共查询到20条相似文献，搜索用时 0 毫秒
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Wei Liu;Hongpeng Liu;Ronghua Cui;Zhongliang Cao;Zejian Dong;Langli Luo; 《Small (Weinheim an der Bergstrasse, Germany)》2024,20(4):2305122
Metal–support interaction (MSI) provides great possibilities to tune the activity, selectivity, and stability of heterogeneous catalysts. Herein, the Au/ZnO catalyst is prepared by commercial ZnO and chloroauric acid, and the structure evolution of the catalyst pretreated by H2 and O2 gas at varied temperature is investigated to provide mechanistic insights of MSI. It is found that the H2 treatment at 300 °C and above can induce the formation of both the ZnOx overlayer and bulk Au–Zn alloy. In contrast, the O2 treatment can form the ZnOx overlayer at 500 °C and above without the formation of Au–Zn alloy. It is also revealed that the ZnOx overlayer is dynamically stable (permeable), which can provide access for reactant molecules during the reaction process. And, the Au–Zn alloy can recover to Au and ZnO under the CO oxidation reaction condition, which can be deemed as a re-activation process that endows H2-treated samples with the superior activity and stability. 相似文献
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The CO oxidation behaviour of planar Au/TiO2 model catalysts was studied by a combination of kinetic measurements and in-situ IR measurements under realistic pressure and temperature conditions (p = 20 mbar, T = 80 °C). During reaction in a CO/O2 mixture, the model catalysts deactivated significantly. Adding small amounts of H2O (1000 ppm) to the reactive CO/O2 gas mixture, the catalyst activity increased markedly, by at least one order of magnitude. Furthermore, in-situ IR measurements show a decrease of the amount of adsorbed by-products of the CO oxidation, and a change of the predominant by-product from surface carbonate to surface formate. Possible reasons for the deactivation are discussed and the effect of H2O addition is compared to results of similar studies on more realistic dispersed catalysts. 相似文献
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一直以来,金属纳米材料有着非常重要的应用价值且受到广泛关注,金属团簇碰撞合并过程的研究成果对认清团簇的沉积和纳米金属膜及块体材料的形成有重要的意义。采用Johnson的嵌入原子势(Embeded atom method,EAM)模型并结合分子动力学模拟方法,模拟金原子团簇在不同的碰撞平动速度作用下的碰撞合并过程,仅给弹团簇一定大小的碰撞动能,迫使两个团簇产生相对速度并发生相互碰撞合并,研究在不同的碰撞平动速度下和不同的团簇大小下对团簇碰撞合并过程产生的影响及对碰撞合并之后新团簇的性质产生的影响。在进行模拟碰撞之前,先对团簇进行了\"退火\"处理,只模拟了同等尺度大小的两个金原子团簇之间的碰撞合并过程。 相似文献
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Wu Z Wang M Yang J Zheng X Cai W Meng G Qian H Wang H Jin R 《Small (Weinheim an der Bergstrasse, Germany)》2012,8(13):2028-2035
The fluorescence of nanoparticles has attracted much attention in recent research, but in many cases the underlying mechanisms are difficult to evaluate due to the polydispersity of nanoparticles and their unknown structures, in particular the surface structures. Recent breakthroughs in the syntheses and structure determinations of well-defined gold nanoclusters provide opportunities to conduct in-depth investigations. Devising well-defined nanocluster sensors based on fluorescence change is of particular interest not only for scientific studies but also for practical applications. Herein, the potential of the glutathionate (SG)-capped Au(25) nanocluster as a silver ion sensor is evaluated. The Ag(+) detection limit of approximately 200 nM, based on the fluorescence enhancement and good linear fluorescence response in the silver ion concentration range from 20 nM to 11 μM, in combination with the good selectivity among 20 types of metal cations, makes Au(25) (SG)(18) a good candidate for fluorescent sensors for silver ions. Further experiments reveal three important factors responsible for the unique fluorescence enhancement caused by silver ions: 1) the oxidation state change of Au(25) (SG)(18) ; 2) the interaction of neutral silver species (Ag(0) , reduced by Au(25) (SG)(18) (-) ) with Au(25) (SG)(18) ; and 3) the interaction of Ag(+) with Au(25) (SG)(18.) Experiments demonstrate the very different chemistry of hydrophobic Au(25) (SC(2) H(4) Ph)(18) and hydrophilic Au(25) (SG)(18) in the reaction with silver ions. This work indicates another potential application of gold nanoclusters, offers new strategies for nanocluster-based chemical sensing, and reveals a new way to influence nanocluster chemistry for potential applications. 相似文献
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Han Y He DS Liu Y Xie S Tsukuda T Li ZY 《Small (Weinheim an der Bergstrasse, Germany)》2012,8(15):2361-2364
A method of single-shot imaging via aberration-corrected scanning transmission electron microscopy equipped with high angle annular dark-field detector (STEM-HAADF) has been applied to size-selected gold model catalysts (Au(25) and Au(39) ) on hydroxyapatite. Through quantitative intensity analysis, the size, in terms of number of atoms as well as 3D shape of the clusters are obtained. 相似文献
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Xiuxin Wang Jiandong Yang Huajie Yin Rui Song Zhiyong Tang 《Advanced materials (Deerfield Beach, Fla.)》2013,25(19):2728-2732
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Synthesis of Pd nanocrystals enclosed by {100} facets and with sizes <10 nm for application in CO oxidation 总被引：1，自引：0，他引：1
Mingshang Jin Hongyang Liu Hui Zhang Zhaoxiong Xie Jingyue Liu Younan Xia 《Nano Research》2011,4(1):83-91
The catalytic activity of noble-metal nanocrystals is mainly determined by their sizes and the facets exposed on the surface.
