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1.
The amperometric sensor based on a silver nanowire (80 nm in diameter Ag NW) array electrode was fabricated and characterized with scanning electron microscope (SEM). The electrode showed good electrocatalytic activity for reduction of hydrogen peroxide. The effects of the applied polarization potential, pH, time interval between successive injections of analyte, injection volume and H2O2 concentration in a single injection on the electrochemical performance of the sensor were studied. It was found that the optimized operating conditions for the proposed sensor are: the potential of ?200 mV, pH between 7.4 and 9.0, 60 s time interval, 10 µL injection volume, and 500 µM H2O2 in single injection. The proposed Ag NW array sensor is free of interference from ascorbic acid, uric acid and glucose. 相似文献
2.
Structure of Framework Aluminum Lewis Sites and Perturbed Aluminum Atoms in Zeolites as Determined by 27Al{1H} REDOR (3Q) MAS NMR Spectroscopy and DFT/Molecular Mechanics 下载免费PDF全文
Dr. Jiří Brus Libor Kobera Dr. Wolfgang Schoefberger Dr. Martina Urbanová Petr Klein Dr. Petr Sazama Dr. Edyta Tabor Dr. Stepan Sklenak Dr. Anna V. Fishchuk Dr. Jiří Dědeček 《Angewandte Chemie (International ed. in English)》2015,54(2):541-545
Zeolites are highly important heterogeneous catalysts. Besides Brønsted SiOHAl acid sites, also framework AlFR Lewis acid sites are often found in their H‐forms. The formation of AlFR Lewis sites in zeolites is a key issue regarding their selectivity in acid‐catalyzed reactions. The local structures of AlFR Lewis sites in dehydrated zeolites and their precursors—“perturbed” AlFR atoms in hydrated zeolites—were studied by high‐resolution MAS NMR and FTIR spectroscopy and DFT/MM calculations. Perturbed framework Al atoms correspond to (SiO)3AlOH groups and are characterized by a broad 27Al NMR resonance (δi=59–62 ppm, CQ=5 MHz, and η=0.3–0.4) with a shoulder at 40 ppm in the 27Al MAS NMR spectrum. Dehydroxylation of (SiO)3AlOH occurs at mild temperatures and leads to the formation of AlFR Lewis sites tricoordinated to the zeolite framework. Al atoms of these (SiO)3Al Lewis sites exhibit an extremely broad 27Al NMR resonance (δi≈67 ppm, CQ≈20 MHz, and η≈0.1). 相似文献
3.
Trifluoroacetic acid (TFA) is an effective reagent for the demethylation of methyl esters under anhydrous conditions, affording the parent acids and methyl trifluoroacetate. 相似文献
4.
Bartosz Mozgawa Dr. Filip Zasada Dr. Monika Fedyna Prof. Kinga Góra-Marek Dr. Edyta Tabor Dr. Kinga Mlekodaj Dr. Jiří Dědeček Prof. Zhen Zhao Dr. Piotr Pietrzyk Prof. Zbigniew Sojka 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(68):17159-17180
NH3 temperature-programmed desorption (NH3-TPD) is frequently used for probing the nature of the active sites in CuSSZ-13 zeolite for selective catalytic reduction (SCR) of NOx. Herein, we propose an interpretation of NH3-TPD results, which takes into account the temperature-induced dynamics of NH3 interaction with the active centers. It is based on a comprehensive DFT/GGA+D and first-principles thermodynamic (FPT) modeling of NH3 adsorption on single Cu2+, Cu+, [CuOH]+ centers, dimeric [Cu-O-Cu]2+, [Cu-O22−-Cu]2 species, segregated CuO nanocrystals and Brønsted acid sites (BAS). Theoretical TPD profiles are compared with the experimental data measured for samples of various Si/Al ratios and distribution of Al within the zeolite framework. Copper reduction, its relocation, followed by the intrazeolite olation/oxolation processes, which are concomitant with NH3 desorption, were revealed by electron paramagnetic resonance (EPR) and IR. DFT/FPT results show that the peaks in the desorption profiles cannot be assigned univocally to the particular Cu and BAS centers, since the observed low-, medium- and high-temperature desorption bands have contributions coming from several species, which dynamically change their speciation and redox states during NH3-TPD experiment. Thus, a rigorous interpretation of the NH3-TPD profiles of CuSSZ-13 in terms of the strength and concentration of the active centers of a particular type is problematic. Nonetheless, useful connections for molecular interpretation of TPD profiles can be established between the individual component peaks and the corresponding ensembles of the adsorption centers. 相似文献
5.
The study of the analytic structure of nonlinear ordinary and partial differential equations is shown to provide a unified
approach to determining their properties and finding their solutions.
A course of lectures delivered at the School on Chaos and Nonlinear Dynamics held at the Indian Institute of Science, Bangalore,
India (June 24th–July 18th 1987) 相似文献
6.
J. I. Prisciandaro P. F. Mantica B. A. Brown D. W. Anthony M. W. Cooper A. Garcia D. E. Groh A. Komives W. Kumarasiri P. A. Lofy A. M. Oros-Peusquens S. L. Tabor M. Wiedeking 《Physics letters. [Part B]》2001,510(1-4):17-23
An 879.9(2) keV γ-ray transition has been identified following the β decay of 58V and assigned as the 2+1→0+1 transition in 58Cr34. A peak in the energies of the first excited 2+ states for the even–even chromium isotopes is now evident at 56Cr32, providing empirical evidence for a significant subshell gap at N=32. The appearance of this neutron subshell closure for neutron-rich nuclides may be attributed to the diminished π1f7/2–ν1f5/2 monopole proton–neutron interaction as protons are removed from the 1f7/2 single-particle orbital. 相似文献
7.
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9.
We study linear dynamical systems with multidimensional time in Banach spaces. Using Taylor functional calculus we prove that under additional assumptions hyperbolic systems have shadowing property. 相似文献
10.
J. Tabor 《Aequationes Mathematicae》2002,63(1-2):18-25