共查询到20条相似文献,搜索用时 15 毫秒
1.
Dr. Hajime Kameo Yudai Tanaka Dr. Yoshihiro Shimoyama Daisuke Izumi Prof. Hiroyuki Matsuzaka Dr. Yumiko Nakajima Pierre Lavedan Arnaud Le Gac Dr. Didier Bourissou 《Angewandte Chemie (International ed. in English)》2023,62(20):e202382062
A T-shaped Pt0 complex with a diphosphine-borane (DPB) ligand was prepared. The Pt→B interaction enhances the electrophilicity of the metal and triggers the addition of Lewis bases to give the corresponding tetracoordinate complexes. For the first time, anionic Pt0 complexes are isolated and structurally authenticated. X-ray diffraction analyses show the anionic complexes [(DPB)PtX]− (X=CN, Cl, Br, I) to be square-planar. The d10 configuration and Pt0 oxidation state of the metal were unambiguously established by X-ray photoelectron spectroscopy and DFT calculations. The coordination of Lewis acids as Z-type ligands is a powerful mean to stabilize elusive electron-rich metal complexes and achieve uncommon geometry. 相似文献
2.
Iris Berg Dr. Luca Schio Justus Reitz Dr. Elena Molteni Linoy Lahav Carolina Gutiérrez Bolaños Dr. Andrea Goldoni Dr. Cesare Grazioli Prof. Guido Fratesi Prof. Max M. Hansmann Dr. Luca Floreano Prof. Elad Gross 《Angewandte Chemie (International ed. in English)》2023,62(46):e202311832
Self-assembled monolayers (SAMs) of N-heterocyclic olefins (NHOs) have been prepared on Au(111) and their thermal stability, adsorption geometry, and molecular order were characterized by X-ray photoelectron spectroscopy, polarized X-ray absorption spectroscopy, scanning tunneling microscopy (STM), and density functional theory (DFT) calculations. The strong σ-bond character of NHO anchoring to Au induced high geometrical flexibility that enabled a flat-lying adsorption geometry via coordination to a gold adatom. The flat-lying adsorption geometry was utilized to further increase the surface interaction of the NHO monolayer by backbone functionalization with methyl groups that induced high thermal stability and a large impact on work-function values, which outperformed that of N-heterocyclic carbenes. STM measurements, supported by DFT modeling, identified that the NHOs were self-assembled in dimers, trimers, and tetramers constructed of two, three, and four complexes of NHO−Au-adatom. This self-assembly pattern was correlated to strong NHO−Au interactions and steric hindrance between adsorbates, demonstrating the crucial influence of the carbon-metal σ-bond on monolayer properties. 相似文献
3.
The practical importance of alloy surfaces in catalysis, corrosion andother aspects of materials performance is widely recognized. What is needed now is sufficient knowledge of the relationship between externally controllable factors — alloy composition, temperature, environment — and surface properties — composition, structure, chemical activity — to control materials performance in these applications. Our purpose here is to review progress in determining and predicting the relationship between one surface property, composition, and certain externally controllable variables: overall composition, temperature, environment and physical form.We find that theoretical treatments of metal alloy surface composition now include essentially all significant physical effects and can predict values for most parameters of interest. Though improvements are still possible, the accuracy of predictions is more often limited by uncertainties or absence of the basic data for the calculations (e.g., thermochemical values) than by the models themselves.Alloy surface composition can now be measured well. The first monolayercomposition of large alloy slabs can be determined quantitatively over a wide temperature range in ultra-high vacuum. Difficulties with specimens of practical interest still challenge experimentalists. Among these are supported catalysts, surfaces under chemisorbed layers and composition of layers below the first. Significant progress is being made and we expect the next few years will see success. 相似文献
4.
