共查询到20条相似文献,搜索用时 31 毫秒
1.
Dr. Alessandro Longo Dr. Ewoud J. J. de Boed Dr. Nisha Mammen Dr. Marte van der Linden Prof. Dr. Karoliina Honkala Prof. Dr. Hannu Häkkinen Prof. Dr. Petra E. de Jongh Dr. Baira Donoeva 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(31):7051-7058
Controlling the size and uniformity of metal clusters with atomic precision is essential for fine-tuning their catalytic properties, however for clusters deposited on supports, such control is challenging. Here, by combining X-ray absorption spectroscopy and density functional theory calculations, it is shown that supports play a crucial role in the evolution of monolayer-protected clusters into catalysts. Based on the acidic nature of the support, cluster-support interactions lead either to fragmentation of the cluster into isolated Au–ligand species or ligand-free metallic Au0 clusters. On Lewis acidic supports that bind metals strongly, the latter transformation occurs while preserving the original size of the metal cluster, as demonstrated for various Aun sizes. These findings underline the role of the support in the design of supported catalysts and represent an important step toward the synthesis of atomically precise supported nanomaterials with tailored physico-chemical properties. 相似文献
2.
Martin Baron Heather Abbott Dr. Oleksandr Bondarchuk Dr. Dario Stacchiola Dr. Alexander Uhl Dr. Shamil Shaikhutdinov Dr. Hans‐Joachim Freund Prof. Dr. Cristina Popa Dr. Maria Veronica Ganduglia‐Pirovano Dr. Joachim Sauer Prof. Dr. 《Angewandte Chemie (International ed. in English)》2009,48(43):8006-8009
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Dr. Stewart F. Parker Dr. Sanghamitra Mukhopadhyay Dr. Mónica Jiménez-Ruiz Dr. Peter W. Albers 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(26):6496-6499
The interaction of hydrogen with platinum is enormously important in many areas of catalysis. The most significant of these are in polymer electrolyte membrane fuel cells (PEMFC), in which carbon-supported platinum is used to dissociate hydrogen gas at the anode. The nature of adsorbed hydrogen on platinum has been studied for many years on single-crystal surfaces, on high-surface area-platinum metal (Raney platinum and platinum black), and on supported catalysts. Many forms of vibrational spectroscopy have played a key role in these studies, however, there is still no clear consensus as to the assignment of the spectra. In this work, ab initio molecular dynamics (AIMD) and lattice dynamics were used to study a 1.1 nm nanoparticle, Pt44H80. The results were compared to new inelastic neutron scattering spectra of hydrogen on platinum black and of a carbon-supported platinum fuel cell catalyst and an assignment scheme that rationalises all previous data is proposed. 相似文献
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Timothy J. Schmeier Dr. Ainara Nova Prof. Dr. Nilay Hazari Prof. Dr. Feliu Maseras 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(22):6915-6927
The Ni amide and hydroxide complexes [(PCP)Ni(NH2)] ( 2 ; PCP=bis‐2,6‐di‐tert‐butylphosphinomethylbenzene) and [(PCP)Ni(OH)] ( 3 ) were prepared by treatment of [(PCP)NiCl] ( 1 ) with NaNH2 or NaOH, respectively. The conditions for the formation of 3 from 1 and NaOH were harsh (2 weeks in THF at reflux) and a more facile synthetic route involved protonation of 2 with H2O, to generate 3 and ammonia. Similarly the basic amide in 2 was protonated with a variety of other weak acids to form the complexes [(PCP)Ni(2‐Me‐imidazole)] ( 4 ), [(PCP)Ni(dimethylmalonate)] ( 5 ), [(PCP)Ni(oxazole)] ( 6 ), and [(PCP)Ni(CCPh)] ( 7 ), respectively. The hydroxide compound 3 , could also be used as a Ni precursor and treatment of 3 with TMSCN (TMS=trimethylsilyl) or TMSN3 generated [(PCP)Ni(CN)] ( 8 ) or [(PCP)Ni(N3)] ( 9 ), respectively. Compounds 3–7 , and 9 were characterized by X‐ray crystallography. Although 3 , 4 , 6 , 7 , and 9 are all four‐coordinate complexes with a square‐planar geometry around Ni, 5 is a pseudo‐five‐coordinate complex, with the dimethylmalonate ligand coordinated in an X‐type fashion through one oxygen atom, and weakly as an L‐type ligand through another oxygen atom. Complexes 2–9 were all reacted with carbon dioxide. Compounds 2 – 4 underwent facile reaction at low temperature to form the κ1‐O carboxylate products [(PCP)Ni{OC(O)NH2}] ( 10 ), [(PCP)Ni{OC(O)OH}] ( 11 ), and [(PCP)Ni{OC(O)‐2‐Me‐imidazole}] ( 12 ), respectively. Compounds 10 and 11 were characterized by X‐ray crystallography. No reaction was observed between 5 – 9 and carbon dioxide, even at elevated temperatures. DFT calculations were performed to model the thermodynamics for the insertion of carbon dioxide into 2 – 9 to form a κ1‐O carboxylate product and understand the pathways for carbon dioxide insertion into 2 , 3 , 6 , and 7 . The computed free energies indicate that carbon dioxide insertion into 2 and 3 is thermodynamically favorable, insertion into 8 and 9 is significantly uphill, insertion into 5 and 7 is slightly uphill, and insertion into 4 and 6 is close to thermoneutral. The pathway for insertion into 2 and 3 has a low barrier and involves nucleophilic attack of the nitrogen or oxygen lone pair on electrophilic carbon dioxide. A related stepwise pathway is calculated for 7 , but in this case the carbon of the alkyne is significantly less nucleophilic and as a result, the barrier for carbon dioxide insertion is high. In contrast, carbon dioxide insertion into 6 involves a single concerted step that has a high barrier. 相似文献
