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排序方式: 共有157条查询结果,搜索用时 171 毫秒
131.
J. A. Wang A. Cuan J. Salmones N. Nava S. Castillo M. Morn-Pineda F. Rojas 《Applied Surface Science》2004,230(1-4):94-105
The textural properties, morphological features, surface basicity and oxygen reduction behaviours of titania and Pt supported titania catalysts synthesized via a sol–gel method were studied by means of N2 physisorption, SEM, TEM, CO2-TPD and H2-TPR techniques. Mesostructured TiO2 shows a very narrow pore size distribution that uniformly centred at about 4 nm. High resolution TEM images confirmed that most of Pt particles on Pt/TiO2-SG had a size smaller than 2 nm. Both the titania support and Pt loaded catalysts chiefly contained weak basic sites with small amount of strong basic sites. Loading Pt did not significantly alter the surface reduction characters of titania, indicating a weak interaction between Pt metals and titania support. Catalytic evaluation revealed that the selectivity of NO reduction over titania was insensitive to variation of textural property. On the bare titania, low NO conversion but high selectivity to N2O was obtained. However, the Pt/TiO2-SG catalysts exhibited high NO conversion and high selectivity to N2, which is assumed to relate to NO dissociation catalysed by the metallic Pt clusters. In addition, when the reaction temperature was above 200 °C, 3–11% NO2 was yielded over the Pt/TiO2-SG catalysts, which was discussed on a basis of reaction competition, metal-support interaction and NO dissociation. 相似文献
132.
Mauro F. La Russa Silvestro A. Ruffolo Cristina M. Belfiore Valeria Comite Antonella Casoli Michela Berzioli Gianluca Nava 《Applied Physics A: Materials Science & Processing》2014,114(3):733-740
During the last restoration of the six paintings by Raffaele Rinaldi (1851–1916), located in the church of Maria SS. Annunziata (Marano Principato, Cosenza, Italy), made between 1890 and 1903, several scientific investigations were carried out on them. The present work aims at classifying the painting in terms of its materials and technical particularities. The goal of this study was to characterise the painting technique of the painter, its evolution and possible additions made during previous restorations. Pigments, binder media and raw materials used for the application of the ground and the paint layers were studied using electronic microscopy equipped with energy dispersive spectroscopy qualitative microanalysis (SEM-EDS), infrared spectroscopy (FTIR) and gas chromatography coupled with mass spectrometry (GC/MS). Furthermore, a complete analysis of the state of preservation of these paintings represents a scientific aid and guide for its restoration, taking into account the severe damage not exclusively due to natural decay processes. Our data can provide information about historical and stylistic background as well as advise for correct planning of the cleaning procedures. The identification of materials allowed a correct restoration. 相似文献
133.
Andrea Nava Dr. Luca Rigamonti Prof. Ennio Zangrando Prof. Roberta Sessoli Dr. Wolfgang Wernsdorfer Prof. Andrea Cornia 《Angewandte Chemie (International ed. in English)》2015,54(30):8777-8782
Tetrairon(III) single‐molecule magnets [Fe4(pPy)2(dpm)6] ( 1 ) (H3pPy=2‐(hydroxymethyl)‐2‐(pyridin‐4‐yl)propane‐1,3‐diol, Hdpm=dipivaloylmethane) have been deliberately organized into supramolecular chains by reaction with RuIIRuII or RuIIRuIII paddlewheel complexes. The products [Fe4(pPy)2(dpm)6][Ru2(OAc)4](BF4)x with x=0 ( 2 a ) or x=1 ( 2 b ) differ in the electron count on the paramagnetic diruthenium bridges and display hysteresis loops of substantially different shape. Owing to their large easy‐plane anisotropy, the s=1 diruthenium(II,II) units in 2 a act as effective seff=0 spins and lead to negligible intrachain communication. By contrast, the mixed‐valent bridges (s=3/2, seff=1/2) in 2 b introduce a significant exchange bias, with concomitant enhancement of the remnant magnetization. Our results suggest the possibility to use electron transfer to tune intermolecular communication in redox‐responsive arrays of SMMs. 相似文献
134.
During the course of years, various activities have been carried out at CESI (incorporating now former CISE Innovative Technologies labs) on Doppler wind lidar (DWL) for spaceborne applications. Historically, the first activities were related to the development of a CO2 laser transmitter for the DWL development with coherent (heterodyne) detection technique. More recently, efforts have been directed to the technology of neodymium solid-state laser transmitter with direct detection (edge technique). Presently, a work in course involves a team of European firms including CESI and is devoted to the breadboarding of a diode-pumped UV laser for DWL application. 相似文献
135.
Stephane Parola Roland Khem David Cornu Zian Kighelman Dragan Damjanovic Nava Setter 《Journal of Sol-Gel Science and Technology》2003,26(1-3):1109-1112
Pyrochlore free Pb(Mg1/3Nb2/3)O3 (PMN) thin films were prepared from mixed-metal precursors solutions using the sol-gel process. Lead acetate [Pb(CH3COO)2], magnesium acetate [Mg(CH3COO)2] and niobium ethoxide [Nb(C2H5O)5] were used as starting materials, while 2-isopropoxy-ethanol was chosen as solvent. The reactivity of the precursors was investigated in order to understand and control the process and thus to prevent the contamination of the PMN with the pyrochlore phase. The solution was spin-coated on TiO2/Pt/TiO2/SiO2/Si substrate. The thin films were characterized by SEM and XRD while dielectric measurements were performed on the bulk ceramic. 相似文献
136.
