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1.
Jyoti Lather Pooja Bhatt Anoop Thomas Thomas W. Ebbesen Jino George 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(31):10745-10748
Here, we report the catalytic effect of vibrational strong coupling (VSC) on the solvolysis of para‐nitrophenyl acetate (PNPA), which increases the reaction rate by an order of magnitude. This is observed when the microfluidic Fabry–Perot cavity in which the VSC is generated is tuned to the C=O vibrational stretching mode of both the reactant and solvent molecules. Thermodynamic experiments confirm the catalytic nature of VSC in the system. The change in the reaction rate follows an exponential relation with respect to the coupling strength of the solvent, indicating a cooperative effect between the solvent molecules and the reactant. Furthermore, the study of the solvent kinetic isotope effect clearly shows that the vibrational overlap of the C=O vibrational bands of the reactant and the strongly coupled solvent molecules is critical for the catalysis in this reaction. The combination of cooperative effects and cavity catalysis confirms the potential of VSC as a new frontier in chemistry. 相似文献
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固体酸催化剂广泛应用于现代石油与化学工业中,其反应活性与其酸性密切相关.与传统的酸性表征方法(红外光谱、程序升温脱附、滴定等)相比,利用先进的探针分子技术、双共振和二维相关谱等核磁共振(NMR)技术可以获取固体催化剂酸种类、酸分布、酸浓度和酸强度等完整信息.同时,原位固体NMR实验可跟踪反应分子在催化剂活性中心吸附状态和转换的中间体物种,为揭示反应机理提供了最直接的实验证据.本文详细介绍了固体NMR的原理和一系列相关新技术,着重综述了固体NMR技术在酸催化剂结构、活性中心特性以及催化反应机理方面的应用进展. 相似文献
3.
V. F. Kharlamov 《Kinetics and Catalysis》2005,46(4):464-471
In some heterogeneous chemical processes occurring on the solid/gas interface, reactant atoms and molecules chemisorbed during the reaction are not directly involved in chemical transformations but act as catalytic sites accelerating this reaction.__________Translated from Kinetika i Kataliz, Vol. 46, No. 4, 2005, pp. 497–505.Original Russian Text Copyright © 2005 by Kharlamov. 相似文献
4.
碱木质素在超临界水中Ru/C纳米管催化气化的降解研究 《燃料化学学报》2015,43(10):1195-1201
针对碱木质素难降解的特点,在间歇式反应器中,以Ru/C纳米管为催化剂,对碱木质素在超临界水中的气化进行研究。分别探讨了碱木质素在不同温度、水密度、反应时间、反应浓度、催化剂量的影响,并且分析了Ru/C纳米管催化剂的催化效率。通过单因素实验分析,确定了Ru/C纳米管催化剂催化气化碱木质素的最佳反应条件为,反应温度600 ℃、水密度0.128 4 g/cm3、反应时间60 min、反应质量分数3.0%、催化剂量0.5 g/g(碱木质素)。结果表明,碱木质素在超临界水气化过程中,高温、高水密度(或压力)、长反应时间、低反应物浓度及适量的催化剂将更有利于碱木质素的气化。在最佳反应条件下碱木质素的气化率和碳气化率分别达到73.74%和56.34%,且制氢能力也得到明显提高。 相似文献
5.
