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1.
Functionalization of carbon nanotubes/graphene by polyoxometalates and their enhanced photo-electrical catalysis
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Carbon nanotubes and graphene are carbon-based materials, which possess not only unique structure but also properties such as high surface area, extraordinary mechanical properties, high electronic conductivity, and chemical stability.Thus, they have been regarded as an important material, especially for exploring a variety of complex catalysts. Considerable efforts have been made to functionalize and fabricate carbon-based composites with metal nanoparticles. In this review,we summarize the recent progress of our research on the decoration of carbon nanotubes/graphene with metal nanoparticles by using polyoxometalates as key agents, and their enhanced photo-electrical catalytic activities in various catalytic reactions. The polyoxometalates play a key role in constructing the nanohybrids and contributing to their photo-electrical catalytic properties. 相似文献
2.
In recent years, solid-state NMR spectroscopy has evolved into an important characterization tool for the study of solid catalysts and chemical processes on their surface. This interest is mainly triggered by the need of environmentally benign organic transformations (“green chemistry”), which has resulted in a large number of new catalytically active hybrid materials, which are organized on the meso- and nanoscale. Typical examples of these catalysts are supported homogeneous transition metal catalysts or transition metal nanoparticles (MNPs). Solid-state NMR spectroscopy is able to characterize both the structures of these materials and the chemical processes on the catalytic surface. This article presents recent trends both on the characterization of immobilized homogeneous transition metal catalysts and on the characterization of surface species on transition metal surfaces. 相似文献
3.
Pomogailo Anatolii D. Dzhardimalieva Gulzhian I. Rozenberg Aleksander S. Muraviev Dmitri N. 《Journal of nanoparticle research》2003,5(5-6):497-519
The kinetic peculiarities of the thermal transformations of unsaturated metal carboxylates (transition metal acrylates and maleates as well as their cocrystallites) and properties of metal-polymer nanocomposites formed have been studied. The composition and structure of metal-containing precursors and the products of the thermolysis were identified by X-ray analysis, optical and electron microscopy, magnetic measurements, EXAFS, IR and mass spectroscopy. The thermal transformations of metal-containing monomers studied are the complex process including dehydration, solid phase polymerization, and thermolysis process which proceed at varied temperature ranges. At 200–300°C the rate of thermal decay can be described by first-order equations. The products of decompositions are nanometer-sized particles of metal or its oxides with a narrow size distribution (the mean particle diameter of 5–10nm) stabilized by the polymer matrix. 相似文献
4.
《Surface science》1986,167(1):231-260
Surface plasmon (SP) effects on the optical properties of rough metal surfaces are considered. Angular and frequency dependences of radiation, arising from SP decay and diffuse light scattering, as well as the photoemission current from a rough metal surface have been calculated. The above effects have been shown to be strongly enhanced when SP attenuation lengths stipulated by SP decay into vacuum and absorption in the metal, are much larger than the attenuation length stipulated by transformations into other SP states. Possibilities of comparing theoretical calculations with experimental data are considered. 相似文献
5.
Photoinduced transformations of CuTCNQ and AgTCNQ films, and several metal TCNQ salts with visible light have been observed and studied by Raman spectroscopy. Both partial and complete transformations, leading to metal and TCNQ in various material forms, are affected, and implications for photoswitching and light writing discussed. 相似文献
6.
多金属氧酸盐(简称多酸,Polyoxometalates,POMs)是由处于d0电子构型的前过渡金属元素通过共边或共角缩聚而成的金属-氧簇类化合物.由于其具有丰富的分子结构和独特的物理化学性质,已经被广泛应用于功能材料、催化化学和药物化学等领域.其中钒取代的多酸阴离子具有很好的催化活性,特别是对烃类的氧化,它的活性主要受钒取代的数目和钒中心的阴离子环境这两个因素影响.该文利用固体核磁技术分析了一取代钒的两类典型结构中51V的局域结构和化学环境,以及有机阳离子对多酸阴离子结构的影响,特别是对51V的化学环境的影响,为研究多酸的催化活性和催化机理提供基本的结构信息. 相似文献
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8.
