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1.
Adsorbed Intermediates in Oxygen Reduction on Platinum Nanoparticles Observed by In Situ IR Spectroscopy
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Dr. Simantini Nayak Dr. Ian J. McPherson Prof. Kylie A. Vincent 《Angewandte Chemie (International ed. in English)》2018,57(39):12855-12858
The sluggish kinetics of oxygen reduction to water remains a significant limitation in the viability of proton‐exchange‐membrane fuel cells, yet details of the four‐electron oxygen reduction reaction remain elusive. Herein, we apply in situ infrared spectroscopy to probe the surface chemistry of a commercial carbon‐supported Pt nanoparticle catalyst during oxygen reduction. The IR spectra show potential‐dependent appearance of adsorbed superoxide and hydroperoxide intermediates on Pt. This strongly supports an associative pathway for oxygen reduction. Analysis of the adsorbates alongside the catalytic current suggests that another pathway must also be in operation, consistent with a parallel dissociative pathway. 相似文献
2.
Reducing frustration: The reaction of Mes(3) P(CO(2) )(AlI(3) )(2) in the presence of a CO(2) atmosphere results in the formation of Mes(3) P(CO(2) )(O(AlI(2) )(2) )(AlI(3) ) and [Mes(3) PI][AlI(4) ] (Mes=2,4,6-Me(3) C(6) H(2) ) with the evolution of CO. 相似文献
3.
Synthesis of Difluoromethyl Thioethers from Difluoromethyl Trimethylsilane and Organothiocyanates Generated In Situ
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Bilguun Bayarmagnai Christian Matheis Dr. Kévin Jouvin Prof. Dr. Lukas J. Goossen 《Angewandte Chemie (International ed. in English)》2015,54(19):5753-5756
A copper‐CF2H complex generated in situ from copper thiocyanate and TMS? CF2H smoothly converts organothiocyanates into valuable difluoromethyl thioethers. This reaction step can be combined with several thiocyanation methods to one‐pot protocols, allowing late‐stage difluoromethylthiolations of widely available alkyl halides and arenediazonium salts. This strategy enables the introduction of difluoromethylthio groups—a largely unexplored substituent with highly promising properties—into drug‐like molecules. 相似文献
4.
Direct In Situ Investigation of Milling Reactions Using Combined X‐ray Diffraction and Raman Spectroscopy
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M. Sc. Lisa Batzdorf Dipl.‐Chem. Franziska Fischer Dipl.‐Chem. Manuel Wilke Dipl.‐Ing. Klaus‐Jürgen Wenzel Dr. Franziska Emmerling 《Angewandte Chemie (International ed. in English)》2015,54(6):1799-1802
The combination of two analytical methods including time‐resolved in situ X‐ray diffraction (XRD) and Raman spectroscopy provides a new opportunity for a detailed analysis of the key mechanisms of milling reactions. To prove the general applicability of our setup, we investigated the mechanochemical synthesis of four archetypical model compounds, ranging from 3D frameworks through layered structures to organic molecular compounds. The reaction mechanism for each model compound could be elucidated. The results clearly show the unique advantage of the combination of XRD and Raman spectroscopy because of the different information content and dynamic range of both individual methods. The specific combination allows to study milling processes comprehensively on the level of the molecular and crystalline structures and thus obtaining reliable data for mechanistic studies. 相似文献
5.
《Angewandte Chemie (International ed. in English)》2017,56(18):4936-4940
Herein, we describe the first catalytic asymmetric intramolecular [4+2] cycloaddition of in situ generated ortho‐quinone methides. In the presence of a confined chiral imidodiphosphoric acid catalyst, various salicylaldehydes react with dienyl alcohols to give transient ortho ‐quinone methide intermediates, which undergo an intramolecular [4+2] cycloaddition to provide highly functionalized furanochromanes and pyranochromanes in excellent diastereoselectivity and enantioselectivity. 相似文献
6.
