Metal nanoparticles (NPs) find widespread application as a result of their unique physical and chemical properties. NPs have generated considerable interest in catalysis and electrocatalysis, where they provide a high surface area to mass ratio and can be tailored to promote particular reaction pathways. The activity of NPs can be analyzed especially well using electrochemistry, which probes interfacial chemistry directly. In this Review, we discuss key issues related to the electrochemistry of NPs. We highlight model studies that demonstrate exceptional control over the NP shape and size, or mass‐transport conditions, which can provide key insights into the behavior of ensembles of NPs. Particular focus is on the challenge of ultimately measuring reactions at individual NPs, and relating the response to their structure, which is leading to imaginative experiments that have an impact on electrochemistry in general as well as broader surface and colloid science. 相似文献
In this paper we discuss a general framework for single component replacement models. This framework is based on the regenerative structure of these models and by using results from renewal theory a unified presentation of the discounted and average finite and infinite horizon cost models is given. Finally, some well-known replacement models are discussed, and making use of the previous results an easy derivation of their cost functions is presented. 相似文献
Epimestranol () is obtained in 80% yield from mestranol () by converting into its methanesulfonate and treating with silver(I) nitrate in a mixture of tetrahydrofuran and water. 相似文献
The enynyl oxiranes (I) react with alkylsilver compounds to form butatrienyl carbinols RCH2C(Me)CCC(R′)CR″2OH (IV,V). Alkylcopper reagents, on the other hand, preferentially convert I into allenyl carbinols H2CC(Me)C(R)CC(R′)CR″2OH (III) 相似文献
The paper describes new routes to aryl-, vinyl-, and 1-alkynylallenes and to diallenes Pd(PPh3)4-promoted reaction of propargylic or allenic halides with appropriate organozinc halides. Propargylic acetates are also suited to prepare such allenes. 相似文献
Allenyl-germanes and -stannanes, Ph3MC(R)CCR′R″ (M = Ge, Sn) can be obtained, generally in excellent yield, through alkylcopper(I)-induced 1,3-substitution of the propargylic chlorides Ph3MCCCR′R″Cl. In the tin series, however transmetallation is the main process when MeCu, H2CCHCu or PhCu are used. The allenyl compounds in which R is (trimethylsilyl)ethynyl or 4,4-dimethyl-1,2-pentadienyl can be obtained by using the organozinc compounds instead of the copper(I) compound and using tetrakis(triphenylphosphine)palladium as catalyst. 相似文献
We describe the use of a polished, hollow cylindrical nickel single crystal to study effects of step edges on adsorption and desorption of gas phase molecules. The crystal is held in an ultra-high vacuum apparatus by a crystal holder that provides axial rotation about a [100] direction, and a crystal temperature range of 89 to 1100 K. A microchannel plate-based low energy electron diffraction/retarding field Auger electron spectrometer (AES) apparatus identifies surface structures present on the outer surface of the cylinder, while a separate double pass cylindrical mirror analyzer AES verifies surface cleanliness. A supersonic molecular beam, skimmed by a rectangular slot, impinges molecules on a narrow longitudinal strip of the surface. Here, we use the King and Wells technique to demonstrate how surface structure influences the dissociation probability of deuterium at various kinetic energies. Finally, we introduce spatially-resolved temperature programmed desorption from areas exposed to the supersonic molecular beam to show how surface structures influence desorption features. 相似文献
The catalytic activities of the highly fluorous systems formed by the zirconocene(IV) complexes [Zr{η5-C5H4SiMe2C2H4RF}2Cl2] (RF = C6F13 (4a), C10F21 (4b)) or [Zr-{η5-C5H3(SiMe2C2H4C6F13)2}2Cl2] (5a) and MMAO in toluene have been studied and compared with analogous nonfluorous systems generated from [Zr{η5-C5H4SiMe3}2Cl2] and [Zr{η5-C5H5}2Cl2]. Although less active than the reference systems, the fluorous catalysts are stable over prolonged polymerization times, giving rise to polymers with similar molecular weights to those obtained with [Zr{η5-C5H4SiMe3}2Cl2]. 相似文献
The general formula for the number of diagrammatic terms occurring in the Tn equation within a particular coupled cluster model is derived. Both the antisymmetrized and Goldstone diagrams are considered. In addition to the full coupled cluster equation approximate approaches are discussed, and for each the general formula for the number of terms is given. Analogous expressions are presented for the number of diagrammatic terms contributing to the elements of the transformed Hamiltonian [Hbar] = e?THeT. 相似文献