排序方式: 共有11条查询结果,搜索用时 110 毫秒
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Dr. Chang Hyuck Choi Claudio Baldizzone Jan‐Philipp Grote Dr. Anna K. Schuppert Dr. Frédéric Jaouen Dr. Karl J. J. Mayrhofer 《Angewandte Chemie (International ed. in English)》2015,54(43):12753-12757
Fundamental understanding of non‐precious metal catalysts for the oxygen reduction reaction (ORR) is the nub for the successful replacement of noble Pt in fuel cells and, therefore, of central importance for a technological breakthrough. Herein, the degradation mechanisms of a model high‐performance Fe‐N‐C catalyst have been studied with online inductively coupled plasma mass spectrometry (ICP‐MS) and differential electrochemical mass spectroscopy (DEMS) coupled to a modified scanning flow cell (SFC) system. We demonstrate that Fe leaching from iron particles occurs at low potential (<0.7 V) without a direct adverse effect on the ORR activity, while carbon oxidation occurs at high potential (>0.9 V) with a destruction of active sites such as FeNxCy species. Operando techniques combined with identical location‐scanning transmission electron spectroscopy (IL‐STEM) identify that the latter mechanism leads to a major ORR activity decay, depending on the upper potential limit and electrolyte temperature. Stable operando potential windows and operational strategies are suggested for avoiding degradation of Fe‐N‐C catalysts in acidic medium. 相似文献
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Guoqing Jia Zhaochi Feng Chunying Wei Can Li 《Journal of Raman spectroscopy : JRS》2010,41(12):1615-1620
Human serum albumin (HSA), a model protein, was introduced to the surface‐enhanced Raman spectroscopy (SERS) of cationic porphyrin 5,10,15,20‐tetrakis(1‐methyl‐4‐pyridyl)‐21H,23H‐porphine (H2TMPyP4). HSA was found to have a great influence not only on Ag nanoparticle aggregation state but also on the interaction between Ag nanoparticle and H2TMPyP4 molecules. In the (H2TMPyP4‐Ag colloid)/HSA system, addition of H2TMPyP4 to Ag colloid led to a quick Ag colloid aggregation, and subsequent HSA addition could stabilize this system. The SERS spectrum was dominated by a combination of Ag(II)TMPyP4 and free base H2TMPyP4. More interestingly, a photoinduced demetalation of Ag(II)TMPyP4 to free base H2TMPyP4 was observed in the (H2TMPyP4‐Ag colloid)/HSA system. This demetalation process was partially reversible when the laser was turned off or the laser power was reduced. In this case, HSA acts as both a stabilizer and a demetalation promoter. In the (HSA‐H2TMPyP4)/Ag colloid system, when H2TMPyP4 was premixed with HSA prior to the Ag colloid addition, no obvious Ag colloid aggregation appeared, and the SERS spectrum was just characteristic of free base H2TMPyP4. In this case, HSA is proposed to function as both a stabilizer and a molecular spacer. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
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A ruthenium-mediated dearomatization sequence has been developed that delivers structurally intriguing azaspirolactam products in stereoselective fashion. Treatment of (η6-arene)Ru(cyclopentadienyl) complexes bearing N-benzyl-β-amido phosphonate side chains with excess NaH results in intramolecular nucleophilic aromatic addition to the ipso position of the coordinated arenes. Subsequent Horner–Wadsworth–Emmons (HWE) reaction with added aldehydes affords olefinated spirolactam cyclohexadienyl ruthenium complexes. Mild oxidation with CuCl2 or CuBr2 under CO effects removal and recovery of the CpRu(II) fragment. Substituents present on the cyclohexadienyl skeleton influence the outcome of demetalation and products obtained in this study include functionalized 2-azaspiro[4.5]decanes and tetrahydroisoquinolinones. 相似文献
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Umpolung of Methylenephosphonium Ions in Their Manganese Half‐Sandwich Complexes and Application to the Synthesis of Chiral Phosphorus‐Containing Ligand Scaffolds 下载免费PDF全文
Dr. Dmitry A. Valyaev Dr. Oleg A. Filippov Dr. Noël Lugan Dr. Guy Lavigne Prof. Dr. Nikolai A. Ustynyuk 《Angewandte Chemie (International ed. in English)》2015,54(21):6315-6319
Half‐sandwich manganese methylenephosphonium complexes [Cp(CO)2Mn(η2‐R2P?C(H)Ph)]BF4 were obtained in high yield through a straightforward reaction sequence involving a classical Fischer‐type manganese complex and a secondary phosphine as key starting materials. The addition of various nucleophiles (Nu) to these species took place regioselectively at the double‐bonded carbon center of the coordinated methylenephosphonium ligand R2P+?C(H)Ph to produce the corresponding chiral phosphine complexes [Cp(CO)2Mn(κ1‐R2P? C(H)(Ph)Nu)], from which the phosphines were ultimately recovered as free entities upon simple irradiation with visible light. The synthetic potential of this umpolung approach is illustrated herein by the preparation of novel chiral pincer‐type phosphine–NHC–phosphine ligand architectures. 相似文献
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Łukasz Orzeł Mateusz Świrski Grażyna Stochel 《Journal of Coordination Chemistry》2018,71(11-13):1837-1851
AbstractMagnesium complexes with reduced tetrapyrrolic ligands are active compounds of plant and bacteria photosystems. However, also the porphyrin complex appears as an intermediate on the biosynthetic pathway of the photosynthetic pigments. Its transformations, in particular the reduction of pyrrole rings, lead to the acquisition of the properties that are primary for activity in antenna systems and reaction centers. On the other hand, modifications of the porphyrin system must affect the resistance to destructive processes, such as loss of metal ion and its substitution. In order to compare the stability of three natural Mg complexes, namely Mg protoporphyrin IX, chlorophyll a, and bacteriochlorophyll a, spectroscopic studies in solution were performed. The difference in the electronic structure of the macrocyclic ligand was the basic variable in testing the action against d-electron metal salts and acetic acid. The spectroscopic studies were supplemented with calculations using the Density Functional Theory which provided insight into the stability of M(II)-N bonds depending on the dimension of the delocalized electron system. The results indicate the decreasing stability of Mg(II) complexes on the biosynthetic pathway, thereby providing an additional justification for incorporation of the metal ion into porphyrin prior to the electronic modifications of the tetrapyrrolic system. 相似文献
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