共查询到20条相似文献,搜索用时 15 毫秒
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Zhang Weibin Wu Weidong Wang Xueming Cheng Xinlu Yan Dawei Shen Changle Peng Liping Wang Yuying Bai Li 《Surface and interface analysis : SIA》2013,45(8):1206-1210
In this paper, the electronic structures of NbO2 and Nb2O5 are theoretically and experimentally analyzed. The oxides in the samples are mainly consisted of NbO2 and NbO, whereas the outmost layer of the samples is NbO2. After exposure to air, the outermost layer on all niobium samples is Nb2O5. The photoelectrons from the first 2–4 Å contribute to the spectra, so the valence band structure of NbO2 and Nb2O5 can be confirmed from ultraviolet photoelectron spectroscopy (UPS). By comparing the UPS with density of state results, the electronic structure of NbO2 and Nb2O5 can be distinguished from each other, and then the electronic structure was deconvoluted into several electronic states. The agreement between experimental result and theory is, in the best case, satisfactory. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
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In Situ and Theoretical Studies for the Dissociation of Water on an Active Ni/CeO2 Catalyst: Importance of Strong Metal–Support Interactions for the Cleavage of O–H Bonds 下载免费PDF全文
Dr. Javier Carrasco Dr. David López‐Durán Dr. Zongyuan Liu Dr. Tomáš Duchoň Dr. Jaime Evans Dr. Sanjaya D. Senanayake Dr. Ethan J. Crumlin Prof. Dr. Vladimir Matolín Dr. José A. Rodríguez Dr. M. Verónica Ganduglia‐Pirovano 《Angewandte Chemie (International ed. in English)》2015,54(13):3917-3921
Water dissociation is crucial in many catalytic reactions on oxide‐supported transition‐metal catalysts. Supported by experimental and density‐functional theory results, the effect of the support on O? H bond cleavage activity is elucidated for nickel/ceria systems. Ambient‐pressure O 1s photoemission spectra at low Ni loadings on CeO2(111) reveal a substantially larger amount of OH groups as compared to the bare support. Computed activation energy barriers for water dissociation show an enhanced reactivity of Ni adatoms on CeO2(111) compared with pyramidal Ni4 particles with one Ni atom not in contact with the support, and extended Ni(111) surfaces. At the origin of this support effect is the ability of ceria to stabilize oxidized Ni2+ species by accommodating electrons in localized f‐states. The fast dissociation of water on Ni/CeO2 has a dramatic effect on the activity and stability of this system as a catalyst for the water‐gas shift and ethanol steam reforming reactions. 相似文献
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Timo Glaser Jannick Meinecke Dr. Christian Länger Jan-Niclas Luy Prof. Dr. Ralf Tonner Prof. Dr. Ulrich Koert Prof. Dr. Michael Dürr 《Chemphyschem》2021,22(4):404-409
The reaction of methyl enol ether functionalized cyclooctyne on the silicon (001) surface was investigated by means of X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT). Three different groups of final states were identified; all of them bind on Si(001) via the strained triple bond of cyclooctyne but they differ in the configuration of the methyl enol ether group. The majority of molecules adsorbs without additional reaction of the enol ether group; the relative contribution of this configuration to the total coverage depends on substrate temperature and coverage. Further configurations include enol ether groups which reacted on the silicon surface either via ether cleavage or enol ether groups which transformed on the surface into a carbonyl group. 相似文献
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M. Lampimäki K. Lahtonen M. Hirsimäki M. Valden 《Surface and interface analysis : SIA》2007,39(4):359-366
Initial surface oxidation and nanoscale morphology on Cu{100}, Cu(Ag) and Ag/Cu{100} have been investigated in situ by X‐ray photoelectron spectroscopy (XPS), X‐ray induced Auger electron spectroscopy (XAES) and the inelastic electron background analysis as a function of oxygen exposure at 3.7 × 10?2 and 213 mbar pressures at a surface temperature of 373 K. Relative Cu2O concentrations have been quantified by analysis of the peak shape of the XAES Cu LMM transition. The surface morphology of Cu2O islands and the Ag layer has been characterized by inelastic electron background analysis of XAES O KLL and Ag 3d transitions. Oxygen‐induced segregation of Cu, as well as the subsequent Cu2O island formation on Cu(Ag) and Ag/Cu{100} surfaces, has been investigated quantitatively. Our results indicate that Ag has a clear inhibitive effect on the initial oxidation and Cu2O island formation on Cu(Ag) and Ag/Cu{100} surfaces. The Cu2O islands are also observed to remain highly strained on Ag/Cu{100} even at higher O2 exposures. The results suggest that strained Cu2O islands eventually penetrate through the buried Ag layer, and in conjunction with segregating Cu atoms enable the oxidation to proceed at a similar rate to or even faster than on the unalloyed Cu surface. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
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Finazzi E Di Valentin C Pacchioni G Chiesa M Giamello E Gao H Lian J Risse T Freund HJ 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(14):4404-4414