Expansion of the Concept of Nonlinear Effects in Catalytic Reactions Beyond Asymmetric Catalysis
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Dipl.‐Ing. Robert Pollice Prof. Dr. Michael Schnürch 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(16):5637-5642
The observation and investigation of nonlinear effects in catalytic reactions provides valuable mechanistic insight. However, the applicability of this method was, until now, limited to molecules possessing chirality and therefore to asymmetric synthesis. The concept of nonlinear effects is expanded to catalytic reactions beyond asymmetric catalysis by using derivatives instead of enantiomers and by considering rates instead of enantiomeric excess. Additionally, its systematic application to investigate the mechanism of catalytic reactions is presented. By exceeding the limitation to asymmetric reactions, the study of nonlinear effects can become a general tool to elucidate reaction mechanisms. 相似文献
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Thomas V. PREVENSLIK 《催化学报》2008,29(11)
Gold has been regarded as a poor heterogeneous catalyst because it is generally considered a nonreactive metal. But as nanocatalysts,gold and other metals somehow significantly enhance reactivity. It is generally thought chemical bonds of reactants are weakened by adsorption to nanocatalysts thereby allowing reactions to proceed more rapidly,but how this reaction proceeds to completion is not well understood. Here gold nanocatalysts are treated as unsupported nanoparticles (NPs) in a solution of reactant molecules from which extensions are made to gold NPs supported on titanium dioxide. Whether the NPs are supported or unsupported,enhanced catalytic reactivity depends on absorbed thermal kT (k is Boltzmann's constant and T is absolute temperature) energy accumulated from prior collisions of reactant molecules. The accumulated kT energy is treated as electromagnetic thereby allowing frequency up-conversion by quantum electrodynamics (QED) to the confinement frequency of the NP,typically beyond the vacuum ultraviolet (VUV). By this theory,the chemical reaction of reactant molecules having bonds weakened by adsorption is completed by QED induced VUV photolysis. 相似文献
8.
Microwave irradiation does not accelerate the rate of the Perkin reaction carried out under normal atmospheric pressure. Water is an essential yet catalytic reactant for the Perkin reaction to occur. Containment of the Perkin reaction in a sealed vessel improves the yield. Two pressure increases are observed during a 4 h reaction time. An induction period is seen in the Perkin reaction when sodium acetate is used as a base. A re-appraisal of the reaction mechanism is proposed on the basis of these observations. The use of PFA® reaction vessels enables the Perkin reaction to occur under aqueous conditions for around 80 reactions/vessel. 相似文献
9.
In/SBA-15催化剂的一步法制备及其在水介质中Barbier反应中的应用 总被引:1,自引:0,他引:1
采用金属In的石蜡溶液浸渍载体, 一步法制备具有介孔结构的In/SBA-15催化剂. 在水介质中苯甲醛与烯丙基溴的Barbier反应中, 发现负载量为w(In)=13%的In/SBA-15的催化活性显著高于金属In颗粒催化剂, 而选择性相似, 目标产物1-苯基-3-丁烯基-1-醇的得率可达89.2%. In/SBA-15的高活性主要归因于In活性位在SBA-15上的高分散, 以及规整的介孔结构有利于反应物分子的扩散. 同时, 金属In与SBA-15间较强的相互作用也可稳定In活性位, 显示出良好的应用潜力. 相似文献
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Dr. Carmine D'Agostino Dr. Gemma L. Brett Dr. Peter J. Miedziak Prof. David W. Knight Prof. Graham J. Hutchings Prof. Lynn F. Gladden Dr. Mick D. Mantle 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(45):14426-14433
The effect of water on the catalytic oxidation of 1,4‐butanediol in methanol over Au/TiO2 has been investigated by catalytic reaction studies and NMR diffusion and relaxation studies. The addition of water to the dry catalytic system led to a decrease of both conversion and selectivity towards dimethyl succinate. Pulsed‐field gradient (PFG)‐NMR spectroscopy was used to assess the effect of water addition on the effective self‐diffusivity of the reactant within the catalyst. NMR relaxation studies were also carried out to probe the strength of surface interaction of the reactant in the absence and presence of water. PFG‐NMR studies revealed that the addition of water to the initial system, although increasing the dilution of the system, leads to a significant decrease of effective diffusion rate of the reactant within the catalyst. From T1 and T2 relaxation measurements it was possible to infer the strength of surface interaction of the reactant with the catalyst surface. The addition of water was found to inhibit the adsorption of the reactant over the catalyst surface, with the T1/T2 ratio of 1,4‐butanediol decreasing significantly when water was added. The results overall suggest that both the decrease of diffusion rate and adsorption strength of the reactant within the catalyst, due to water addition, limits the access of reactant molecules to the catalytic sites, which results in a decrease of reaction rate and conversion. 相似文献
13.
In our invention, FCC (fluid catalytic cracking) dry gas could be used to react with benzene without any special purification, and more than 90% ethylene was converted to ethylbenzene. The phenomenon of carbon deposition over catalyst surface was obvious and leads to a deactivation of catalyst, so it is important to study the behavior of carbon deposition of catalyst during alkylation of benzene. The influence of several factors such as temperature, reaction time, reactant concentration of the amount and the kinetics of carbon deposition were investigated, during which carbon depositing rate equations were obtained for different reactant.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
14.
