-Fourcade Manfred Womes Jean-Claude Jumas Fabienne Le Peltier Stéphane Morin Blaise Didillon 《Chemphyschem》2004,5(11):1734-1744
Alumina-supported Sn and PtSn particles are studied by 119Sn M?ssbauer spectroscopy after oxidation and reduction under various conditions. The observed species of Sn(IV), Sn(II) and Sn(0) are grouped in several categories, each being characterised by distinct structural properties. Tin phases in contact with the support or with platinum are identified. The results are used to establish a model describing the phase transformations occurring in PtSn particles under oxidising or reducing conditions. Particular attention is paid to the reduction/reoxidation mechanisms governing H2/O2 double titrations. An increased reactivity of tin towards oxygen, induced by the contact with platinum, is demonstrated. It is shown that tin contributes to the oxygen uptake VO1 of a first titration cycle by platinum-catalysed transformation of Sn(II) into an oxometallic phase Pt(x)Sn(O). The oxygen titre VO2 of a second cycle is due to O2 chemisorption on platinum only. 相似文献
23.
The ultraviolet spectra of six alkylchloramines are determined between 220 and 320 nm. The wavelengths of maximum absorption are 244 nm (? = 458 l mol?1 cm?1) for monochloramine, 252 nm (? = 372 l mol?1 cm?1) for methylchloramine, 251 nm (? = 378 l mol?1 cm?1) for ethylchloramine, 250 nm (? = 368 l mol?1 cm?1) for isopropylchloramine, 264 nm (? = 354 l mol?1 cm?1) for dimethylchloramine and 262 nm (? = 315 l mol?1 cm?1) for diethylchloramine. 相似文献
24.
Jean-Pierre Djukic Christophe Michon Michel Pfeffer Nathalie Kyritsakas-Gruber 《Journal of organometallic chemistry》2006,691(5):846-858
The heat-promoted reaction of 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene with cyclomanganated 2-[tricarbonyl(η6-phenyl)chromium]pyridine afforded, upon departure of a molecule of CO, a new stable manganese alkylidene complex in which, according to X-ray diffraction analyses, the heterocyclic ligand is anti-facial with respect to the Cr(CO)3 moiety. Similar heat-promoted reactions of unsymmetrically substituted diazoalkanes such as (Me3Si)(H)CN2, (Ph)(Me)CN2, (Ph)(t-Bu)CN2 and (Ph)(FcCH2CH2)CN2, which are precursors of more electrophilic alkylidenes, with cyclomanganated 2-[tricarbonyl(η6-phenyl)chromium]pyridine derivatives afforded new syn-facial heterobimetallic benzyl complexes. The stereoselectivity of these reactions depends on the steric demand of the substituents at the diazoalkane. A phenyl substituent at the diazoalkane favors the formation of syn-facial heterobimetallic benzyl complexes with the Ph group in the endo position. Combining this “phenyl directing effect” to the steric effect operated by a bulky group at the phenyldiazoalkane, like noticed with (Ph)(t-Bu)CN2, led to total stereoselectivity. This study discloses four new X-ray structures of syn-facial Cr,Mn benzyl complexes, which all present the same short Cr-to-Mn distance of ca. 3.04 Å. 相似文献
25.
Pyrolysis of spiro ((4-t-butyl cyclohexane)-1,2′-(4′,4′-dimethyl oxazolidine-3′ oxyl)) leads to spiro ((4-t-butyl cyclohexane)-1,2′-(4′,4′ oxazolidine 3′-hydroxy)) , 4-t-butyl cyclohexanone and 4-t-butyl cyclohexanoxime. Kinetic studies show that the reaction proceeds through an autocatalytic process. 相似文献
26.
Abdelmaula Aboulaich Manfred Womes Josette Olivier-Fourcade Patrick Willmann Jean-Claude Jumas 《Solid State Sciences》2010,12(1):65-72
The structural and textural properties of a Sn-0.4BPO4 composite material synthesized by ex situ dispersion of β-Sn in a BPO4 matrix were investigated by using several complementary techniques to study the global order (XRD, TGA-DSC, SEM-XEDS) and the local order (FT-IR, 119Sn Mössbauer spectroscopy and X-ray absorption spectroscopy). The results reveal that the composite material consists of three main components: an electrochemically active species “Sn”, an inactive matrix “BPO4”, and an amorphous Sn(II) borophosphate which acts as a link between the two former and which improves the cohesion of the composite. The electrochemical performances of the composite material were tested in Swagelok-type cells with metallic Li as counter-electrode. It shows a high reversible capacity of about 500 mAh g?1 at a C/20 rate, and a very good stability under cycling even at very fast rates of C or C/1.3. 相似文献
27.