First the analytical tools, preparation methods and surface crystallography of clean GaAs surfaces are briefly reviewed. Besides the usual methods of cleaving, ion bombardment and annealing, molecular beam epitaxy is mainly used as a growth method under UHV conditions, and has brought a manifold of differently reconstructed structures on the same crystallographic surface, depending on the exact experimental conditions during growth. Quantitative analysis of the surface composition by AES gives the result that these structures differ only in the amount of As in the topmost layer. From the combination of theoretical LEED analysis, UPS results and arguments considering the different physicochemical nature of Ga and As atoms, rehybridisation of the surface atomic bonds emerges as the driving force for reconstruction: the surface Ga atoms try to assume a trivalent planarsp2 and the As atoms a trivalentp3 configuration with three mutually perpendicularp-bonds. The better this rehybridised configuration can be achieved, the better is the chemical stability of the respective structure. The sticking coefficient for oxygen, although generally low, thus varies between ~10-4 and <10-9, depending on the crystallographic surface and, on the same surface, on the degree of surface bond saturation given by the respective structure. However, it emerges that, at least on As-depleted polar surfaces, adsorption proceeds via a mechanism of removal of Ga atoms during exposure and adsorption on the defect sites created in this way. The existence of such a complicated mechanism is consistent with the difficulties arising with the preparation of thick stoichiometric oxide layers, the preparation methods and properties of which are reviewed briefly in the last section. 相似文献
5.
In situ infrared spectroscopy at electrochemical interfaces 总被引:1,自引:0,他引:1
An insight into the in situ FTIR spectroscopy method as applied in Electrochemistry is given. The particular aspects inherent to the electrochemical method are described in a concise form. Selected examples cover the results of about the last 8 years, on a variety of systems including carbon monoxide, small organic molecules and double-layer components (hydrogen, anions and water). The experimental data refer mostly to adsorption on well-defined single-crystal surfaces. Analogies and differences with data from the metal/gas interface are discussed. 相似文献
6.
Shuo Li Yunxia Liu Kun Feng Chengyu Li Jiabin Xu Cheng Lu Prof. Haiping Lin Yong Feng Prof. Ding Ma Prof. Jun Zhong 《Angewandte Chemie (International ed. in English)》2023,62(39):e202308670
Electrochemical water splitting is a promising approach for producing sustainable and clean hydrogen. Typically, high valence state sites are favorable for oxidation evolution reaction (OER), while low valence states can facilitate hydrogen evolution reaction (HER). However, here we proposed a high valence state of Co3+ in Ni9.5Co0.5−S−FeOx hybrid as the favorable center for efficient and stable HER, while structural analogues with low chemical states showed much worse performance. As a result, the Ni9.5Co0.5−S−FeOx catalyst could drive alkaline HER with an ultra-low overpotential of 22 mV for 10 mA cm−2, and 175 mV for 1000 mA cm−2 at the industrial temperature of 60 °C, with an excellent stability over 300 h. Moreover, this material could work for both OER and HER, with a low cell voltage being 1.730 V to achieve 1000 mA cm−2 for overall water splitting at 60 °C. X-ray absorption spectroscopy (XAS) clearly identified the high valence Co3+ sites, while in situ XAS during HER and theoretical calculations revealed the favorable electron capture at Co3+ and suitable H adsorption/desorption energy around Co3+, which could accelerate the HER. The understanding of high valence states to drive reductive reactions may pave the way for the rational design of energy-related catalysts. 相似文献
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8.
Jinwen Hu Wenzhe Shang Cuncun Xin Jingya Guo Xusheng Cheng Songlin Zhang Suchan Song Dr. Wei Liu Dr. Feng Ju Prof. Jungang Hou Prof. Yantao Shi 《Angewandte Chemie (International ed. in English)》2023,62(27):e202304754
Understanding the nature of single-atom catalytic sites and identifying their spectroscopic fingerprints are essential prerequisites for the rational design of target catalysts. Here, we apply correlated in situ X-ray absorption and infrared spectroscopy to probe the edge-site-specific chemistry of Co−N−C electrocatalyst during the oxygen reduction reaction (ORR) operation. The unique edge-hosted architecture affords single-atom Co site remarkable structural flexibility with adapted dynamic oxo adsorption and valence state shuttling between Co(2−δ)+ and Co2+, in contrast to the rigid in-plane embedded Co1−Nx counterpart. Theoretical calculations demonstrate that the synergistic interplay of in situ reconstructed Co1−N2-oxo with peripheral oxygen groups gives a rise to the near-optimal adsorption of *OOH intermediate and substantially increases the activation barrier for its dissociation, accounting for a robust acidic ORR activity and 2e− selectivity for H2O2 production. 相似文献
9.
