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Size of Gold Nanoparticles Driving Selective Amide Synthesis through Aerobic Condensation of Aldehydes and Amines 下载免费PDF全文
Dr. Hiroyuki Miyamura Hyemin Min Dr. Jean‐François Soulé Prof. Dr. Shū Kobayashi 《Angewandte Chemie (International ed. in English)》2015,54(26):7564-7567
Metal nanoparticles (NPs) have attracted much attention in many fields due to their intrinsic characteristics. It is generally accepted that smaller NPs (1.5–3 nm) are more active than larger NPs, and reverse cases are very rare. We report here the direct aerobic oxidative amide synthesis from aldehydes and amines catalyzed by polymer‐incarcerated gold (Au) NPs. A unique correlation between imine/amide selectivity and size of NPs was discovered; Au‐NPs of medium size (4.5–11 nm) were found to be optimal. High yields were obtained with a broad range of substrates, including primary amines. Au‐NPs of medium size could be recovered and reused several times without loss of activity, and they showed good activity and selectivity in amide formation from alcohols and amines. 相似文献
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Dr. Roberto Martin Dr. Sergio Navalon Dr. Juan Jose Delgado Dr. Jose J. Calvino Prof. Mercedes Alvaro Prof. Hermenegildo Garcia 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(34):9494-9502
The catalytic activity of diamond‐supported gold nanoparticle (Au/D) samples prepared by the deposition/precipitation method have been correlated as a function of the pH and the reduction treatment. It was found that the most active material is the one prepared at pH 5 followed by subsequent thermal treatment at 300 °C under hydrogen. TEM images show that Au/D prepared under optimal conditions contain very small gold nanoparticles with sizes below 2 nm that are proposed to be responsible for the catalytic activity. Tests of productivity using large phenol (50 g L ?1) and H2O2 excesses (100 g L ?1) and reuse gives a minimum TON of 458,759 moles of phenol degraded per gold atom. Analysis of the organic compounds extracted from the deactivated solid catalyst indicates that the poisons are mostly hydroxylated dicarboxylic acids arising from the degradative oxidation of the phenyl ring. By determining the efficiency for phenol degradation and the amount of O2 evolved two different reactions of H2O2 decomposition (the Fenton reaction at acidic pH values and spurious O2 evolution at basic pH values) are proposed for Au/D catalysis. The activation energy of the two processes is very similar (ranging between 30 and 35 kJ mol?1). By using dimethylsulfoxide as a radical scavenger and N‐tert‐butyl‐α‐phenylnitrone as a spin trap under aerated conditions, the EPR spectrum of the expected PBN? OCH3 adduct was detected, supporting the generation of HO., characteristic of Fenton chemistry in the process. Phenol degradation, on the other hand, exhibits the same activation energy as H2O2 decomposition at pH 4 (due to the barrierless attack of HO. to phenol), but increases the activation energy gradually up to about 90 kJ mol?1 at pH 7 and then undergoes a subsequent reduction as the pH increases reaching another minimum at pH 8.5 (49 kJ mol?1). 相似文献
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甲烷氧化菌素(methanobactin,mb)是具有过氧化氢还原酶活性的荧光肽.从甲基弯菌Methylosinus trichospo-rium IMV3011限铜培养介质中分离mb,采用紫外可见全波长扫描法观察mb催化对苯二酚还原氯金酸合成纳米金的作用和影响,当mb/氯金酸/对苯二酚反应液中mb的浓度分别是2.5×10-5mol/L、5.0×10-5mol/L和1.0×10-4mol/L时,形成的纳米金溶液的特征峰分别是561.5 nm(OD561=0.158)、548.0 nm(OD5 48=0.426)、536.5 nm(OD5 36=0.541),特征峰波长减小,对应的吸光值增大,表明mb能够催化对苯二酚还原氯金酸合成纳米金,并且可以通过调控mb的浓度控制纳米金的合成量及粒径大小. 相似文献
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Daniel Loof Oliver Thüringer Dr. Marco Schowalter Dr. Christoph Mahr Anmona Shabnam Pranti Prof. Dr. Walter Lang Prof. Dr. Andreas Rosenauer Dr. Volkmar Zielasek Dr. Sebastian Kunz Prof. Dr. Marcus Bäumer 《ChemistryOpen》2021,10(7):697-712
Porous networks of Pt nanoparticles interlinked by bifunctional organic ligands have shown high potential as catalysts in micro-machined hydrogen gas sensors. By varying the ligand among p-phenylenediamine, benzidine, 4,4‘‘-diamino-p-terphenyl, 1,5-diaminonaphthalene, and trans-1,4-diaminocyclohexane, new variants of such networks were synthesized. Inter-particle distances within the networks, determined via transmission electron microscopy tomography, varied from 0.8 to 1.4 nm in accordance with the nominal length of the respective ligand. While stable structures with intact and coordinatively bonded diamines were formed with all ligands, aromatic diamines showed superior thermal stability. The networks exhibited mesoporous structures depending on ligand and synthesis strategy and performed well as catalysts in hydrogen gas microsensors. They demonstrate the possibility of deliberately tuning micro- and mesoporosity and thereby transport properties and steric demands by choice of the right ligand also for other applications in heterogeneous catalysis. 相似文献