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Francesco Napoli Dr. Mario Chiesa Dr. Elio Giamello Prof. Gloria Preda Dr. Cristiana Di Valentin Dr. Gianfranco Pacchioni Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(23):6776-6785
The formation of O2? radical anions by contact of O2 molecules with a Na pre‐covered MgO surface is studied by a combined EPR and quantum chemical approach. Na atoms deposited on polycrystalline MgO samples are brought into contact with O2. The typical EPR signal of isolated Na atoms disappears when the reaction with O2 takes place and new paramagnetic species are observed, which are attributed to different surface‐stabilised O2? radicals. Hyperfine sublevel correlation (HYSCORE) spectroscopy allows the superhyperfine interaction tensor of O2?Na+ species to be determined, demonstrating the direct coordination of the O2? adsorbate to surface Na+ cations. DFT calculations enable the structural details of the formed species to be determined. Matrix‐isolated alkali superoxides are used as a standard to enable comparison of the formed species, revealing important and unexpected contributions of the MgO matrix in determining the electronic structure of the surface‐stabilised Na+? O2? complexes. 相似文献
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Céline Chizallet Dr. Pascal Raybaud Dr. 《Angewandte Chemie (International ed. in English)》2009,48(16):2891-2893
Amorphization tunes acidity : Pseudo‐bridging silanols, suggested as versatile Brønsted acid groups by molecular modeling studies, are obtained by shifted hydrolysis of Si? O? Al bridges formed by the thermal treatment of silica deposited on γ‐Al2O3 (100), and appear under given pretreatment conditions. Demixing of part of the silica from the aluminosilicate phase is predicted upon excess water adsorption.
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Artur Mardyukov Rachel Crespo‐Otero Dr. Elsa Sanchez‐Garcia Dr. Wolfram Sander Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(29):8679-8689
The reaction of the phenyl radical 1 with water has been investigated by using matrix isolation spectroscopy and quantum chemical calculations. The primary thermal product of the reaction between 1 and water is a weakly bound complex stabilized by an OH???π interaction. This complex is photolabile, and visible‐light irradiation (λ>420 nm) results in hydrogen atom transfer from water to radical 1 and the formation of a highly labile complex between benzene and the OH radical. This complex is stable under the conditions of matrix isolation, however, continuous irradiation with λ>420 nm light results in the complete destruction of the aromatic system and formation of an acylic unsaturated ketene. The mechanisms of all reaction steps are discussed in the light of ab initio and DFT calculations. 相似文献
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Chemical Reactivity and Band‐Gap Opening of Graphene Doped with Gallium,Germanium, Arsenic,and Selenium Atoms 下载免费PDF全文
Dr. Pablo A. Denis 《Chemphyschem》2014,15(18):3994-4000
Herein, the effects of substitutional doping of graphene with Ga, Ge, As, and Se are shown. Ge exhibits the lowest formation energy, whereas Ga has the largest one. Ga‐ and As‐doped graphene display a reactivity that is larger than that corresponding to a double vacancy. They can decompose H2 and O2 easily. Variation of the type and concentration of dopant makes the adjustment of the interlayer interaction possible. In general, doping of monolayer graphene opens a band gap. At some concentrations, Ga doping induces a half metallic behavior. As is the element that offers the widest range of gap tuning. Heyd–Scuseria–Ernzerhof calculations indicate that it can be varied from 1.3 to 0.3 eV. For bilayer graphene, the doped sheet induces charge redistribution in the perfect underneath sheet, which opens a gap in the range of 0.05–0.4 eV. This value is useful for developing graphene‐based electronics, as the carrier mobility of the undoped sheet is not expected to alter. 相似文献
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Theano Petsi Dr. George D. Panagiotou Dr. Christos S. Garoufalis Dr. Christos Kordulis Prof. Panagiota Stathi Dr. Yiannis Deligiannakis Prof. Alexis Lycourghiotis Prof. Kyriakos Bourikas Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(47):13090-13104