Djukic JP Michon C Ratkovic Z Kyritsakas-Gruber N de Cian A Pfeffer M 《Dalton transactions (Cambridge, England : 2003)》2006,(12):1564-1573
The thermolytic coupling of Ph(2)CN(2) and (t-Bu)(Ph)CN(2) with doubly cyclomanganated 2,5-diphenylpyrazine and 4,6-diphenylpyrimidine afforded substantial amounts of new triple decker compounds of either C(i) and C(2) symmetry respectively containing, in both series, two eta(3)-bonded Mn(CO)(3) fragments which intervene as scaffolds sustaining the helical non-conjugated triaryl backbone. The molecular structures of two pyrazine derivatives show a typical non-parallel stacking of the aromatic rings and the encapsulation of the central pyrazyl fragment with interplanar centroid-to-centroid distances of ca. 3.5 A. The stacking of the aromatics in the triple-decker pyrimidine derivatives has been assessed by (1)H NMR experiments at low temperature. All the triple-decker-type compounds are electroactive. Pyrimidine triple-deckers can reversibly be electrochemically reduced to the corresponding anions. 相似文献
28.
Highly Reduced Species Mechanisms for iso‐Cetane Using the Local Self‐Similarity Tabulation Method
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We utilize the local self‐similarity tabulation method to drastically downsize the number of species involved in a detailed kinetic mechanism of iso‐cetane. Reduced‐species mechanisms of 20 and 15 species are constructed, out of the 1114 species involved in the detailed mechanism, with a focus on high‐pressure combustion. The performance of the two reduced mechanisms are compared to the detailed one for a lean (? = 0.5), stoichiometric (? = 1.0), and rich (? = 1.5) iso‐cetane/air mixture at initial temperatures of 900 and 1100 K and constant pressures of 20 and 40 bar. Good to very good agreement between the detailed kinetic mechanism and the two highly reduced species mechanisms are demonstrated. 相似文献
29.
The reduction of iodine by hydroxylamine within the [H+] range 3×10−1–3×10−4 mol.L−1 was first studied until completion of the reaction. In most cases, the concentration of iodine decreased monotonically. However, within a narrow range of reagent concentrations ([NH3OH+]0/[I2]0 ratio below 15, [H+] around 0.1 mol.L−1, and ionic strength around 0.1 mol.L−1), the [I2] and [I3−] vs. time curves showed 2 and 3 extrema, respectively. This peculiar phenomenon is discussed using a 4 reaction scheme (I2+I−⇔︁I3−, 2 I2+NH3OH++H2O→HNO2+4 I−+5 H+, NH3OH++HNO2→N2O+2 H2O+H+, and 2 HNO2+2 I−+2 H+→2 NO+I2+2 H2O). In a flow reactor, sustained oscillations in redox potential were recorded with an extremely long period (around 24 h). The kinetics of the reaction was then investigated in the starting conditions. The proposed rate equation points out a reinforcement of the inhibition by hydrogen ions when [H+] is above 4×10−2 mol.L−1 at 25°C. A mechanism based on ion-transfer reactions is postulated. It involves both NH2OH and NH3OH+ as the reducing reactive species. The additional rate suppression by H+ at low pH would be connected to the existence of H2OI+ in the reactive medium. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 785–797, 1998 相似文献
30.
Josette Olivier-Fourcade Claire Adenis Jean -Claude Jumas Etienne Philippot 《Hyperfine Interactions》1986,28(1-4):781-784
Iodine vapour transport, carried out in the In-Sn-S ternary system leads to single crystals with quite different morphologies: needles, sticks, sheets and polyhedra. The two oxidation states of tin atoms are shown for all these phases by119Sn Mössbauer effect. A varying relative proportion of tin(IV) — tin(II) is observed according to the different crystal forms. 相似文献