The adsorption of small amounts of alkali metal atoms (Li, Na, K, Rb, and Cs) on the surface of MgO powders and thin films has been studied by means of EPR spectroscopy and DFT calculations. From a comparison of the measured and computed g values and hyperfine coupling constants (hfccs), a tentative assignment of the preferred adsorption sites is proposed. All atoms bind preferentially to surface oxide anions, but the location of these anions differs as a function of the deposition temperature and alkali metal. Lithium forms relatively strong bonds with MgO and can be stabilized at low temperatures on terrace sites. Potassium interacts very weakly with MgO and is stabilized only at specific sites, such as at reverse corners where it can interact simultaneously with three surface oxygen atoms (rubidium and cesium presumably behave in the same way). Sodium forms bonds of intermediate strength and could, in principle, populate more than a single site when deposited at room temperature. In all cases, large deviations of the hfccs from the gas-phase values are observed. These reductions in the hfccs are due to polarization effects and are not connected to ionization of the alkali metal, which would lead to the formation of an adsorbed cation and a trapped electron. In this respect, hydrogen atoms behave completely differently. Under similar conditions, they form (H(+))(e(-)) pairs. The reasons for this different behavior are discussed. 相似文献
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In Situ Observation of Surface Species on Iridium Oxide Nanoparticles during the Oxygen Evolution Reaction 下载免费PDF全文
Hernan G. Sanchez Casalongue Dr. May Ling Ng Dr. Sarp Kaya Dr. Daniel Friebel Dr. Hirohito Ogasawara Dr. Anders Nilsson 《Angewandte Chemie (International ed. in English)》2014,53(28):7169-7172
An iridium oxide nanoparticle electrocatalyst under oxygen evolution reaction conditions was probed in situ by ambient‐pressure X‐ray photoelectron spectroscopy. Under OER conditions, iridium undergoes a change in oxidation state from IrIV to IrV that takes place predominantly at the surface of the catalyst. The chemical change in iridium is coupled to a decrease in surface hydroxide, providing experimental evidence which strongly suggests that the oxygen evolution reaction on iridium oxide occurs through an OOH‐mediated deprotonation mechanism. 相似文献
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Emmanuelle Orhan Fenelon M Pontes Edson R Leite Paulo S Pizani José A Varela Elson Longo 《Chemphyschem》2005,6(8):1530-1536
Ultrafine PbZr0.20Ti0.80O3 was amorphized through high-energy mechanical milling. The structural evolution through the amorphization process was accompanied by various characterization techniques, such as X-ray diffraction, Fourier-transformed IR spectroscopy (FTIR), high-resolution transmission electron microscopy (HR-TEM), and Raman spectroscopy. A strong photoluminescence was measured at room temperature for amorphized PbZr0.20Ti0.80O3, and interpreted by means of high-level quantum mechanical calculations in the density functional theory framework. Three periodic models were used to represent the crystalline and amorphized PbZr0.20Ti0.80O3, and they allowed the calculation of electronic properties that are consistent with the experimental data and that explain the appearance of photoluminescence. 相似文献
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Laurent Mirolo Tobias Schmidt Dr. Sonja Eckhardt Prof. Dr. Markus Meuwly Prof. Dr. Katharina M. Fromm 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(5):1754-1761
Artificial implants and biomaterials lack the natural defense system of our body and, thus, have to be protected from bacterial adhesion and biofilm formation. In addition to the increasing number of implanted objects, the resistance of bacteria is also an important problem. Silver ions are well‐known for their antimicrobial properties, yet not a lot is known about their mode of action. Silver is expected to interact on many levels, thus the development of silver resistance is very difficult. Nevertheless, some bacteria are able to resist silver, even at higher concentrations. One such defense mechanism of bacteria against heavy‐metal intoxication includes an efflux system. SilE, a periplasmic silver‐binding protein that is involved in this defense mechanism, has been shown to possess numerous histidine functions, which strongly bind to silver atoms, as demonstrated by ourselves previously. Herein, we address the question of how histidine binds to silver ions as a function of pH value. This property is important because the local proton concentration in cells varies. Thus, we solved the crystal structures of histidine–silver complexes at different pH values and also investigated the influence of the amino‐acid configuration. These results were completed by DFT calculations on the binding strength and packing effects and led to the development of a model for the mode of action of SilE. 相似文献
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Dr. Wei Zhao Julian Gebhardt Florian Späth Karin Gotterbarm Christoph Gleichweit Prof. Dr. Hans‐Peter Steinrück Prof. Dr. Andreas Görling Dr. Christian Papp 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(8):3347-3358