Youn Jeong Jang Dr. Jae Young Kim Won Yong Kim Prof. Jeong Kon Seo Prof. Sungjee Kim Prof. Kun‐Hong Lee Prof. Jae Sung Lee 《Angewandte Chemie (International ed. in English)》2014,53(23):5852-5857
As a photocathode for CO2 reduction, zinc‐blende zinc telluride (ZnTe) was directly formed on a Zn/ZnO nanowire substrate by a simple dissolution–recrystallization mechanism without any surfactant. With the most negative conduction‐band edge among p‐type semiconductors, this new photocatalyst showed efficient and stable CO formation in photoelectrochemical CO2 reduction at ?0.2–?0.7 V versus RHE without a sacrificial reagent. 相似文献
7.
Xiang Wang Zhen‐Feng Cai Yu‐Qi Wang Ya‐Chen Feng Hui‐Juan Yan Dong Wang Li‐Jun Wan 《Angewandte Chemie (International ed. in English)》2020,59(37):16098-16103
We report a molecular investigation of a cobalt phthalocyanine (CoPc)‐catalyzed CO2 reduction reaction by electrochemical scanning tunneling microscopy (ECSTM). An ordered adlayer of CoPc was prepared on Au(111). Approximately 14 % of the adsorbed species appeared with high contrast in a CO2‐purged electrolyte environment. The ECSTM experiments indicate the proportion of high‐contrast species correlated with the reduction of CoIIPc (?0.2 V vs. saturated calomel electrode (SCE)). The high‐contrast species is ascribed to the CoPc‐CO2 complex, which is further confirmed by theoretical simulation. The sharp contrast change from CoPc‐CO2 to CoPc is revealed by in situ ECSTM characterization of the reaction. Potential step experiments provide dynamic information for the initial stage of the reaction, which include the reduction of CoPc and the binding of CO2, and the latter is the rate‐limiting step. The rate constant of the formation and dissociation of CoPc‐CO2 is estimated on the basis of the in situ ECSTM experiment. 相似文献
8.
A series of Fe?Ni mixed‐oxide catalysts were synthesized by using the sol–gel method for the reduction of NO by CO. These Fe?Ni mixed‐oxide catalysts exhibited tremendously enhanced catalytic performance compared to monometallic catalysts that were prepared by using the same method. The effects of Fe/Ni molar ratio and calcination temperature on the catalytic activity were examined and the physicochemical properties of the catalysts were characterized by using XRD, Raman spectroscopy, N2‐adsorption/‐desorption isotherms, temperature‐programmed reduction with hydrogen (H2‐TPR), temperature‐programmed desorption of nitric oxide (NO‐TPD), and X‐ray photoelectron spectroscopy (XPS). The results indicated that the reduction behavior, surface oxygen species, and surface chemical valence states of iron and nickel in the catalysts were the key factors in the NO elimination. Fe0.5Ni0.5Ox that was calcined at 250 °C exhibited excellent catalytic activity of 100 % NO conversion at 130 °C and a lifetime of more than 40 hours. A plausible mechanism for the reduction of NO by CO over the Fe?Ni mixed‐oxide catalysts is proposed, based on XPS and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analyses. 相似文献
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10.
Catalytic C(sp3)−H Arylation of Free Primary Amines with an exo Directing Group Generated In Situ
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Chengpeng Wang David M. Magness Prof. Guangbin Dong 《Angewandte Chemie (International ed. in English)》2016,55(31):9084-9087
Herein, we report the palladium‐catalyzed direct arylation of unactivated aliphatic C?H bonds in free primary amines. This method takes advantage of an exo‐imine‐type directing group (DG) that can be generated and removed in situ. A range of unprotected aliphatic amines are suitable substrates, undergoing site‐selective arylation at the γ‐position. Methyl as well as cyclic and acyclic methylene groups can be activated. Furthermore, when aniline‐derived substrates were used, preliminary success with δ‐C?H arylation was achieved. The feasibility of using the DG component in a catalytic fashion was also demonstrated. 相似文献
11.