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A Simple and Fast Aqueous‐Phase Synthesis of Ultra‐Highly Concentrated Silver Nanoparticles and Their Catalytic Properties 下载免费PDF全文
Aasim Shahzad Prof. Dr. Minsub Chung Prof. Dr. Taekyung Yu Prof. Dr. Woo‐Sik Kim 《化学:亚洲杂志》2015,10(11):2512-2517
A simple and fast synthetic route to ultra‐highly concentrated silver nanoparticles with long‐term stability by reducing AgNO3 with ascorbic acid in the presence of polyethyleneimine (PEI) as a stabilizer in an aqueous phase is reported. The concentration of silver precursor was as high as 2000 mm (200 g of Ag nanoparticle per liter of water) and the reaction time was less than 10 min. The resulting silver nanoparticles show long‐term stability after two months of storage at room temperature without any signs of particle aggregation or precipitation in an aqueous phase. The successful ligand exchange of PEI‐stabilized silver nanoparticles to polyethylene glycol (PEG) and polyvinylpyrrolidone (PVP) without particle aggregation is also demonstrated. In addition, the catalytic activities of silver nanoparticles stabilized by various stabilizers prepared by the ligand exchange method was investigated. The PEI‐stabilized silver nanoparticles exhibited a higher stability than those of PEG‐ and PVP‐stabilized silver nanoparticles in the diffusion‐controlled catalytic reduction of 4‐nitrophenol to 4‐aminophenol by NaBH4. 相似文献
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Dr. Tristan Doussineau Marion Santacreu Dr. Rodolphe Antoine Dr. Philippe Dugourd Wenjing Zhang Isabelle Chaduc Dr. Muriel Lansalot Dr. Franck D'Agosto Prof. Bernadette Charleux 《Chemphyschem》2013,14(3):603-609
Charging of nanoparticles through electrospray has scarcely been explored. Spherical nanometer‐sized amphiphilic block copolymer nanoparticles with diameters ranging from ~65 to ~150 nm were electrosprayed and analysed by charge detection spectrometry. Herein, we explore the charging of these micellar nano‐objects by conducting a thorough study in different solvents, including pure water, and upon the addition of “supercharging” agents. The charge (z) of micellar nanoparticles electrosprayed from water solution is compared to the Rayleigh’s limiting charge (zR) of a charged water droplet of the same dimensions. An average ratio (z/zR) of 0.6–0.65 is observed for the micellar macro‐ions, supporting the charge residue mechanism, where the number of charges available to the micellar macro‐ion is limited by the number of charges on the nanodroplet, which is a function of the surface tension of the solvent. Also we show the possibility of increasing the charging of micellar nanoparticles in the negative mode by adding organic bases (in particular piperidine) to water/methanol solutions. 相似文献
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Aneta Januszewska Dr. Grzegorz Dercz Justyna Piwowar Dr. Rafal Jurczakowski Dr. Adam Lewera 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(50):17159-17164
Small (4 nm) nanoparticles with a narrow size distribution, exceptional surface purity, and increased surface order, which exhibits itself as an increased presence of basal crystallographic planes, can be obtained without the use of any surfactant. These nanoparticles can be used in many applications in an as‐received state and are threefold more active towards a model catalytic reaction (oxidation of ethylene glycol). Furthermore, the superior properties of this material are interesting not only due to the increase in their intrinsic catalytic activity, but also due to the exceptional surface purity itself. The nanoparticles can be used directly (i.e., as‐received, without any cleaning steps) in biomedical applications (i.e., as more efficient drug carriers due to an increased number of adsorption sites) and in energy‐harvesting/data‐storage devices. 相似文献
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Wongi Jang Richard Taylor IV Pascal N. Eyimegwu Prof. Hongsik Byun Prof. Jun-Hyun Kim 《Chemphyschem》2019,20(1):70-77
Composite materials consisting of nanoscale gold particles and protective polymer shells were designed and tested as catalysts in various chemical reactions. Initially, the systematic incorporation of multiple gold nanoparticles into a poly(N-isopropylacrylamide) particle was achieved by an in situ method under light irradiation. The degree of gold nanoparticle loading, along with the structural and morphological properties, was examined as a function of the amount of initial gold ions and reducing agent. As these gold nanoparticles were physically-embedded within the polymer particle in the absence of strong interfacial interactions between the gold nanoparticles and polymer matrix, the readily-accessible surface of the gold nanoparticles with a highly increased stability allowed for their use as recyclable catalysts in oxidation, reduction, and coupling reactions. Overall, the ability to integrate catalytically-active metal nanoparticles within polymer particles in situ allows for designing novel composite materials for multi-purpose catalytic systems. 相似文献