Understanding the adsorption and reaction between hydrogen and graphene is of fundamental importance for developing graphene‐based concepts for hydrogen storage and for the chemical functionalization of graphene by hydrogenation. Recently, theoretical studies of single‐sided hydrogenated graphene, so called graphone, predicted it to be a promising semiconductor for applications in graphene‐based electronics. Here, we report on the synthesis of graphone bound to a Ni(111) surface. We investigate the formation process by X‐ray photoelectron spectroscopy (XPS), temperature‐programmed desorption (TPD), and density‐functional theory calculations, showing that the hydrogenation of graphene with atomic hydrogen indeed leads to graphone, that is, a hydrogen coverage of 1 ML (4.2 wt %). The dehydrogenation of graphone reveals complex desorption processes that are attributed to coverage‐dependent changes in the activation energies for the associative desorption of hydrogen as molecular H2. 相似文献
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Till Cremer Claudia Kolbeck Kevin R. J. Lovelock Dr. Natalia Paape René Wölfel Peter S. Schulz Dr. Peter Wasserscheid Prof. Dr. Henry Weber Jens Thar Barbara Kirchner Prof. Dr. Florian Maier Dr. Hans‐Peter Steinrück Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(30):9018-9033
Ten [C8C1Im]+ (1‐methyl‐3‐octylimidazolium)‐based ionic liquids with anions Cl?, Br?, I?, [NO3]?, [BF4]?, [TfO]?, [PF6]?, [Tf2N]?, [Pf2N]?, and [FAP]? (TfO=trifluoromethylsulfonate, Tf2N=bis(trifluoromethylsulfonyl)imide, Pf2N=bis(pentafluoroethylsulfonyl)imide, FAP=tris(pentafluoroethyl)trifluorophosphate) and two [C8C1C1Im]+ (1,2‐dimethyl‐3‐octylimidazolium)‐based ionic liquids with anions Br? and [Tf2N]? were investigated by using X‐ray photoelectron spectroscopy (XPS), NMR spectroscopy and theoretical calculations. While 1H NMR spectroscopy is found to probe very specifically the strongest hydrogen‐bond interaction between the hydrogen attached to the C2 position and the anion, a comparative XPS study provides first direct experimental evidence for cation–anion charge‐transfer phenomena in ionic liquids as a function of the ionic liquid’s anion. These charge‐transfer effects are found to be surprisingly similar for [C8C1Im]+ and [C8C1C1Im]+ salts of the same anion, which in combination with theoretical calculations leads to the conclusion that hydrogen bonding and charge transfer occur independently from each other, but are both more pronounced for small and more strongly coordinating anions, and are greatly reduced in the case of large and weakly coordinating anions. 相似文献
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Hibbs DE Austin-Woods CJ Platts JA Overgaard J Turner P 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(5):1075-1084
The experimental electron density distribution in taurine, 2-aminoethane sulfonic acid, 1, has been determined from high-resolution X-ray diffraction data collected at a temperature of 100 K. Taurine crystallizes as a zwitterion in the monoclinic space group P2(1)/c. Topological analysis of the experimental electron density and a comparison with high-level theoretical gas-phase calculations show that the crystal environment has a significant influence on the electronic configuration of the sulfonate moiety in 1, which in the crystal is more delocalized than in the gas phase. This crystal effect is mainly due to hydrogen bonding. 相似文献
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Perić B Cordier S Cuny J Gautier R Guizouarn T Planinić P 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(22):6263-6271
Magnetic interactions in solid‐state tantalum cluster compounds have been evidenced by using magnetic susceptibility measurements and corroborated by broken‐symmetry DFT calculations. The three selected compounds are based on [Ta6X12(H2O)6]3+ (X=Cl or/and Br) units with edge‐bridged Ta6 octahedral clusters. Although two of them crystallise in the tetragonal space group I41/a, all compounds exhibit a similar arrangement of paramagnetic clusters related to the diamond structural framework (Fd$\bar 3Magnetic interactions in solid-state tantalum cluster compounds have been evidenced by using magnetic susceptibility measurements and corroborated by broken-symmetry DFT calculations. The three selected compounds are based on [Ta(6)X(12)(H(2)O)(6)](3+) (X=Cl or/and Br) units with edge-bridged Ta(6) octahedral clusters. Although two of them crystallise in the tetragonal space group I4(1)/a, all compounds exhibit a similar arrangement of paramagnetic clusters related to the diamond structural framework (Fd ?3m space group). Magnetic parameters were fitted by using the [5,4] Padé approximant of high-temperature series expansion of susceptibility for the Heisenberg model (S=1/2) in the diamond framework, assuming only nearest-neighbouring interactions. Such a model appropriately describes magnetic-susceptibility measurements at temperatures T>0.7|J|/k. The magnetic interaction parameter J between two [Ta(6)Cl(12)(H(2)O)(6)](3+) clusters is estimated to be -64.28(7) cm(-1) ; it has been enhanced by replacing several chlorine inner ligands with bromine ones (J=-123(3) cm(-1) for two [Ta(6)Br(7.7(1))Cl(4.3(1))(H(2)O)(6)](3+) clusters) and is strongest between two bromine [Ta(6)Br(12)(H(2)O)(6)](3+) clusters with a value of -155(1) cm(-1) . Broken-symmetry DFT calculations within spin-dimer analysis confirmed this trend. Those interactions can be explained on the basis of the overlap between singly occupied a(2u) orbitals localised on neighbouring clusters. 相似文献
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Roth C Peppel T Fumino K Köckerling M Ludwig R 《Angewandte Chemie (International ed. in English)》2010,49(52):10221-10224