The interfacial chemistry of the impregnation step involved in the synthesis of cobalt catalysts supported on titania was investigated with regard to the mode of interfacial deposition of the aqua complex [Co(H2O)6]2+ on the “titania/electrolyte solution” interface, the structure of the inner‐sphere complexes formed, and their relative interfacial concentrations. Several methodologies based on the application of deposition experiments and electrochemical techniques were used in conjunction with diffuse‐reflectance spectroscopy and EPR spectroscopy. These suggested the formation of mononuclear/oligonuclear inner‐sphere complexes on deposition of the [Co(H2O)6]2+ ions at the “titania/electrolyte solution” interface. The joint application of semiempirical quantum‐mechanical calculations, stereochemical considerations, and modeling of the deposition data revealed the exact structure of these complexes and allowed their relative concentrations at various CoII surface concentrations to be determined. It was found that the interface speciation depends on the CoII surface concentration. Mononuclear complexes are formed at the compact layer of the “titania/electrolyte solution” interface for low and medium CoII surface concentrations. Formation of mono‐hydrolyzed Ti2O–TiO and the dihydrolyzed TiO–TiO disubstituted configurations is very probable. In the first configuration one water ligand of the [Co(H2O)6]2+ ion is substituted by a bridging surface oxygen atom and another by a terminal surface oxygen atom. In the second configuration two water ligands of the [Co(H2O)6]2+ ion are substituted by two terminal surface oxygen atoms. Binuclear and trinuclear inner‐sphere complexes are formed, in addition to the mononuclear ones, at relatively high CoII surface concentrations. 相似文献
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Structure of Framework Aluminum Lewis Sites and Perturbed Aluminum Atoms in Zeolites as Determined by 27Al{1H} REDOR (3Q) MAS NMR Spectroscopy and DFT/Molecular Mechanics 下载免费PDF全文
Dr. Jiří Brus Libor Kobera Dr. Wolfgang Schoefberger Dr. Martina Urbanová Petr Klein Dr. Petr Sazama Dr. Edyta Tabor Dr. Stepan Sklenak Dr. Anna V. Fishchuk Dr. Jiří Dědeček 《Angewandte Chemie (International ed. in English)》2015,54(2):541-545
Zeolites are highly important heterogeneous catalysts. Besides Brønsted SiOHAl acid sites, also framework AlFR Lewis acid sites are often found in their H‐forms. The formation of AlFR Lewis sites in zeolites is a key issue regarding their selectivity in acid‐catalyzed reactions. The local structures of AlFR Lewis sites in dehydrated zeolites and their precursors—“perturbed” AlFR atoms in hydrated zeolites—were studied by high‐resolution MAS NMR and FTIR spectroscopy and DFT/MM calculations. Perturbed framework Al atoms correspond to (SiO)3AlOH groups and are characterized by a broad 27Al NMR resonance (δi=59–62 ppm, CQ=5 MHz, and η=0.3–0.4) with a shoulder at 40 ppm in the 27Al MAS NMR spectrum. Dehydroxylation of (SiO)3AlOH occurs at mild temperatures and leads to the formation of AlFR Lewis sites tricoordinated to the zeolite framework. Al atoms of these (SiO)3Al Lewis sites exhibit an extremely broad 27Al NMR resonance (δi≈67 ppm, CQ≈20 MHz, and η≈0.1). 相似文献
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Controllable Scission and Seamless Stitching of Metal–Organic Clusters by STM Manipulation 下载免费PDF全文
Huihui Kong Likun Wang Qiang Sun Chi Zhang Dr. Qinggang Tan Prof. Dr. Wei Xu 《Angewandte Chemie (International ed. in English)》2015,54(22):6526-6530
Scanning tunneling microscopy (STM) manipulation techniques have proven to be a powerful method for advanced nanofabrication of artificial molecular architectures on surfaces. With increasing complexity of the studied systems, STM manipulations are then extended to more complicated structural motifs. Previously, the dissociation and construction of various motifs have been achieved, but only in a single direction. In this report, the controllable scission and seamless stitching of metal–organic clusters have been successfully achieved through STM manipulations. The system presented here includes two sorts of hierarchical interactions where coordination bonds hold the metal–organic elementary motifs while hydrogen bonds among elementary motifs are directly involved in bond breakage and re‐formation. The key to making this reversible switching successful is the hydrogen bonding, which is comparatively facile to be broken for controllable scission, and, on the other hand, the directional characteristic of hydrogen bonding makes precise stitching feasible. 相似文献
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Dr. Manyi Duan Jian Yu Jun Meng Dr. Beien Zhu Prof. Yong Wang Prof. Yi Gao 《Angewandte Chemie (International ed. in English)》2018,57(22):6464-6469