Uncovering the Role of Metal Catalysis in Tetrazole Formation by an In Situ Cycloaddition Reaction: An Experimental Approach
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Dr. Di‐Chang Zhong Ya‐Qiong Wen Ji‐Hua Deng Prof. Dr. Xu‐Zhong Luo Yun‐Nan Gong Prof. Dr. Tong‐Bu Lu 《Angewandte Chemie (International ed. in English)》2015,54(40):11795-11799
Using an experimental approach, the role of metal catalysis has been investigated in the in situ cycloaddition reaction of nitrile with azide to form tetrazoles. It has been shown that metal catalysis serves to activate the cyano group in the nitrile reagent by a coordinative interaction. 相似文献
12.
Probing Interfacial Electronic and Catalytic Properties on Well‐Defined Surfaces by Using In Situ Raman Spectroscopy
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Ya‐Hao Wang Miao‐Miao Liang Yue‐Jiao Zhang Shu Chen Petar Radjenovic Dr. Hua Zhang Prof. Zhi‐Lin Yang Prof. Xiao‐Shun Zhou Prof. Zhong‐Qun Tian Prof. Jian‐Feng Li 《Angewandte Chemie (International ed. in English)》2018,57(35):11257-11261
Heterogeneous metal interfaces play a key role in determining the mechanism and performance of catalysts. However, in situ characterization of such interfaces at the molecular level is challenging. Herein, two model interfaces, Pd and Pt overlayers on Au single crystals, were constructed. The electronic structures of these interfaces as well as effects of crystallographic orientation on them were analyzed by shell‐isolated nanoparticle‐enhanced Raman spectroscopy (SHINERS) using phenyl isocyanide (PIC) as a probe molecule. A clear red shift in the frequency of the C≡N stretch (νNC) was observed, which is consistent with X‐ray photoelectron spectroscopy (XPS) data and indicates that the ultrathin Pt and Pd layers donate their free electrons to the Au substrates. Furthermore, in situ electrochemical SHINERS studies showed that the electronic effects weaken Pt?C/Pd?C bonds, leading to improved surface activity towards CO electrooxidation. 相似文献
13.
Gui‐Rong Zhang Sascha‐Dominic Straub Liu‐Liu Shen Yannick Hermans Patrick Schmatz Andreas M. Reichert Jan P. Hofmann Ioannis Katsounaros Bastian J. M. Etzold 《Angewandte Chemie (International ed. in English)》2020,59(41):18095-18102
The key to fully leveraging the potential of the electrochemical CO2 reduction reaction (CO2RR) to achieve a sustainable solar‐power‐based economy is the development of high‐performance electrocatalysts. The development process relies heavily on trial and error methods due to poor mechanistic understanding of the reaction. Demonstrated here is that ionic liquids (ILs) can be employed as a chemical trapping agent to probe CO2RR mechanistic pathways. This method is implemented by introducing a small amount of an IL ([BMIm][NTf2]) to a copper foam catalyst, on which a wide range of CO2RR products, including formate, CO, alcohols, and hydrocarbons, can be produced. The IL can selectively suppress the formation of ethylene, ethanol and n‐propanol while having little impact on others. Thus, reaction networks leading to various products can be disentangled. The results shed new light on the mechanistic understanding of the CO2RR, and provide guidelines for modulating the CO2RR properties. Chemical trapping using an IL adds to the toolbox to deduce the mechanistic understanding of electrocatalysis and could be applied to other reactions as well. 相似文献
14.
《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2017,129(15):4199-4203
The first asymmetric hydrogenation of in situ generated isochromenylium derivatives is enabled by tandem catalysis with a binary system consisting of Cu(OTf)2 and a chiral cationic ruthenium–diamine complex. A range of chiral 1H ‐isochromenes were obtained in high yields with good to excellent enantioselectivity. These chiral 1H ‐isochromenes could be easily transformed into isochromanes, which represent an important structural motif in natural products and biologically active compounds. The chiral induction was rationalized by density functional theory calculations. 相似文献
15.