Meng Yang Dr. Jiafeng Yu Dr. Anna Zimina Dr. Bidyut Bikash Sarma Dr. Lakshmi Pandit Prof. Dr. Jan-Dierk Grunwaldt Ling Zhang Prof. Hengyong Xu Prof. Dr. Jian Sun 《Angewandte Chemie (International ed. in English)》2023,62(7):e202216803
Active Zn species in Cu-based methanol synthesis catalysts have not been clearly identified yet due to their complex nature and dynamic structural changes during reactions. Herein, atomically dispersed Zn on ZrO2 support is established in Cu-based catalysts by separating Zn and Zr components from Cu (Cu−ZnZr) via the double-nozzle flame spray pyrolysis (DFSP) method. It exhibits superiority in methanol selectivity and yield compared to those with Cu−ZnO interface and isolated ZnO nanoparticles. Operando X-ray absorption spectroscopy (XAS) reveals that the atomically dispersed Zn species are induced during the reaction due to the strengthened Zn−Zr interaction. They can suppress formate decomposition to CO and decrease the H2 dissociation energy, shifting the reaction to methanol production. This work enlightens the rational design of unique Zn species by regulating coordination environments and offers a new perspective for exploring complex interactions in multi-component catalysts. 相似文献
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11.
Bersillon JL Villieras F Bardot F Gorner T Cases JM 《Journal of colloid and interface science》2001,240(2):400-411
In environmental engineering, adsorption and desorption are phenomena commonly referred to as responsible for pollution dispersion, retention, or retardation in soils, aquifers, and hydrologic systems. They are also used to remove organic pollutants from water or odorous compounds in gas deodorization. Most often, the characterization of the aqueous adsorption systems that are of engineering interest involves a narrow adsorbate concentration range and low values of the adsorbate concentration. The practice is to use the Freundlich equation that best fits most data and is considered sufficient to design adsorption contactors. However, no physical or chemical meaning can be associated with the values taken by the parameters. The present paper gives a new way of analyzing adsorption data, using an extension of the Freundlich equation and the Gaussian distribution function that makes it possible to associate parameter values of this extension with the adsorbate–adsorbent normal interaction energy, its heterogeneity, and to some extent the adsorbate–adsorbate lateral interaction energy. 相似文献
12.
Zhiguo Sun Huijuan Zhang Linlin Cao Xiaokang Liu Dan Wu Xinyi Shen Xue Zhang Zihang Chen Sen Ru Xiangyu Zhu Zhiyuan Xia Qiquan Luo Faqiang Xu Prof. Tao Yao 《Angewandte Chemie (International ed. in English)》2023,62(13):e202217719
The construction and understanding of synergy in well-defined dual-atom active sites is an available avenue to promote multistep tandem catalytic reactions. Herein, we construct a dual-hetero-atom catalyst that comprises adjacent Cu-N4 and Se-C3 active sites for efficient oxygen reduction reaction (ORR) activity. Operando X-ray absorption spectroscopy coupled with theoretical calculations provide in-depth insights into this dual-atom synergy mechanism for ORR under realistic device operation conditions. The heteroatom Se modulator can efficiently polarize the charge distribution around symmetrical Cu-N4 moieties, and serve as synergistic site to facilitate the second oxygen reduction step simultaneously, in which the key OOH*-(Cu1-N4) transforms to O*-(Se1-C2) intermediate on the dual-atom sites. Therefore, this designed catalyst achieves satisfied alkaline ORR activity with a half-wave potential of 0.905 V vs. RHE and a maximum power density of 206.5 mW cm−2 in Zn-air battery. 相似文献
13.
