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131.
Tim Mller Fabian Scholten Trung Ngo Thanh Ilya Sinev Janis Timoshenko Xingli Wang Zarko Jovanov Manuel Gliech Beatriz Roldan Cuenya Ana Sofia Varela Peter Strasser 《Angewandte Chemie (International ed. in English)》2020,59(41):17974-17983
The direct electrochemical conversion of carbon dioxide (CO2) into multi‐carbon (C2+) products still faces fundamental and technological challenges. While facet‐controlled and oxide‐derived Cu materials have been touted as promising catalysts, their stability has remained problematic and poorly understood. Herein we uncover changes in the chemical and morphological state of supported and unsupported Cu2O nanocubes during operation in low‐current H‐Cells and in high‐current gas diffusion electrodes (GDEs) using neutral pH buffer conditions. While unsupported nanocubes achieved a sustained C2+ Faradaic efficiency of around 60 % for 40 h, the dispersion on a carbon support sharply shifted the selectivity pattern towards C1 products. Operando XAS and time‐resolved electron microscopy revealed the degradation of the cubic shape and, in the presence of a carbon support, the formation of small Cu‐seeds during the surprisingly slow reduction of bulk Cu2O. The initially (100)‐rich facet structure has presumably no controlling role on the catalytic selectivity, whereas the oxide‐derived generation of under‐coordinated lattice defects, can support the high C2+ product yields. 相似文献
132.
Janis V. Musso Mathis J. Benedikter Dr. Dongren Wang Dr. Wolfgang Frey Hagen J. Altmann Prof. Dr. Michael R. Buchmeiser 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(40):8709-8713
The first reversible N-heterocyclic carbene (NHC) induced α-H abstraction in tungsten(VI) imido-dialkyl dialkoxide complexes is reported. Treatment of W(NAr)(CH2Ph)2(OtBu)2 (Ar=2,6-dichlorophenyl, 2,6-dimethylphenyl, 2,6-diisopropylphenyl) with different NHCs leads to the formation of complexes of the type W(NAr)(CHPh)(NHC)(CH2Ph)(OtBu) in excellent isolated yields of up to 96 %. The highly unusual release of the tert-butoxide ligand as tBuOH in the course of the reaction was observed. The formed alkylidene complexes and tBuOH are in an equilibrium with the NHC and the dialkyl complexes. Reaction kinetics were monitored by 1H NMR spectroscopy. A correlation between the steric and electronic properties of the NHC and the reaction rates was observed. Kinetics of a deuterium-labeled complex in comparison to its non-deuterated counterpart revealed the presence of a strong primary kinetic isotope effect (KIE) of 4.2, indicating that α-H abstraction is the rate-determining step (RDS) of the reaction. 相似文献
133.
Axel Munk Jean-Pierre Stockis Janis Valeinis G?tz Giese 《Annals of the Institute of Statistical Mathematics》2011,63(5):939-959
We establish a data-driven version of Neyman??s smooth goodness-of-fit test for the marginal distribution of observations generated by an ??-mixing discrete time stochastic process ${(X_t)_{t \in \mathbb {Z}}}$ . This is a simple extension of the test for independent data introduced by Ledwina (J Am Stat Assoc 89:1000?C1005, 1994). Our method only requires additional estimation of the cumulative autocovariance. Consistency of the test will be shown at essentially any alternative. A brief simulation study shows that the test performs reasonable especially for the case of positive dependence. Finally, we illustrate our approach by analyzing the validity of a forecasting method (??historical simulation??) for the implied volatilities of traded options. 相似文献
134.
A convenient method for preparing substituted anilines via a Rh-catalyzed [2 + 2 + 2] cycloaddition reaction of diynes and 2-oxazolone was discovered. The initial cycloaddition adducts undergo facile decarboxylation of carbon dioxide to afford aniline products. Reaction conditions are mild, and only 3 mol % Rh catalyst is required. High regioselectivity was observed when an unsymmetrical diyne was used as a starting material. 相似文献
135.
Tatjana Ivanova Tatjana Bocoka Janis Zicans Valdis Kalkis Martins Kalnins 《Macromolecular Symposia》2001,170(1):105-114
The results are given on the effect of γ‐irradiation on properties of blends of high and low‐density polyethylene (HDPE, LDPE) with elastomers ‐ethylene/propylene/diene rubber (EPDM) and chlorinated polyethylene (CPE), and thermotropic liquid crystalline polymer (LCP). The morphological, thermal, mechanical properties (including thermosetting properties) and adhesion properties of blended composites were investigated. A special attention was paid to the applicability of the blends as thermosetting materials (TSM). The LCP used was a copolyester of poly(ethylene terephthalate) with p‐(hydroxybenzoic acid) in the ratio 40 : 60. It was found that addition of LCP essentially influenced the thermomechanical and adhesion properties of PE composites, irradiated up to the absorbed dose 150 kGy, as well as the dimensional stability of thermosetting products, made from polyethylene/elastomer mixtures. The results show that such ternary blends considerably improve the exploitation conditions of irradiated polyethylene and useful thermosetting materials can be obtained. 相似文献
136.
Janis Priede 《Studies in Applied Mathematics》2023,150(2):457-480
We show that interfacial gravity waves comprising strong hydraulic jumps (bores) can be described by a two-layer hydrostatic shallow-water (SW) approximation without invoking additional front conditions. The theory is based on a new SW momentum equation which is derived in locally conservative form containing a free parameter α. This parameter, which defines the relative contribution of each layer to the pressure at the interface, affects only hydraulic jumps but not continuous waves. The Rankine–Hugoniot jump conditions for the momentum and mass conservation equations are found to be mathematically equivalent to the classical front conditions, which were previously thought to be outside the scope of SW approximation. Dimensional arguments suggest that α depends on the density ratio. For nearly equal densities, both layers are expected to affect interfacial pressure with approximately equal weight coefficients, which corresponds to . The front propagation velocity for agrees well with experimental and numerical results in a wide range of bore strengths. A remarkably better agreement with high-accuracy numerical results is achieved by , which yields the largest height that a stable gravity current can have. 相似文献