J. V. Kasiuk J. A. Fedotova M. Marszalek A. Karczmarska M. Mitura-Nowak Yu. E. Kalinin A. V. Sitnikov 《Physics of the Solid State》2012,54(1):178-184
The elemental and phase compositions and the magnetic state of metal particles in FeCoZr-Pb(ZrTi)O3 granular nanocomposites (GNCs) synthesized by ion-beam sputtering of composite targets in oxygen-containing media at different
oxygen partial pressures have been studied. The phase transformations in GNCs have been monitored by the Raman and M?ssbauer
spectroscopy techniques. Correlation between the oxygen pressure during GNC synthesis and the valence state of iron ions in
metal granules has been established. It has been confirmed that (i) the degree of metal oxidation increases with increasing
oxygen pressure and (ii) the degree of crystallinity of oxides increases as a result of annealing. It has been established
that the percolation threshold in GNCs can also be varied by changing the oxygen pressure during GNC synthesis. 相似文献
9.
Xiaoyi Xie Yi Zhang Dong Li Yuxiu Fan Bin Huang Xiupei Yang 《Particle & Particle Systems Characterization》2023,40(10):2300039
Nanozymes can be used as favorable substitutes for natural enzymes because of their strong catalytic activity and good stability. At the same time, research on single-atom catalysts (SACs) with isolated metal atoms as active centers is also in full swing, showing excellent performance in a variety of catalytic reactions. With the in-depth study of SACs, people have a comprehensive understanding of them and put forward the concept of single-atom nanozymes (SAzymes) by combining nanozymes with SACs. As a new type of nanomaterial, SAzymes have attracted great interest due to their remarkable catalytic activity and rapid energy conversion. However, most applications of SAzymes are mainly in the fields of biomedicine and biosensing, and less research has been done in the field of the environment. Based on the amazing ability of nanozymes to detect and degrade pollutants, SAzymes are also used in the environmental field, and even they will show better capabilities. This review mainly analyses common transition metal-based SAzymes and describes their applications in the field of environmental pollutants. 相似文献
10.
Alan L. Stottlemyer Thomas G. Kelly Qinghe Meng Jingguang G. Chen 《Surface Science Reports》2012,67(9-10):201-232
Historically the interest in the catalytic properties of transition metal carbides (TMC) has been inspired by their “Pt-like” properties in the transformation reactions of hydrocarbon molecules. Recent studies, however, have revealed that the reaction pathways of oxygen-containing molecules are significantly different between TMCs and Pt-group metals. Nonetheless, TMCs demonstrate intriguing catalytic properties toward oxygen-containing molecules, either as the catalyst or as the catalytically active substrate to support metal catalysts, in several important catalytic and electrocatalytic applications, including water electrolysis, alcohol electrooxidation, biomass conversion, and water gas shift reactions. In the current review we provide a summary of theoretical and experimental studies of the interaction of TMC surfaces with oxygen-containing molecules, including both inorganic (O2, H2O, CO and CO2) and organic (alcohols, aldehydes, acids and esters) molecules. We will discuss the general trends in the reaction pathways, as well as future research opportunities in surface science studies that would facilitate the utilization of TMCs as catalysts and electrocatalysts. 相似文献
11.
C. G. Vayenas S. Bebelis S. Neophytides I. V. Yentekakis 《Applied Physics A: Materials Science & Processing》1989,49(1):95-103
The catalytic activity and selectivity of metal catalysts used as electrodes in high temperature solid electrolyte cells can be altered dramatically and in a reversible manner. This is accomplished by electrochemically supplying oxygen anions onto catalytic surfaces via polarized metal-solid electrolyte interfaces. Oxygen anions, forced electrochemically to adsorb on the metal catalyst surface, alter the catalyst work function in a predictable way and lead to reaction rate increases as high as 4000%. Changes in catalytic rates typically exceed the rate of O2– transport to or from the catalyst surface by 102-3 · 105. Significant changes in product selectivity have been also observed. The case of several catalytic reactions in which this new phenomenon has been observed is presented and the origin of the phenomenon is discussed. 相似文献
12.