N. Nava P. Salas M. E. Llanos H. Pérez-Pastenes T. Viveros 《Hyperfine Interactions》2005,161(1-4):11-19
Alumina–europia mixed oxides with 5 and 10 wt.% Eu2O3 were studied by Mössbauer spectroscopy, 27Al MAS-NMR and X-ray diffraction (XRD). The samples were prepared by the sol–gel technique. The XRD patterns for the calcined samples show a broad peak around 2θ = 30° which is assigned to the Eu2O3; after treatment with hydrogen at 1073 K no reduction to Eu+2 or Eu0 was observed. The NMR spectra show three peaks, which are assigned to the octahedral, pentahedral and tetrahedral aluminum sites; the intensity of each peak depends on the concentration of europium ions. The Mössbauer spectra of the calcined samples show a single peak near zero velocity which is attributed to the Eu+3; after H2 treatment at 1073 K similar spectra were obtained, suggesting Eu+3 is not reducibly at this temperature. 相似文献
137.
Miguel A. Hernández Balboa Velia Vela Arévalo Victor H. Abrego Reyes Ana M. Velázquez A. Ganem-Quintanar David Quintanar Brígida Camacho Guadalupe Nava Arzaluz M. Rosales-Hoz Marco A. Leyva Enrique Angeles 《Chromatographia》2008,67(1-2):193-196
The results of CE studies of solid inclusion complexes of chlorambucil (CHL) and trimethyl-β-cyclodextrin (TM-β-CD) are presented.
Chlorambucil has low stability in aqueous solution, so the formation of complexes with β-CD is a good way to improve its stability
and dissolution. The experimental results confirm the existence of inclusion complexes. CE can differentiate free CHL from
CHL–TM-β-CD complexes due to their different electrophoretic mobilities. 相似文献
138.
Pellegrino S Contini A Clerici F Gori A Nava D Gelmi ML 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(28):8705-8715
A very efficient synthesis of orthogonally protected 1H-azepine-4-amino-4-carboxylic acid, abbreviated as Azn, a conformationally restricted analogue of ornithine, was realized. It was obtained on a gram scale in good overall yield in five steps, three of which did not require isolation of the intermediates, starting from the readily available 1-amino-4-oxo-cyclohexane-4-carboxylic acid. Both enantiomers were used for the preparation of pentapeptide models containing Ala, Aib, and Azn. Conformational studies using both spectroscopic techniques (NMR, CD) and molecular dynamics on model 5-mer peptides showed that the (R)-Azn isomer possesses a marked helicogenic effect. 相似文献
139.
M. García Hernández F. de J. Carrillo Romo A. García Murillo D. Jaramillo Vigueras M. A. Meneses Nava P. Bartolo Pérez G. Chadeyron 《Journal of Sol-Gel Science and Technology》2010,53(2):246-254
Erbium (Er3+) 0.5% mol doped barium titanate (BaTiO3) thin films were elaborated via sol–gel method and dip-coating technique using titanium alkoxide and barium pentanedionate.
Two syntheses were performed [with and without polyvinylpyrrolidone (PVP)] in order to obtain thick films. The BaTiO3:Er3+ thin films prepared from the sol with PVP were elaborated with 1 layer and those without PVP and were elaborated with 17 layers. In both cases, the films
were deposited on silica quartz substrates. Both BaTiO3:Er3+ films presented a cubic phase, as determined by X-ray diffraction. BaTiO3:Er3+ films elaborated with PVP via single-step dip coating produced crack-free films with thicknesses of ~800 nm. SEM micrographs
for the obtained BaTiO3:Er3+ films revealed high homogeneity and density. Mapping images obtained from BaTiO3:Er3+ revealed homogeneous distribution of Er3+ ions on the surface. XPS analyses of the chemical state and chemical environment of the constituent elements in the compositions
showed that Er3+ ions in (Ba1−x
Er
x
)TiO3 are in mixed valence of Er3+/Er2+. The BaTiO3:Er3+-PVP film exhibited luminescent properties under near-infrared excitation, as revealed by green emissions. The BaTiO3:Er3+-PVP film has good potential for optical applications. 相似文献
140.
[reaction: see text] An original TiCl(4)/t-BuNH(2)-mediated hydroamination/annulation domino reaction of delta-keto-acetylenes is described. The synthesis of pyrrolo[1,2-a]indole-2-carbaldehydes, starting from 2-carbonyl-1-propargyl-1H-indoles runs under mild reaction conditions. A conceivable mechanism is also discussed. TiCl(4) has proved to be an effective multiactivity reagent: catalyst/Lewis acid/water scavenger. Some unpublished 2-carbonyl-1-propargyl-1H-indoles are prepared by means of Suzuki- and Negishi-type reactions. 相似文献