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231.
CO Hydrogenation on Cobalt‐Based Catalysts: Tin Poisoning Unravels CO in Hollow Sites as a Main Surface Intermediate
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Dr. Anaëlle Paredes‐Nunez Davide Lorito Dr. Laurence Burel Dr. Debora Motta‐Meira Dr. Giovanni Agostini Nolven Guilhaume Dr. Yves Schuurman Dr. Frederic Meunier 《Angewandte Chemie (International ed. in English)》2018,57(2):547-550
Site poisoning is a powerful method to unravel the nature of active sites or reaction intermediates. The nature of the intermediates involved in the hydrogenation of CO was unraveled by poisoning alumina‐supported cobalt catalysts with various concentrations of tin. The rate of formation of the main reaction products (methane and propylene) was found to be proportional to the concentration of multi‐bonded CO, likely located in hollow sites. The specific rate of decomposition of these species was sufficient to account for the formation of the main products. These hollow‐CO are proposed to be main reaction intermediates in the hydrogenation of CO under the reaction conditions used here, while linear CO are mostly spectators. 相似文献
232.
Chao Cai Kang Liu Long Zhang Fangbiao Li Yao Tan Pengcheng Li Yanqiu Wang Maoyu Wang Zhenxing Feng Debora Motta Meira Wenqiang Qu Andrei Stefancu Wenzhang Li Hongmei Li Junwei Fu Hui Wang Dengsong Zhang Emiliano Cortés Min Liu 《Angewandte Chemie (International ed. in English)》2023,62(26):e202300873
The slow water dissociation process in alkaline electrolyte severely limits the kinetics of HER. The orientation of H2O is well known to affect the dissociation process, but H2O orientation is hard to control because of its random distribution. Herein, an atomically asymmetric local electric field was designed by IrRu dizygotic single-atom sites (IrRu DSACs) to tune the H2O adsorption configuration and orientation, thus optimizing its dissociation process. The electric field intensity of IrRu DSACs is over 4.00×1010 N/C. The ab initio molecular dynamics simulations combined with in situ Raman spectroscopy analysis on the adsorption behavior of H2O show that the M−H bond length (M=active site) is shortened at the interface due to the strong local electric field gradient and the optimized water orientation promotes the dissociation process of interfacial water. This work provides a new way to explore the role of single atomic sites in alkaline hydrogen evolution reaction. 相似文献
233.
Otaciro R. Nascimento Claudio J. Magon Jose Fernando Lima Jose Pedro Donoso Eglantina Benavente Jaime Paez Vladimir Lavayen Maria Angelica Santa Ana Guillermo Gonzalez 《Journal of Sol-Gel Science and Technology》2008,45(2):195-204
In this work we report results from continuous-wave (CW) and pulsed electron paramagnetic resonance (EPR) and proton nuclear
magnetic resonance (NMR) studies of the vanadium pentoxide xerogel V2O5:nH2O (n ≈ 1.6). The low temperature CW-EPR spectrum shows hyperfine structure due to coupling of unpaired V4+ electron with the vanadium nucleus. The analysis of the spin Hamiltonian parameters suggests that the V4+ ions are located in tetragonally distorted octahedral sites. The transition temperature from the rigid-lattice low-temperature
regime to the high temperature liquid-like regime was determined from the analysis of the temperature dependence of the hyperfine
splitting and the V4+ motional correlation time. The Electron Spin Echo Envelope Modulation (ESEEM) data shows the signals resulting from the interaction
of 1H nuclei with V4+ ions. The modulation effect was observed only for field values in the center of the EPR absorption spectrum corresponding
to the single crystals orientated perpendicular to the magnetic field direction. At least three protons are identified in
the xerogel by our magnetic resonance experiments: (I) the OH groups in the equatorial plane, (ii) the bound water molecules
in the axial V=O bond and (iii) the free mobile water molecules between the oxide layers. Proton NMR lineshapes and spin-lattice
relaxation times were measured in the temperature range between 150 K and 323 K. Our analysis indicates that only a fraction
of the xerogel protons contribute to the measured conductivity. 相似文献
234.
Antonio Evidente Alessio Cimmino Maurizio Vurro Charles L. Cantrell Andrea Motta 《Tetrahedron》2008,64(8):1612-1619
Phyllosticta cirsii, a fungal pathogen isolated from Cirsium arvense and proposed as biocontrol agent of this noxious perennial weed, produces in liquid cultures different phytotoxic metabolites with potential herbicidal activity. Four new oxazatricycloalkenones, named phyllostictines A-D, were isolated and characterized using essentially spectroscopic and chemical methods. Tested by leaf-puncture assay on the fungal host plant phyllostictine A proved to be highly toxic. The phytotoxicity decreases when both the dimension and the conformational freedom of the macrocyclic ring change, as in phyllostictines B and D, and it is totally lost when also the functionalization of the same ring is modified, as in phyllostictine C. Beside its phytotoxic properties, phyllostictine A has no antifungal activity, an interesting antibiotic activity only against Gram+ bacteria, and a noticeable zootoxic activity when tested at high concentrations. The integrity of the oxazatricycloalkenone system appears to be an important feature to preserve these activities. 相似文献
235.