Yi-Hsuan Wu Harshit Mehta Dr. Elena Willinger Dr. Jodie A. Yuwono Dr. Priyank V. Kumar Dr. Paula M. Abdala Dr. Anna Wach Dr. Agnieszka Kierzkowska Dr. Felix Donat Dr. Denis A. Kuznetsov Prof. Dr. Christoph R. Müller 《Angewandte Chemie (International ed. in English)》2023,62(8):e202217186
Establishing generic catalyst design principles by identifying structural features of materials that influence their performance will advance the rational engineering of new catalytic materials. In this study, by investigating metal-substituted manganese oxide (spinel) nanoparticles, Mn3O4:M (M=Sr, Ca, Mg, Zn, Cu), we rationalize the dependence of the activity of Mn3O4:M for the electrocatalytic oxygen reduction reaction (ORR) on the enthalpy of formation of the binary MO oxide, ΔfH°(MO), and the Lewis acidity of the M2+ substituent. Incorporation of elements M with low ΔfH°(MO) enhances the oxygen binding strength in Mn3O4:M, which affects its activity in ORR due to the established correlation between ORR activity and the binding energy of *O/*OH/*OOH species. Our work provides a perspective on the design of new compositions for oxygen electrocatalysis relying on the rational substitution/doping by redox-inactive elements. 相似文献
14.
We have investigated the adsorption of nine different adatoms on the (111) and (100) surfaces of Iridium (Ir) using first principles density functional theory. The study explores surface functionalization of Ir which would provide important information for further study of its functionality in catalysis and other surface applications. The adsorption energy, stable geometry, density of states and magnetic moment are some of the physical quantities of our interest. The study reveals that the three-/four- fold hollow site is energetically the most favorable adsorption site on the (111)/(100) surface of Ir. The investigation on a wide range of coverages (from 0.04 to 1 monolayer) reveals the strong coverage dependence of adsorption energy of the adsorbate atoms. The adsorption energy is found to increase as the coverage increases, implying a repulsive interaction between the adsorbates. Strong hybridization between the adsorbates and the substrate electronic states is revealed to impact the adsorption, while the magnetic moment of the adsorbates is found to be suppressed. The Bader analysis reveals significant amount of charge transfers between the adsorbate atoms and the substrate. The binding of adsorbate atoms on the (100) surface is observed to be moderately stronger as compared to that on the (111) surface. 相似文献
15.
The theory of a surface electrochemical reaction (strong adsorption) occurring in two le− steps O?R? X, when R can undergo a dimerization R → D and X a first-order reaction X → Z is presented for polarography. It is assumed that adsorption obeys a Langmuir isotherm. The equation of the half-wave potentials as functions of the diverse parameters (rate constants, concentration, surface concentration, drop time) are given; the effects of the two chemical reactions are additive. Kinetic diagrams are constructed. The results can be used to diagnose the type of reaction and to calculate the chemical rate constants.The effects of the dimerization on the half-wave potentials of the two stages do not depend on their separation; in the case of a global 2e− step, they remain hidden until the rate becomes large enough to cause a splitting into two le− waves. These results are generalized to the case where the electrochemical reactions are heterogeneous, and the chemical reactions homogeneous. 相似文献
16.
Nitrogen Adsorption Studies of PAN-Based Activated Carbon Fibers Prepared by Different Activation Methods 总被引:1,自引:0,他引:1
Polyacrylonitrile (PAN)-based activated carbon fibers (ACFs) prepared by various activation methods were characterized using low-temperature nitrogen adsorption over a wide relative pressure from 10−6 to 1. Nitrogen adsorption is a standard tool for determination of porous structure parameters. In the present work, we carried out extensive adsorption studies of a series of PAN-ACFs activated by different methods. It was shown that the high-resolution αS plot provided valuable information about structural properties of samples under study. The pore size distributions of samples under study were calculated by employing the regularization method according to density functional theory. By these analyses, the pore development and the dominant pores of samples prepared by different methods can be clearly observed. Moreover, the adsorption measurement could provide profound insight into the structural heterogeneity of the ACFs. 相似文献
17.