WANG Yitong MENG Fanchen SU Ruifa SUN Changrui HAN Qianqian ZHANG Weina ZHANG Suoying 《高等学校化学研究》2022,38(6):1356-1360
Metal-organic frameworks(MOFs) have been widely regarded as promising carriers for enzyme immobilization owing to their advantages in improving loading and regulating interaction with enzymes. However, they are still suffering from the problems of slow mass transfer and compromising activity. In this paper, the active two-dimensional(2D) MOF of Cu-TCPP(Fe)[TCPP=tetrakis(4-carboxy-phenyl)porphyrin], which possesses the biomimetic architecture of peroxidase, was adopted to anchor cytochrome(Cyt c) for the enhancement of catalytic activity. The atomic/nanometer thickness and micrometer lateral dimension of 2D MOFs can ensure the full exposure of immobilized enzymes and a shorter diffusion distance for the reactant molecules. Besides, the active carrier can provide synergistic catalysis and activity compensation during the reaction. When tested in the decomposition reaction of H2O2, Cyt c/Cu-TCPP(Fe) exhibited nearly twice catalytic activity and an accelerated catalytic rate compared to free Cyt c. 相似文献
15.
B. Samori S. Masiero G. R. Luckhurst S. K. Heeks B. A. Timimi P. Mariani 《Liquid crystals》1993,15(2):217-231
The rearrangement of allyl p-dimethylaminobenzenesulphonate (ASE) to form a zwitterionic product has already been recognized as an effective probe for the study of reactivity within the smectic B phase [4, 5, 19]. We have used deuterium NMR, linear dichroism and X-ray diffraction techniques to investigate the phase diagram of the ASE-OS35 reaction system. The partitioning of the reactant molecules between coexisting smectic, nematic and/or isotropic phases and the structural organization of the smectic catalytic host at different temperatures and reactant guest concentrations have been characterized. On the basis of these measurements, a model of ASE reactivity in smectic solvents has been developed. The reaction takes place provided that coexisting isotropic or nematic phases are present to act as a reservoir for the ASE reactant molecules prior to their entering the smectic phase; they then react and leave the smectic phase as a zwitterionic product. The analogy between this model of reactivity within smectic phases and the Michaelis-Menten enzyme processes is discussed. This relationship opens up the intriguing possibility of designing new experiments with which to investigate further liquid crystalline models of enzyme catalysis. 相似文献
16.
We report a type of highly efficient double hydrogen atom transfer (DHAT) reaction. The reactivities of 3-aminopropanol and 2-aminoethanol towards Criegee intermediates (syn- and anti-CH3CHOO) were found to be much higher than those of n-propanol and propylamine. Quantum chemistry calculation has confirmed that the main mechanism of these very rapid reactions is DHAT, in which the nucleophilic attack of the NH2 group is catalyzed by the OH group which acts as a bridge of HAT. Typical gas-phase DHAT reactions are termolecular reactions involving two hydrogen bonding molecules; these reactions are typically slow due to the substantial entropy reduction of bringing three molecules together. Putting the reactive and catalytic groups in one molecule circumvents the problem of entropy reduction and allows us to observe the DHAT reactions even at low reactant concentrations. This idea can be applied to improve theoretical predictions for atmospherically relevant DHAT reactions. 相似文献
17.
Prof. James H. Clark Dr. Duncan J. Macquarrie James Sherwood 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(16):5174-5182
The traditional Biginelli reaction is a three‐component condensation between urea, benzaldehyde and an acetoacetate ester to give a dihydropyrimidinone. An investigation into catalytic and solvent effects has returned the conclusion that the diketo–enol tautomerisation equilibrium of the dicarbonyl reactant dictates the yield of the reaction. Whereas the solvent is responsible for the tautomerisation equilibrium position, the catalyst only serves to eliminate kinetic control from the reaction. Generally, to preserve reaction efficiency and improve sustainability, bio‐derivable p‐cymene was found to be a useful solvent. The metal–enolate intermediate that results from the application of a Lewis acidic catalyst often cited as promoting the reaction appears to hinder the reaction. In this instance, a Brønsted acidic solvent can be used to return greater reactivity to the dicarbonyl reagent. 相似文献
18.