Metal nanoparticles (NPs) dispersed on a high‐surface‐area support are normally used as heterogeneous catalysts. Recent in situ experiments have shown that structure reconstruction of the NP occurs in real catalysis. However, the role played by supports in these processes is still unclear. Supports can be very important in real catalysis because of the new active sites at the perimeter interface between nanoparticles and supports. Herein, using a developed multiscale model coupled with in situ spherical aberration‐corrected (Cs‐corrected) TEM experiments, we show that the interaction between the support and the gas environment greatly changes the contact surface area between the metal and support, which further leads to the critical change in the perimeter interface. The dynamic changes of the interface in reactive environments can thus be predicted and be included in the rational design of supported metal nanocatalysts. In particular, our multiscale model shows quantitative consistency with experimental observations. This work offers possibilities for obtaining atomic‐scale structures and insights beyond the experimental limits. 相似文献
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Dynamic Changes in the Structure,Chemical State and Catalytic Selectivity of Cu Nanocubes during CO2 Electroreduction: Size and Support Effects 下载免费PDF全文
Philipp Grosse Dunfeng Gao Fabian Scholten Ilya Sinev Hemma Mistry Beatriz Roldan Cuenya 《Angewandte Chemie (International ed. in English)》2018,57(21):6192-6197
In situ and operando spectroscopic and microscopic methods were used to gain insight into the correlation between the structure, chemical state, and reactivity of size‐ and shape‐controlled ligand‐free Cu nanocubes during CO2 electroreduction (CO2RR). Dynamic changes in the morphology and composition of Cu cubes supported on carbon were monitored under potential control through electrochemical atomic force microscopy, X‐ray absorption fine‐structure spectroscopy and X‐ray photoelectron spectroscopy. Under reaction conditions, the roughening of the nanocube surface, disappearance of the (100) facets, formation of pores, loss of Cu and reduction of CuOx species observed were found to lead to a suppression of the selectivity for multi‐carbon products (i.e. C2H4 and ethanol) versus CH4. A comparison with Cu cubes supported on Cu foils revealed an enhanced morphological stability and persistence of CuI species under CO2RR in the former samples. Both factors are held responsible for the higher C2/C1 product ratio observed for the Cu cubes/Cu as compared to Cu cubes/C. Our findings highlight the importance of the structure of the active nanocatalyst but also its interaction with the underlying substrate in CO2RR selectivity. 相似文献
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A Study of Overheating of Thermostatically Controlled TiO2 Thin Films by Using Raman Spectroscopy 下载免费PDF全文
Dr. Juan Jesús Gallardo Dr. Javier Navas Dr. David Zorrilla Dr. Rodrigo Alcántara Diego Valor Dr. Antonio Sánchez‐Coronilla Dr. Norge Cruz Hernández Dr. Concha Fernández‐Lorenzo Prof. Dr. Joaquín Martín‐Calleja 《Chemphyschem》2015,16(18):3949-3958
In this study a classic Raman spectroscopy method is applied and the intensity ratio of Stokes and anti‐Stokes peaks is used to measure the temperature of thermostatically controlled TiO2 thin films. In addition, three mathematical formulae are used and analyzed to estimate the temperature of the TiO2 thin films. Overheating of the samples above the thermostatically controlled temperature was observed while recording the Raman spectra, with a temperature increase of up to 30 K being detected. DFT‐periodic calculations showed that the anatase (101) surface had a smaller band gap than bulk anatase. Thus, it can absorb the laser radiation with a wavelength of 532 nm that is used in the experimental setup. Part of the absorbed photon energy transfers into phonon energy, heating up the anatase phase, thus leading to the heating of the samples. Moreover, overheating of the samples indicates that the experimental method used in this study can lead to deviations in their real absolute temperature values. 相似文献
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Spectroscopic techniques are valuable tools for understanding the structure and dynamics of complex systems, such as biomolecules or nanomaterials. Most of the current research is devoted to the development of new experimental techniques for improving the intrinsic resolution of different spectra. However, the subtle interplay of several different effects acting at different length and time scales still makes the interpretation and analysis of such spectra a very difficult task. In this respect, computational spectroscopy is becoming a needful and versatile tool for the assignment and interpretation of experimental spectra. It is in fact possible nowadays to model with relatively high accuracy the physical–chemical properties of complex molecules in different environments, and to link spectroscopic evidence directly to the structural and dynamical properties of optically or magnetically active solvated probes. In this Review, significant steps toward the simulation of entire spectra in condensed phases are presented together with some basic aspects of computational spectroscopy, which highlight how intramolecular and intermolecular degrees of freedom influence several spectroscopic parameters. 相似文献