Sicong Wang Tao Ding Tong Liu Yanan Zhu Zhinan Tao Beibei Pang Xiaokang Liu Qiquan Luo Mei Sun Hongting Sheng Prof. Manzhou Zhu Prof. Tao Yao 《Angewandte Chemie (International ed. in English)》2023,62(16):e202303150
The transformation from metal nanocluster catalysts to metal single-atom catalysts is an important procedure in the rational design of atomically dispersed metal catalysts (ADCs). However, the conversion methods often involve high annealing temperature as well as reducing atmosphere. Herein, we reported a continuous and convenient approach to transfer Pd nanocluster into Pd single-atom in a ligand assisted annealing procedure, by which means we reduced its activating temperature low to 400 °C. Using ex-situ microscopy and spectroscopy, we comprehensively monitored the structural evolution of Pd species though the whole atomization process. Theoretical calculation revealed that the structural instability caused by remaining Cl ligands was the main reason for this low-temperature transformation. The present atomization strategy and mechanistic knowledge for the conversion from cluster to atomic dispersion provides guidelines for the rational design of ADCs. 相似文献
18.
用延展X射线吸收精细结构(EXAFS)光谱和密度泛函理论(DFT)研究了As(V)-TiO2体系的吸附机理. 离子强度变化对As(V)-TiO2体系吸附无显著影响, 表明吸附后形成了内层络合物. EXAFS结果表明, As(V)原子主要通过—AsO4上的O原子结合到TiO2表面上, 平均As-O原子间距(R)在吸附前后无明显变化, 保持在(0.169±0.001) nm. As-Ti层的EXAFS分析结果与DFT计算的吸附构型的As-Ti原子间距对照表明, 体系存在两种主要亚稳平衡吸附(MEA)结构, 即对应于R1=(0.321±0.002) nm 的双角(DC)强吸附构型和R2=(0.360±0.002) nm的单角(SC)弱吸附构型. 而且随着吸附量由9.79 mg·g-1增加至28.0 mg·g-1, 吸附样品中双角构型配位数与单角构型配位数的比值(CN1/CN2)从3.3降低到1.6, 说明双角亚稳平衡吸附结构在低覆盖度时占优势, 而在高表面覆盖度时单角亚稳平衡吸附结构占优势, 即在表面覆盖度较大时, As(V)在TiO2表面上倾向于形成单角构型. 相似文献
19.
Mantovani D. Castonguay M. Pageau J. F. Fiset M. Laroche G. 《Plasmas and Polymers》1999,4(2-3):207-228
A cylindrically-configured plasma treatment system in Radio Frequency Glow Discharges fed with ammonia was used to modify the internal surface of ePTFE arterial prostheses. The effects of RF power, NH3 pressure, and treatment time on the surface chemical composition were characterized by XPS. The effect of moving the prosthesis within the plasma on the homogeneity of the surface treatment was also investigated. XPS studies were conducted in order to investigate the evolution of the treated surface during storage in atmosphere or water. Results show that the treatment at 20 W, for 250 seconds and under an ammonia pressure of 300 mTorr yielded a good compromise between ablation and substitution phenomena on the surface. With this treatment, fluorine content was decreased, while up to 11.6% of the surface atoms were substituted by nitrogen. Atmospheric storage up to 80 days shows a remodeling and oxidation of the surface by introducing up to 14.5% of oxygen. Finally, immersion in water for up to 7 hours showed a rapid defluorination of the treated surface. 相似文献
20.
The adsorption and decomposition of water on Ge(100) have been investigated using real-time scanning tunneling microscopy (STM) and density-functional theory (DFT) calculations. The STM results revealed two distinct adsorption features of H2O on Ge(100) corresponding to molecular adsorption and H-OH dissociative adsorption. In the molecular adsorption geometry, H2O molecules are bound to the surface via Ge-O dative bonds between the O atom of H2O and the electrophilic down atom of the Ge dimer. In the dissociative adsorption geometry, the H2O molecule dissociates into H and OH, which bind covalently to a Ge-Ge dimer on Ge(100) in an H-Ge-Ge-OH configuration. The DFT calculations showed that the dissociative adsorption geometry is more stable than the molecular adsorption geometry. This finding is consistent with the STM results, which showed that the dissociative product becomes dominant as the H2O coverage is increased. The simulated STM images agreed very well with the experimental images. In the real-time STM experiments, we also observed a structural transformation of the H2O molecule from the molecular adsorption to the dissociative adsorption geometry. 相似文献