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排序方式: 共有119条查询结果,搜索用时 15 毫秒
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V. I. Zaikovskii A. V. Vosmerikov V. F. Anufrienko L. L. Korobitsyna E. G. Kodenev G. V. Echevskii N. T. Vasenin S. P. Zhuravkov E. V. Matus Z. R. Ismagilov V. N. Parmon 《Kinetics and Catalysis》2006,47(3):389-394
The MoZSM-5 (4.0 wt % Mo) catalyst has been characterized by high-resolution transmission electron microscopy, EDXA, and EPR. Two types of molybdenum-containing particles are stabilized in the catalyst in the course of nonoxidative methane conversion at 750°C. These are 2-to 10-nm molybdenum carbide particles on the zeolite surface and clusters smaller than 1 nm in zeolite channels. According to EPR data, these clusters contain the oxidized molybdenum form Mo5+. The surface Mo2C particles are deactivated at the early stages of the reaction because of graphite condensation on their surface. Methane is mainly activated on oxidized molybdenum clusters located in the open molecular pores of the zeolite. The catalyst is deactivated after the 420-min-long operation because of coke buildup on the zeolite surface and in the zeolite pores. 相似文献
3.
Pter Molnr Jzsef Deli Zoltn Matus Gyula Tth Andrea Steck Hanspeter Pfander 《Helvetica chimica acta》1997,80(1):221-229
β-Cryptoxanthin ( 1 ) was acetylated and then epoxidized with monoperoxyphthalic acid. After hydrolysis, repeated chromatography, and crystallization, (3S,5R,6S)-5,6-epoxy-β-cryptoxanthin ( 3 ), (3S,5S,6R)-5,6-epoxy-β-cryptoxanthin ( 4 ), (3R,5′R,6′R)-5′,6′-epoxy-β-cryptoxanthin ( 5 ), (3S,5R,6S,5′R,6′S)-5,6:5′,6′-diepoxy-β-cryp-toxanthin ( 6 ), and (3S,5S,6R,5′S,6′R)-5,6:5′,6′-diepoxy-β-cryptoxanthin ( 7 ) were isolated as main products and characterized by their UV/VIS, CD, 1H- and 13C-NMR, and mass spectra. The comparison of the carotenoid isolated from yellow, tomato-shaped paprika (Capsicum annuum var. lycopersiciforme flavum) with 3–5 strongly supports the structure of 3 for the natural product. 相似文献
4.
Summary Reinvestigation by HPLC of the petals ofLilium tigrinum and the isolation of some minor compounds is reported. Using HPLC-controlled, preparative-column chromatography, 5,6-diakarpoxanthin
(6), 6-epikarpoxanthin (2), 5,6-diacapsokarpoxanthin (8), and 9Z-antheraxanthin (9Z-13) were isolated and characterized. Based on spectroscopic data the absolute configurations of6 and8 were identical with those originating from paprika, thus the 5,6-diakarpoxanthin (6) and 5,6-diacapsokarpoxanthin (8) have the 3S, 5S, 6S configuration and 6-epikarpoxanthin (2) has the 3S, 5R, 6S configuration.
Presented at: Balaton Symposium on High-Performance Separation Methods, Siófok, Hungary, September 3–5, 1997. 相似文献
5.