For single crystals, it has been demonstrated that the Pd(100) surface is catalytically more active than both Pd(110) and
Pd(111) surfaces for the CO oxidation reaction. Here we report the synthesis of Pd nanocrystals enclosed by {100} facets with
controllable sizes in the range of 6–18 nm by manipulating the rate of reduction of the precursor. UV-vis spectroscopy studies
indicate that the rate of reduction of Na2PdCl4 can be controlled by adjusting the concentrations of Br− and Cl− ions added to the reaction mixture. Pd nanocrystals with different sizes were immobilized on ZnO nanowires and evaluated
as catalysts for CO oxidation. We found that the activity of this catalytic system for CO oxidation showed a strong dependence
on the nanocrystal size. When the size of the Pd nanocrystals was reduced from 18 nm to 6 nm, the maximum conversion rate
was significantly enhanced by a factor of ∼10 and the corresponding maximum conversion temperature was lowered by ∼80 °C. 相似文献
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Florian Weigend Ferdinand Evers Jrg Weissmüller 《Small (Weinheim an der Bergstrasse, Germany)》2006,2(12):1391-1391
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Space-charge layers can noticeably affect the properties of metal electrode surfaces, for instance by modifying the surface dielectric response or indirectly via the induced atomic relaxations. While there are efforts to exploit this concept for designing novel functional nanomaterials, the underlying microscopic processes are poorly understood. Here, we report on a density functional theory (DFT) study of atomic relaxation in Au cluster ions comprising up to 309 atoms. Suitable averages over atomic displacements respond to charging consistent with experimental observation on macroscopic Au single-crystal surfaces. Moreover, the overall DFT response is also consistent with predictions of a simple phenomenological model. Motivated by our observations, we propose a scenario in which the surface relaxation (\"stretch\") results from out-of-plane Hellman-Feynman forces exerted on the surface atoms by the excess charge, and where the in-plane surface stress represents essentially an elastic transverse contraction tendency of the surface layer in response to stretch. 相似文献
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The proof of concept of a simple sensing platform based on the fluorescence of a gold cluster consisting of eight atoms, which is easily manipulated by reduction and oxidation of a specific molecule in the absence of chemical linkers, is demonstrated. Without using any coupling reagents to arrange the distance of the donor-acceptor pair, the fluorescence of the Au(8) -cluster is immediately switched off in the presence of 2-pyridinethiol (2-PyT) quencher. Through an upward-curving Stern-Volmer plot, the system shows complex fluorescence quenching with a combination of static and dynamic quenching processes. To analyze the static quenching constant (V) by a \"sphere of action\" model, the collisional encounter between the Au(8) -cluster and 2-PyT presents a quenching radius (r) ≈5.8 nm, which is larger than the sum of the radii of the Au(8) -cluster and 2-PyT. This implies that fluorescence quenching can occur even though the Au(8) -cluster and 2-PyT are not very close to each other. The quenching pathway may be derived from a photoinduced electron-transfer process of the encounter pair between the Au(8) -cluster (as an electron donor) and 2-PyT (as an electron acceptor) to allow efficient fluorescence quenching in the absence of coupling reagents. Interestingly, the fluorescence is restored by oxidation of 2-PyT to form the corresponding disulfide compound and then quenched again after the reduction of the disulfide. This redox-switchable fluorescent Au(8) -cluster platform is a novel discovery, and its utility as a promising sensor for detecting H(2) O(2) -generating enzymatic transformations is demonstrated. 相似文献
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Huanjun Chen Zhenhua Sun Weihai Ni Kat Choi Woo Hai‐Qing Lin Lingdong Sun Chunhua Yan Jianfang Wang 《Small (Weinheim an der Bergstrasse, Germany)》2009,5(18):2111-2119
Gold nanocubes are assembled into clusters of varying numbers and ordering on indium tin oxide substrates. The plasmon coupling in the clusters is studied with both dark‐field imaging and finite‐difference time‐domain calculations. Generally, as a cluster becomes larger and more asymmetric, it exhibits more scattering peaks towards longer wavelengths. The coupling of the vertically oriented dipole in the nanocube with its image dipole in the substrate generates two scattering peaks. One is fixed in energy and the other red‐shifts with increasing cluster size. The coupling of horizontally oriented dipoles among different nanocubes produces multiple scattering peaks at lower energies. Their positions and intensities are highly dependent on the number and ordering of nanocubes in the cluster. Au nanocubes in the clusters are further welded together by thermal treatment. The scattering peaks of the thermally treated clusters generally become sharper. The lower‐energy scattering peaks arising from dipolar oscillations are red‐shifted. 相似文献