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61.
Henri-Joël Sedjame Rachid Brahmi Gwendoline Lafaye Jacques Barbier Céline Fontaine 《Comptes Rendus Chimie》2018,21(3-4):182-193
Monolithic catalysts are prepared by washcoating cordierite monoliths with different sols (Pt/Al2O3, Pt/CeO2, Pt/ZrO2, Pt/Al2O3CeO2, Pt/Al2O3ZrO2, and Pt/CeO2ZrO2). These sols are prepared by a sol–gel process and characterized by specific surface area (SBET), inductively coupled plasma, hydrogen chemisorption, high-resolution transmission electron microscopy, field emission scanning electron microscopy, oxygen storage capacity, X-ray diffraction, temperature-programmed reduction, CO2 chemisorption, and the model reaction of 3,3-dimethylbutene isomerization. The catalytic performances of the monolithic catalysts are then evaluated for the acetic acid oxidation. The nature of catalyst coating has been found to influence the adherence with the cordierite monolith and the presence of cerium in the catalyst appears to increase the adherence of the latter. Pt/CeO2, Pt/Al2O3CeO2, and Pt/CeO2ZrO2 are found to be the most reducible catalysts (oxygen storage capacity and temperature-programmed reduction) and to have the lowest acidities (3,3-dimethylbutene isomerization). CO2 chemisorption shows that these catalysts possess a good basicity. From the relation established between the catalytic activity and the redox and acid–base properties it has been concluded that the reducibility is the key factor for a good catalytic activity although the basicity has a significant influence on the catalytic performance. 相似文献
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Matmour R De Cat I George SJ Adriaens W Leclère P Bomans PH Sommerdijk NA Gielen JC Christianen PC Heldens JT van Hest JC Löwik DW De Feyter S Meijer EW Schenning AP 《Journal of the American Chemical Society》2008,130(44):14576-14583
Two oligo(p-phenylenevinylene)-peptide hybrid amphiphiles have been synthesized using solid- and liquid-phase strategies. The amphiliphiles are composed of a pi-conjugated oligo(p-phenylenevinylene) trimer (OPV) which is coupled at either a glycinyl-alanyl-glycinyl-alanyl-glycine (GAGAG) silk-inspired beta-sheet or a glycinyl-alanyl-asparagyl-prolyl-asparagy-alanyl-alanyl-glycine (GANPNAAG) beta-turn forming oligopeptide sequence. The solid-phase strategy enables one to use longer peptides if strong acidic conditions are avoided, whereas the solution-phase coupling gives better yields. The study of the two-dimensional (2D) self-assembly of OPV-GAGAG by scanning tunneling microscopy (STM) at the submolecular level demonstrated the formation of bilayers in which the molecules are lying antiparallel in a beta-sheet conformation. In the case of OPV-GANPNAAG self-assembled monolayers could not be observed. Absorption, fluorescence, and circular dichroism studies showed that OPV-GAGAG and OPV-GANPNAAG are aggregated in a variety of organic solvents. In water cryogenic temperature transmission electron microscopy (cryo-TEM), atomic force microscopy (AFM), light scattering, and optical studies reveal that self-assembled nanofibers are formed in which the helical organization of the OPV segments is dictated by the peptide sequence. 相似文献
64.
The mixture {yNH4Cl + (1 − y)MgCl2} (aq) has been studied using the hygrometric method at the temperature 298.15 K. The water activities are measured at total molalities from 0.30 mol kg−1 up to saturation for different ionic strength fractions y of NH4Cl with y = 0.20, 0.50 and 0.80. The obtained data allow the deduction of osmotic coefficients. Experimental results are compared with the calculations using the models of Zdanovskii–Stokes–Robinson, Kusik and Meissner, Robinson and Stokes, Lietzke and Stoughton, Reilly–Wood and Robinson and Pitzer. Thermodynamic properties have been modeled using the Pitzer ion-interaction model with inclusion of an ionic strength dependence of the third virial coefficient for the binary systems. From these measurements and the obtained binary parameters β(0), β(1), C(0) and C(1), the mixing ionic parameters θNH4Mg and ψNH4MgCl are determined by the standard Pitzer model. The results show that a good accuracy is obtained with the standard Pitzer model using extended binary parameters. The parameters θNH4Mg and ψNH4MgCl were used for evaluation of activity coefficients in the mixture. The excess Gibbs energy is also determined. 相似文献
65.
Sunto In questa Nota, si affronta il problema del comportamento asintotico nel tempo di perturbazioni alla quiete per il sistema
di equazioni per un fluido comprimibile, viscoso e politropico. Ammesso che esista una soluzione regolare globale, si dimostra,
sotto l’ipotesi che il gradiente della temperatura assegnata al bordo sia piccolo, che la differenza tra la soluzione corrispondente
a dati iniziali arbitrari e la quiete decade a zero pert che tende ad infinito nella normal diL
2.
The second author thanks the 60% contract MURST, also she acknowledges the GNFM of italian CNR-INDAM for financial supports. 相似文献
We consider the equation system for a compressible viscous polytropic fluid in a regualar bounded domain and we study the asymptotic behavior as time goes to infinity of perturbations with respect to the basic rest state. Under the assumption of the smallness of the gradient of the given temperature on the boundary, we prove the exponential decay of theL 2-norm of the difference between the solution corresponding to arbitrary initial data and the rest state.
The second author thanks the 60% contract MURST, also she acknowledges the GNFM of italian CNR-INDAM for financial supports. 相似文献
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69.
Rachid M'Hamdi Didier Thibaut Marcel Caude Eric Robert Catherine Grand 《Journal of separation science》1998,21(2):94-102
An optimization procedure is presented for group-type analysis of diesel fuel by supercritical fluid chromatography using packed silica column and a mixed mobile phase. A set of five responses, four values of resolution of a performance mixture and analysis time, was modeled using a Doehlert matrix for experimental design. Optimized experimental conditions for the five responses were obtained from a response surfaces optimization, taking into account various constraints on SF6 content in mobile phase and analysis time. The predicted and experimental resolutions were in good agreement for the different optimized conditions and one of them was selected to for application to a given diesel fuel for comparison with the results obtained by SFC using pure CO2 and by HPLC. The conditions found in this study provide an alternative method for the determination of mono-, di-, and polyaromatic compounds in middle distillates. 相似文献
70.
Thierry Schlama Rachid Baati Vronique Gouverneur Alain Valleix John R. Falck Charles Mioskowski 《Angewandte Chemie (International ed. in English)》1998,37(15):2085-2087
The total synthesis of the polyhalogenated antitumour agent halomon ( 1 ) was accomplished with two novel transformations as key steps: a Johnson–Claisen rearrangement of a dichlorinated alkene for the preparation of the tertiary chlorinated C3 and a new rearrangement of bromohydrins for the regiospecific introduction of the bromine and chlorine atoms on C6 and C7, respectively. 相似文献