Stavitski E Kox MH Weckhuysen BM 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(25):7057-7065
A combination of in-situ optical and fluorescence microspectroscopy has been employed to investigate the oligomerization of styrene derivatives occurring in the micropores of coffin-shaped H-ZSM-5 zeolite crystals in a space- and time-resolved manner. The carbocationic intermediates in this reaction act as reporter molecules for catalytic activity, since they exhibit strong optical absorption and fluorescence. In this way, reactant selectivity and restricted transition-state selectivity for 14 substituted styrene molecules can be visualized and quantified. Based on a thorough analysis of the time- and space-resolved UV/Vis spectra, it has been revealed that two main parameters affect the reaction rates, namely, the carbocation stabilization effect and the diffusion hindrance. The stabilization effect was tested by comparison of the reaction rates for 4-methoxystyrene versus 4-methylstyrene and in the series 4-bromo-, 4-chloro and 4-fluorostyrene; in both cases less electronegative substituents were found to accelerate the reaction. As to the steric effect, bulkier chemical groups bring down the reaction rate, as evident from the observation that 4-methoxystyrene is more reactive than 4-ethoxystyrene due to differences in their diffusivity, while heavily substituted styrenes, such as 3,4-dichlorostyrene and 2,3,4,5,6-pentafluorostyrene, cannot enter the zeolite pore system and therefore do not display any reactivity. Furthermore, beta-methoxystyrene and trans-beta-methylstyrene show limited reactivity as well as restricted reaction-product formation due to steric constraints imposed by the H-ZSM-5 channel system. Finally, polarized-light optical microspectroscopy and fluorescence microscopy demonstrate that dimeric styrene compounds are predominantly formed and aligned within the straight channels at the edges of the crystals, whereas a large fraction of trimeric carbocations along with dimeric compounds are present in the straight channels of the main body of the H-ZSM-5 crystals. Our results reinforce the observation of a non-uniform catalytic behavior within zeolite crystals, with specific parts of the zeolite grains being less accessible and reactive towards reactant molecules. The prospects and potential of this combined in-situ approach for studying large zeolite crystals in the act will be discussed. 相似文献
19.
Dinuclear Copper Intermediates in Copper(I)‐Catalyzed Azide–Alkyne Cycloaddition Directly Observed by Electrospray Ionization Mass Spectrometry
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Dr. Claudio Iacobucci Dr. Samantha Reale Prof. Jean‐François Gal Prof. Francesco De Angelis 《Angewandte Chemie (International ed. in English)》2015,54(10):3065-3068
The mechanism of the CuAAC reaction has been investigated by electrospray ionization mass spectrometry (ESI‐MS) using a combination of the neutral reactant approach and the ion‐tagging strategy. Under these conditions, for the first time, putative dinuclear copper intermediates were fished out and characterized by ESI(+)‐MS/MS. New insight into the CuAAC reaction mechanisms is provided and a catalytic cycle is proposed. 相似文献
20.
Dr. Adrián Gómez‐Suárez Dr. Yoshihiro Oonishi Dr. Anthony R. Martin Dr. Sai V. C. Vummaleti Dr. David J. Nelson Dr. David B. Cordes Prof. Alexandra M. Z. Slawin Prof. Dr. Luigi Cavallo Prof. Dr. Steven P. Nolan Dr. Albert Poater 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(3):1125-1132
Herein, we present a detailed investigation of the mechanistic aspects of the dual gold‐catalysed hydrophenoxylation of alkynes by both experimental and computational methods. The dissociation of [{Au(NHC)}2(μ‐OH)][BF4] is essential to enter the catalytic cycle, and this step is favoured by the presence of bulky, non‐coordinating counter ions. Moreover, in silico studies confirmed that phenol does not only act as a reactant, but also as a co‐catalyst, lowering the energy barriers of several transition states. A gem‐diaurated species might form during the reaction, but this lies deep within a potential energy well, and is likely to be an “off‐cycle” rather than an “in‐cycle” intermediate. 相似文献