L. B. Okhlopkova E. V. Matus I. Z. Ismagilov M. A. Kerzhentsev I. P. Prosvirin Z. R. Ismagilov 《Journal of Structural Chemistry》2013,54(6):1034-1043
A new method is developed to obtain nanosized catalytic Pt-Sn/TiO2 coatings on the inner surface of a capillary microreactor during adsorption of polynuclear carbonyl Pt-Sn complexes on mesoporous TiO2. Titanium oxide sol prepared in the presence of template (Pluronic F127 surfactant) is supported in dynamic mode. Pt-Sn bimetallic catalysts with an average particle size of 1.5–2 nm are synthesized by adsorption of the bimetallic [Pt3(CO)3(SnCl3)2(SnCl2·H2O)] n 2n? complex followed by thermal treatment. Physicochemical properties of samples (thickness, structure and morphology, chemical composition of the material, electronic state, specific surface area, pore volume and size distribution) are characterized by a set of methods (HR TEM, SEM, powder XRD, XRF, XPS, low-temperature nitrogen adsorption). Conditions to prepare the uniform non-peelable Pt-Sn/TiO2 coating on the inner surface of a silica capillary with good adhesion are determined. To increase the TiO2 thickness, multilayered TiO2 films are synthesized by layerby layer deposition. The coating thickness is found to increase with an increase in the capillary diameter. The coating of a capillary with a diameter of 0.55 mm after 14-fold deposition is characterized by a thickness of 2 μm and an average pore size of 5.4 nm. The solvent effect on the adsorption of Pt-Sn carbonyl complexes into the TiO2 support is studied. The amount of the adsorbed complex increases in the following order: ethanol < acetone ~ tetrahydrofuran. The physicochemical properties of the active component (surface concentration, dispersion, and composition) can be fine-tuned by varying the deposition method, precursor concentration in the initial solution, and temperature conditions of activation treatment. The catalyst activity in citral hydrogenation was 0.06–0.54 min?1, with the selectivity with respect to unsaturated alcohols reaching 90% at citral conversion above 95%. 相似文献
6.
Veronika Petrulova Maria Vilkova Zuzana Kovalikova Matus Sajko Miroslav Repcak 《Molecules (Basel, Switzerland)》2020,25(23)
Phytochemical investigations of Matricaria chamomilla L. (Asteraceae) stated the presence of several compounds with an established therapeutic and antioxidant potential. The chamomile non-enzymatic antioxidant system includes low molecular mass compounds, mainly polyphenols such as cinnamic, hydroxybenzoic and chlorogenic acids, flavonoids and coumarins. The objective of this work was to evaluate the role of the non-enzymatic antioxidant system after stimulation by ethylene in tetraploid chamomile plants. Seven days of ethylene treatment significantly increased the activity of phenylalanine ammonia-lyase, which influenced the biosynthesis of protective polyphenols in the first step of their biosynthetic pathway. Subsequently, considerable enhanced levels of phenolic metabolites with a substantial antioxidant effect (syringic, vanillic and caffeic acid, 1,5-dicaffeoylquinic acid, quercetin, luteolin, daphnin, and herniarin) were determined by HPLC-DAD-MS. The minimal information on the chlorogenic acids function in chamomile led to the isolation and identification of 5-O-feruloylquinic acid. It is accumulated during normal conditions, but after the excessive effect of abiotic stress, its level significantly decreases and levels of other caffeoylquinic acids enhance. Our results suggest that ethephon may act as a stimulant of the production of pharmaceutically important non-enzymatic antioxidants in chamomile leaves and thus, lead to an overall change in phytochemical content and therapeutic effects of chamomile plants, as well. 相似文献
7.
G. L. Marcinkiewicz P. P. Matus M. M. Chuiko 《Computational Mathematics and Mathematical Physics》2010,50(6):1024-1037
The monotonicity and stability of a finite difference scheme with respect to initial data in the supremum norm are analyzed
as applied to the polytropic gas equations written in terms of Rie-mann invariants for subsonic flows with 1 < γ < 3. Conditions
on the initial and boundary data are obtained under which subsonic flows with no shock waves develop in the medium. The theoretical
conclusions are supported by numerical results. 相似文献
8.
9.
A new model for high-energy ion implantation is proposed, based on the use of the Fokker-Planck equation. An efficient algorithm
of the adaptive type is devised for the numerical solution of the problem. A simulation of the implantation of boron in silicon
is carried out for energies ranging from 10 to 100 MeV. Good agreement is obtained with the experimental data and the results
of Monte Carlo simulations.
Zh. Tekh. Fiz. 67, 61–67 (January 1997) 相似文献
10.
New second-order accurate monotone difference schemes on nonuniform spatial grids for two-dimensional stationary and nonstationary convection–diffusion equations are proposed. The monotonicity and stability of the solutions of the computational methods with respect to the boundary conditions, the initial condition, and the right-hand side are proved. Two-sided and corresponding a priori estimates are obtained in the grid norm of C. The convergence of the proposed algorithms to the solution of the original differential problem with the second order is proved. 相似文献