Servoli E Maniglio D Aguilar MR Motta A San Roman J Belfiore LA Migliaresi C 《Macromolecular bioscience》2008,8(12):1126-1134
Surface properties have a significant influence on the performance of biomedical devices. The influence of surface chemistry on the amount and distribution of adsorbed proteins has been evaluated by a combination of atomic force microscopy (AFM) and surface plasmon resonance (SPR). Adsorption of albumin, fibrinogen, and fibronectin was analyzed under static and dynamic conditions, employing self-assembled monolayers (SAMs) as model surfaces. AFM was performed in tapping mode with antibody-modified tips. Phase-contrast images showed protein distribution on SAMs and phase-shift entity provided information on protein conformation. SPR analysis revealed substrate-specific dynamics in each system investigated. When multi-protein solutions and diluted human plasma interacted with SAMs, SPR data suggested that surface chemistry governs the equilibrium composition of the protein layer. 相似文献
236.
V. Lavayen N. Mirabal M.A. Santa Ana C.M. Sotomayor Torres 《Applied Surface Science》2007,253(12):5185-5190
This work reports the successful realization of MoS2 nanotubes by a novel intercalation chemistry and hydrothermal treatment. An inorganic-organic precursor of hexadecylamine (HDA) and molybdenum disulphide (MoS2) were used in synthesizing the nanocomposite comprising laminar MoS2 with HDA intercalated in the interlaminar spacing. The formation of MoS2 nanotubes occurred during hydrothermal treatment (HT) by a self-organized rolling mechanism. The nanotubes were observed to have dimensions 2-12 m in length and inner diameters typically in the range of 25-100 nm. We also report the formation of amorphous nanocoils of MoS2 obtained during similar procedures. 相似文献
237.
Lucia Zetta Enrica Alberti Tiziano Motta Maurizio Canetti Fabio Bertini 《Journal of polymer science. Part A, Polymer chemistry》2007,45(20):4635-4646
Butadiene‐isoprene copolymerization with the system V(acac)3‐MAO was examined. Crystalline or amorphous copolymers were obtained depending on isoprene content. Both butadiene and isoprene units exhibit a trans‐1,4 structure and are statistically distributed along the polymer chain. Polymer microstructure, comonomer composition, and distribution along the polymer chain were determined by 13C and 1H NMR analysis. The thermal and X‐ray behaviors of the copolymers were also investigated and compared with results from solid‐state 13C NMR experiments. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4635–4646, 2007 相似文献
238.
P.M.A. de Farias B.S. Santos F.D. Menezes A.G. Brasil Jr. R. Ferreira M.A. Motta A.G. Castro-Neto A.A.S. Vieira D.C.N. Silva A. Fontes C.L. Cesar 《Applied Physics A: Materials Science & Processing》2007,89(4):957-961
Fluorescent semiconductor nanocrystals in quantum confinement regime (quantum dots) present several well-known features which
make them very useful tools for biological labeling purposes. Low photobleaching rates, high chemical stability and active
surface allowing conjugation to living cells explain the success of this labeling procedure over the commonly used fluorescent
dyes. In this paper we report the results obtained with highly fluorescent core–shell CdTe–CdS (diameter=3–7 nm) colloidal
nanocrystals synthesized in aqueous medium and conjugated to glucose molecules. The conjugated nanocrystals were incubated
with living yeast cells, in order to investigate their glucose up-take activity in real time, by confocal microscopy analysis.
PACS 87.83.+a; 61.46.Hk; 81.07.Ta 相似文献
239.
Catarina Motta de Moura Jaqueline Motta de Moura Jaqueline Pozzada dos Santos Roberta da Costa Kosinski Guilherme Luiz Dotto Luiz Antonio de Almeida Pinto 《Macromolecular Symposia》2012,319(1):240-245
Summary: Chitosan biofilms were prepared with and without plasticizer (glycerol and sorbitol). The physical and mechanical properties of chitosan biofilms with and without plasticizer were evaluated. Chitosan was obtained from shrimp wastes and characterized. The film forming solution (FFS) was obtained through chitosan dissolution and drying. The solution had its pH adjusted to 6.0 and oven dried (40 °C, 24 h) with forced air circulation. Chitosan biofilms without plasticizer showed a tensile strength about 36% higher than biofilms produced with plasticizer. On the other hand, biofilms with plasticizer presented superior values of elongation. The permeability of the water vapor and color presented significant difference (p < 0.05) between all biofilms. Chitosan/plasticizer biofilms showed higher values of water vapor permeability in relation to chitosan biofilms without plasticizer. 相似文献
240.
J. C. Motta Ferreira 《代数通讯》2013,41(9):3209-3216
In this article we prove that, if (U, ω) is a finite dimensional baric algebra of (γ, δ) type over a field F of characteristic ≠ 2,3,5 such that γ2 ? δ2 + δ = 1 and δ ≠ 0,1, then rad(U) = R(U) ∩ (bar(U))2, where R(U) is the nilradical (maximal nil ideal) of U. 相似文献