采用类桑拿法制备了聚苯乙烯微球模板, 结合双层Mo金属结构, 获得了具有周期性结构的Mo金属催化电极. 通控制氧气对聚苯乙烯球的刻蚀时间, 可有效调制Mo金属催化电极的横、纵向尺寸, 从而获得不同的衬底比表面积. 通过原子力显微镜表面形貌测试、电化学线性扫描、塔菲尔测试以及阻抗谱分析表明: 增大刻蚀时间可有效提高Mo金属催化电极的表面粗糙度和比表面积, 进而降低电荷传输电阻和塔菲尔斜率, 促进催化电极/电解液界面处析氢反应的进行. 采用类桑拿法和双层Mo金属结构制备周期性结构的方法简单, 可大面积化, 同时低温磁控溅射法制备的Mo金属催化电极成本低廉, 温度兼容多种太阳电池器件, 具有形成高效一体化光水解制氢器件的潜力. 相似文献
13.
Metal particle combustion and nanotechnology 总被引:3,自引:0,他引:3
Richard A. Yetter Grant A. Risha Steven F. Son 《Proceedings of the Combustion Institute》2009,32(2):1819-1838
Metal combustion has received renewed interest largely as a result of the ability to produce and characterize metallic nanoparticles. Much of the highly desirable traits of nanosized metal powders in combustion systems have been attributed to their high specific surface area (high reactivity) and potential ability to store energy in surfaces. In addition, nanosized powders are known to display increased catalytic activity, superparamagnetic behavior, superplasticity, lower melting temperatures, lower sintering temperatures, and higher theoretical densities compared to micron and larger sized materials. The lower melting temperatures can result in lower ignition temperatures of metals. The combustion rates of materials with nanopowders have been observed to increase significantly over similar materials with micron sized particles. A lower limit in size of nanoenergetic metallic powders in some cases may result from the presence of their passivating oxide coating. Consequently, coatings, self-assembled monolayers (SAMs), and the development of composite materials that limit the volume of non-energetic material in the powders have been under development in recent years. After a brief review of the classifications of metal combustion based on thermodynamic considerations and the different types of combustion regimes of metal particles (diffusion vs. kinetic control), an overview of the combustion of aluminum nanoparticles, their applications, and their synthesis and assembly is presented. 相似文献
14.
Fokker-Planck type equations have been classified according to the groups of contact transformations to which they belong.
It has been found that there are only five classes as in the case of groups of point transformations. We have also obtained
the algebraic structures of the corresponding Lie algebras. However, there are isomorphies in their group properties. The
corresponding basis sets of functionally independent invariants formed by the generators of these groups have also been obtained. 相似文献
15.
Structural-phase transformations in surface layers of iron and Fe? Cr? (Ni) alloys subjected to ion-plasma nitriding and subsequent cold plastic compression shear deformation in Bridgman anvils have been investigated by the methods of Mössbauer spectroscopy, transmission electron microscopy and X-ray analysis. It has been shown that the deformation-induced cyclic phase “dissolution–precipitation” transformations of nitrides in alloys lead to the formation of nitrogen oversaturated solid solutions, precipitation of secondary nitrides and nanostructurization of the metal matrix. 相似文献
16.
M. Gruyters T. Mitrelias D. A. King 《Applied Physics A: Materials Science & Processing》1995,61(3):243-251
A synopsis of the recent developments in acoustically influencing and controlling gas-surface interactions is presented. The cleaning effect of ultrasound and its surface activation play an important role for the sonochemical enhancement of reactivity in chemical processes involving solid and liquid phases. So far, there have only been a few studies on the effects of surface acoustic waves on surface chemical reactions under high-vacuum conditions by the application of piezoelectric surface acoustic wave transducers. Very recently, metal films deposited between InterDigital Transducer (IDT) electrodes on a LiNbO3 substrate have shown a significant inerease in catalytic activity during surface acoustic excitation and Edge-Bonded Transducers (EBT) with a metal single crystal as a substrate have been used to acoustically influence the rate in the oscillatory reaction for CO oxidation. Tunable narrowband surface acoustic excitation is anticipated to be an efficient route to control catalytic processes, and in our work this approach is being used to investigate the physical basis of this process. 相似文献
17.
18.