Direct Allylation of In Situ Generated Aldehyde Acyl Anions by Synergistic NHC and Palladium Catalysis
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Milind M. Ahire Dr. Santosh B. Mhaske 《Angewandte Chemie (International ed. in English)》2014,53(27):7038-7042
The direct regioselective allylation of in situ generated aldehyde acyl anions has been achieved by synergistic NHC and Pd catalysis. It provides an efficient access to valuable β,γ‐unsaturated ketones under mild reaction conditions starting from easily accessible allylic carbonates and aldehydes without any preactivation. The synergistic catalysis method demonstrated herein adds a new dimension to the area of metal‐mediated C allylation. 相似文献
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17.
In situ Generated Ruthenium Catalyst Systems Bearing Diverse N‐Heterocyclic Carbene Precursors for Atom‐Economic Amide Synthesis from Alcohols and Amines
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Dr. Hua Cheng Mao‐Qian Xiong Chuan‐Xiang Cheng Hua‐Jing Wang Qiang Lu Hong‐Fu Liu Fu‐Bin Yao Dr. Cheng Chen Prof. Dr. Francis Verpoort 《化学:亚洲杂志》2018,13(4):440-448
The transition‐metal‐catalyzed direct synthesis of amides from alcohols and amines is herein demonstrated as a highly environmentally benign and atom‐economic process. Among various catalyst systems, in situ generated N‐heterocyclic carbene (NHC)‐based ruthenium (Ru) halide catalyst systems have been proven to be active for this transformation. However, these existing catalyst systems usually require an additional ligand to achieve satisfactory results. In this work, through extensive screening of a diverse variety of NHC precursors, we discovered an active in situ catalyst system for efficient amide synthesis without any additional ligand. Notably, this catalyst system was found to be insensitive to the electronic effects of the substrates, and various electron‐deficient substrates, which were not highly reactive with our previous catalyst systems, could be employed to afford the corresponding amides efficiently. Furthermore, mechanistic investigations were performed to provide a rationale for the high activity of the optimized catalyst system. NMR‐scale reactions indicated that the rapid formation of a Ru hydride intermediate (signal at δ=?7.8 ppm in the 1H NMR spectrum) after the addition of the alcohol substrate should be pivotal in establishing the high catalyst activity. Besides, HRMS analysis provided possible structures of the in situ generated catalyst system. 相似文献
18.
Phosphorus‐Doped Graphitic Carbon Nitrides Grown In Situ on Carbon‐Fiber Paper: Flexible and Reversible Oxygen Electrodes
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Dr. Tian Yi Ma Jingrun Ran Prof. Sheng Dai Prof. Mietek Jaroniec Prof. Shi Zhang Qiao 《Angewandte Chemie (International ed. in English)》2015,54(15):4646-4650
Flexible non‐metal oxygen electrodes fabricated from phosphorus‐doped graphitic carbon nitride nano‐flowers directly grown on carbon‐fiber paper exhibit high activity and stability in reversibly catalyzing oxygen reduction and evolution reactions, which is a result of N, P dual action, enhanced mass/charge transfer, and high active surface area. The performance is comparable to that of the state‐of‐the‐art transition‐metal, noble‐metal, and non‐metal catalysts. Remarkably, the flexible nature of these oxygen electrodes allows their use in folded and rolled‐up forms, and directly as cathodes in Zn–air batteries, featuring low charge/discharge overpotential and long lifetime. 相似文献
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20.
Hanna H. Cramer Basujit Chatterjee Thomas Weyhermüller Christophe Werl Walter Leitner 《Angewandte Chemie (International ed. in English)》2020,59(36):15674-15681
The catalytic reduction of carbon dioxide (CO2) is considered a major pillar of future sustainable energy systems and chemical industries based on renewable energy and raw materials. Typically, catalysts and catalytic systems are transforming CO2 preferentially or even exclusively to one of the possible reduction levels and are then optimized for this specific product. Here, we report a cobalt‐based catalytic system that enables the adaptive and highly selective transformation of carbon dioxide individually to either the formic acid, the formaldehyde, or the methanol level, demonstrating the possibility of molecular control over the desired product platform. 相似文献