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Mikkel Jørgensen Prof. Henrik Grönbeck 《Angewandte Chemie (International ed. in English)》2018,57(18):5086-5089
Heterogeneous catalysts are often designed as metal nanoparticles supported on oxide surfaces. Here, the relation between particle morphology and reaction kinetics is investigated by scaling relation kinetic Monte Carlo simulations using CO oxidation over Pt nanoparticles as a model reaction. We find that different particle morphologies result in vastly different catalytic activities. The activity is strongly affected by kinetic couplings between sites, and a wide site distribution generally enhances the activity. The present study highlights the role of site‐assemblies as a concept that, in addition to isolated active sites, can be used to understand catalytic reactions over nanoparticles. 相似文献
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Dr. Yanfei Wang Dr. Ankush V. Biradar Gang Wang Dr. Krishna K. Sharma Cole T. Duncan Dr. Sylvie Rangan Prof. Tewodros Asefa 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(35):10735-10743
We report a solution‐phase synthetic route to copper nanoparticles with controllable size and shape. The synthesis of the nanoparticles is achieved by the reduction of copper(II) salt in aqueous solution with hydrazine under air atmosphere in the presence of poly(acrylic acid) (PAA) as capping agent. The results suggest that the pH plays a key role for the formation of pure copper nanoparticles, whereas the concentration of PAA is important for controlling the size and geometric shape of the nanoparticles. The average size of the copper nanoparticles can be varied from 30 to 80 nm, depending on the concentration of PAA. With a moderate amount of PAA, faceted crystalline copper nanoparticles are obtained. The as‐synthesized copper nanoparticles appear red in color and are stable for weeks, as confirmed by UV/Vis and X‐ray photoemission (XPS) spectroscopy. The faceted crystalline copper nanoparticles serve as an effective catalyst for N‐arylation of heterocycles, such as the C? N coupling reaction between p‐nitrobenzyl chloride and morpholine producing 4‐(4‐nitrophenyl)morpholine in an excellent yield under mild reaction conditions. Furthermore, the nanoparticles are proven to be versatile as they also effectively catalyze the three‐component, one‐pot Mannich reaction between p‐substituted benzaldehyde, aniline, and acetophenone affording a 100 % conversion of the limiting reactant (aniline). 相似文献
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Dr. Hristiyan A. Aleksandrov Sergey M. Kozlov Dr. Swetlana Schauermann Prof. Dr. Georgi N. Vayssilov Prof. Dr. Konstantin M. Neyman 《Angewandte Chemie (International ed. in English)》2014,53(49):13371-13375
Heterogeneous catalysis is commonly governed by surface active sites. Yet, areas just below the surface can also influence catalytic activity, for instance, when fragmentation products of catalytic feeds penetrate into catalysts. In particular, H absorbed below the surface is required for certain hydrogenation reactions on metals. Herein, we show that a sufficient concentration of subsurface hydrogen, Hsub, may either significantly increase or decrease the bond energy and the reactivity of the adsorbed hydrogen, Had, depending on the metal. We predict a representative reaction, ethyl hydrogenation, to speed up on Pd and Pt, but to slow down on Ni and Rh in the presence of Hsub, especially on metal nanoparticles. The identified effects of subsurface H on surface reactivity are indispensable for an atomistic understanding of hydrogenation processes on transition metals and interactions of hydrogen with metals in general. 相似文献
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Graphene‐based composites offer enhanced catalytic performance of metal and semiconductor nanoparticles, but their development is challenging because catalytic performance strongly depends on the structure and composition of the composite. Herein we show that the catalytic performance of a nanoparticle–graphene composite is very dependent on catalyst loading, which can be optimized for simultaneous enhancement of activity and selectivity. A glassy carbon working electrode has been modified with a gold nanoparticle–graphene (Au–G) composite with a varied number of gold nanoparticles per graphene, so that the conducting property of graphene and the electrocatalytic property of the metal were effectively coupled to give the best catalytic activity and selectivity. The modified electrode was used for simultaneous electrochemical detection of a mixture of electroactive species with high sensitivity. This result shows that the catalytic performance of a graphene‐based composite is sensitive to the catalyst loading and should be optimized for the best performance. 相似文献