Metal-oxide interfaces are of great importance in catalytic applications since each material can provide a distinct functionality that is necessary for efficient catalysis in complex reaction pathways. Moreover, the synergy between two materials can yield properties that exceed the superposition of single sites. While interfaces between metals and metal oxides can play a key role in the reactivity of traditional supported catalysts, significant attention has recently been focused on using “inverted” oxide/metal catalysts to prepare catalytic interfaces with unique properties. In the inverted systems, metal surfaces or nanoparticles are covered by oxide layers ranging from submonolayer patches to continuous films with thickness at the nanometer scale. Inverse catalysts provide an alternative approach for catalyst design that emphasizes control over interfacial sites, including inverted model catalysts that provide an important tool for elucidation of mechanisms of interfacial catalytic reactions and oxide-coated metal nanoparticles that can yield improved stability, activity and selectivity for practical catalysts.This review begins by providing a summary of recent progress in the use of inverted model catalysts in surface science studies, where oxides are usually deposited onto the surface of metal single crystals under ultra-high vacuum conditions. Surface-level studies of inverse systems have yielded key insights into interfacial catalysis and facilitated active site identification for important reactions such as CO oxidation, the water-gas shift reaction, and CO2 reduction using well-defined model systems, informing strategies for designing improved technical catalysts. We then expand the scope of inverted catalysts, using the “inverse” strategy for preparation of higher-surface area practical catalysts, chiefly through the deposition of metal oxide films or particles onto metal nanoparticles. The synthesis techniques include encapsulation of metal nanoparticles within porous oxide shells to generate core-shell type catalysts using wet chemical techniques, the application of oxide overcoat layers through atomic layer deposition or similar techniques, and spontaneous formation of metal oxide coatings from more conventional catalyst geometries under reaction or pretreatment conditions. Oxide-coated metal nanoparticles have been applied for improvement of catalyst stability, control over transport or binding to active sites, direct modification of the active site structure, and formation of bifunctional sites. Following a survey of recent studies in each of these areas, future directions of inverted catalytic systems are discussed. 相似文献
19.
Mohamed A. Shenashen Sherif A. El‐Safty Emad A. Elshehy 《Particle & Particle Systems Characterization》2014,31(3):293-316
Nanostructured materials, especially nanoparticles (NPs), of noble metal NPs such as silver (Ag) have been the focus of research in recent decades because of their distinct physical, chemical, and biological properties. These materials have attracted considerable attention because of their potential applications, such as catalysis, biosensing, drug delivery, and nanodevice fabrication. Previous studies on Ag NPs have clearly demonstrated that their electromagnetic, optical, and catalytic properties are strongly influenced by their shape, size, and size distribution, which can be varied by using different synthetic methods, reducing agents, and stabilizers. The valuable optical properties of Ag NPs have allowed for new approaches in sensing and imaging applications, offering a wide range of detection modes, such as colorimetric, scattering, and surface‐enhanced Raman scattering techniques, at extremely low detection limits. Here, an overview of the various chemical, physical, and biological properties of Ag NP fabrication approaches to obtain the various shapes and sizes is presented. 相似文献
20.
M. Yu. Sinev 《Russian Journal of Physical Chemistry B, Focus on Physics》2007,1(4):412-433
An approach to modeling catalytic oxidative transformations of light alkanes (LAs) based on the use of thermochemical data
is developed. The fact that LAs are virtually not adsorbed on the surface of oxidation catalysts seriously limits the possibility
of experimentally studying the mechanisms of their transformations. In addition, LAs, the least reactive organic compounds,
are oxidized at elevated temperatures even on the most active catalysts, a circumstance that makes the contribution from the
homogeneous process to the overall conversion rate significant. For this reason, it is necessary to develop multilevel models
capable of describing of the elementary reactions of LAs and intermediate products of their transformations (including free
radicals of various types) with active sites of catalysts as well as the process as a whole. The proposed approach, based
on the experimental data on the thermochemical properties of redox active sites, is applicable to describing processes occurring
in the presence of an oxide catalyst. It makes it possible to estimate the kinetic parameters of the elementary interactions
of molecules and radicals with active sites in reduced and oxidized states, that is, to solve the problem of the initial stage
of modeling of a multistep process. A number of examples of applying this approach to studying oxidative transformations (partial
oxidation and oxidative coupling) of methane, oxidative dehydrogenation of C2–C4 alkanes, and reoxidation of catalysts are considered. The prospects of modeling the heterogeneous-homogeneous oxidation of
light alkanes are discussed. 相似文献