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排序方式: 共有315条查询结果,搜索用时 78 毫秒
91.
MohammadReza Elahifard Elham Fazeli Azadeh Joshani MohammadReza Gholami 《Surface and interface analysis : SIA》2013,45(7):1081-1087
Direct CO dissociation is seen the main path of the first step in the Fischer–Tropsch Synthesis (FTS) on the reactive iron surfaces. Cu/Fe alloy film is addressed with various applications over face‐centered‐cubic (fcc)‐Cu and body‐centered‐cubic (bcc)‐Fe in the FTS, i.e. preventing iron carbide formation (through direct CO dissociation) by moderating the surface reactivity and facilitating the reduction of iron surfaces, respectively. In this study by density functional theory, the stable configurations of CO molecule on various Cu/Fe alloys over fcc‐Cu(100) and bcc‐Fe(100) surfaces with different CO coverage (25% and 50%) have been evaluated. Our results showed that the ensemble effect plays a fundamental role to CO adsorption energy on the surface alloys over bcc‐Fe(100); on the other hand, the ligand effect determines the CO stability on the fcc‐Cu(100) surface alloys. CO dissociation barrier was also calculated on the surface alloys that showed although the CO dissociation process is thermodynamically possible on the more reactive surface alloys, but according to their high barrier, CO dissociation does not occur directly on these surfaces. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
92.
A simple protocol was established to synthesize 2,3-dialkyl indoles and various tetrahydrocarbazoles via Fischer indole synthesis. This method uses ceric ammonium nitrate as a catalyst for the Fischer indole synthesis with substituted phenyl hydrazine hydrochlorides and 2-butanone, phenyl propanal, and cyclohexanone. This process is a practical synthetic method for the preparation of various 2,3-disubstituted alkyl indoles and tetrahydrocarbazoles. 相似文献
93.
Melanie B. Freitas Kelly A. SimollardesCaroline M. Rufo Chantel N. McLellanGabrielle J. Dugas Leslie E. LupienElizabeth A. Colby Davie 《Tetrahedron letters》2013
Reported herein is a bidirectional synthesis of symmetric N,N′-diacyl hydrazide compounds closely resembling the alkaloid natural product montamine. In the process, di-tert-butyl hydrazine-1,2-dicarboxylate was smoothly dialkylated with alkyl halides, then Boc deprotected and acylated with an acetate-protected acid chloride derived from ferulic acid. After acetate removal, simple montamine analogs were obtained in excellent overall yields. Fischer indole synthesis with 4-methoxyphenylhydrazine hydrochloride and dihydrofuran provided 5-methoxytryptophol, which was then elaborated to the 1,2-bis(5-methoxyindol-3-yl)hydrazide structure bearing the substitution pattern found in montamine. 相似文献
94.
Dr. Huan Wang Dr. Alexander V. Predeus Prof. William D. Wulff 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(25):8261-8267
The double benzannulation of bis‐carbene complexes of chromium with α,ω‐diynes generates [m.n]cyclophanes in which all three rings are generated in a single reaction. This triple annulation process is very flexible allowing for the construction of symmetrical [n.n]cyclophanes and unsymmetrical [m.n]cyclophanes as well as isomers in which the two benzene rings are both meta bridged or both para bridged, and isomers that contain both meta and para bridges. The connectivity patterns of the bridges in the cyclophanes can be controlled by regioselectivity transfer from the bis‐vinyl carbene complexes in which the substitution pattern of the vinyl groups in the carbene complexes dictate the connectivity pattern in the [m.n]cyclophanes. This synthesis of [n.n]cyclophanes is quite flexible with regard to ring size and can be used with tether lengths ranging from n=2 to n=16 and thus to ring sizes with up to 40 member rings. The only limitation to regioselectivity transfer from the carbene complexes to the [m.n]cyclophanes was found in the synthesis of para,para‐cyclophanes with four carbon tethers for which the loss of fidelity occurred with the unexpected formation of meta,para‐cyclophanes. 相似文献
95.
Size‐Dependent Phase Transformation of Catalytically Active Nanoparticles Captured In Situ 下载免费PDF全文
Dr. Nico Fischer Brett Clapham Dr. Theresa Feltes Prof. Dr. Eric van Steen Prof. Dr. Michael Claeys 《Angewandte Chemie (International ed. in English)》2014,53(5):1342-1345
The utilization of metal nanoparticles traverses across disciplines and we continue to explore the intrinsic size‐dependent properties that make them so unique. Ideal nanoparticle formulation to improve a process’s efficiency is classically presented as exposing a greater surface area to volume ratio through decreasing the nanoparticle size. Although, the physiochemical characteristics of the nanoparticles, such as phase, structure, or behavior, may be influenced by the nature of the environment in which the nanoparticles are subjected 1 , 2 and, in some cases, could potentially lead to unwanted side effects. The degree of this influence on the particle properties can be size‐dependent, which is seldom highlighted in research. Herein we reveal such an effect in an industrially valuable cobalt Fischer–Tropsch synthesis (FTS) catalyst using novel in situ characterization. We expose a direct correlation that exists between the cobalt nanoparticle’s size and a phase transformation, which ultimately leads to catalyst deactivation. 相似文献
96.
(Iodizing side reaction in Karl Fischer reactions.) Imidazole is iodized to mono- and diiodoimidazole under conditions normally used in the Karl Fischer reaction. This side reaction is greatly accelerated by the polarizing effect of formamide on I2. The dependence of the reaction rate constant on the amount of formamide in methanolic KF solutions has been determined by photometry. During the titration a blank consumption of I2 occurs and some types of automatic KF titrators may be unable to detect an endpoint. However, bipotentiometric titration in pure formamide is principally possible; the necessary precautions are pointed out. The known increase of the reaction rate in purely methanolic KF solutions at pH > 8 is also shown to be caused by the iodizing side reaction. 相似文献
97.
Marchetti S. G. Cagnoli M. V. Alvarez A. M. Bengoa J. F. Gallegos N. G. Yeramián A. A. Mercader R. C. 《Hyperfine Interactions》2002,139(1-4):33-40
We have synthesized mesoporous MCM-41 and have used it as a support for iron particles to be employed as a catalyst in the Fischer–Tropsch reaction. The solids were characterized by Mössbauer spectroscopy, X-ray diffraction, BET, TGA, CO chemisorption and volumetric oxidation. Although the catalyst showed a high CO conversion when it was used in the hydrocarbon synthesis from CO and H2 (14.3% at 1 h of reaction time) mainly methane was formed. The high methane production is likely related to the very small size of the metal particles obtained. We suggest some ways to improve the selectivity. 相似文献
98.
Guoyan Zhao Chenghua Zhang Shaodong Qin Hongwei Xiang Yongwang Li 《Journal of molecular catalysis. A, Chemical》2008,286(1-2):137-142
The Fischer–Tropsch synthesis (FTS) performances of iron-based catalysts promoted with/without potassium compounds containing different acidic structural promoters (Al2O3, SiO2, and ZSM-5) were studied in this research. Characterization technologies of temperature-programmed reduction with CO (CO-TPR), powder X-ray diffraction (XRD) and Mössbauer effect spectroscopy (MES) were used to study the effect of K–structural promoter interactions on the carburization behaviors of catalysts. It showed that the addition states of potassium (K–Al2O3, K–SiO2, K–ZSM-5 and K-free) have a significant influence on the formation of iron carbides, which shows a following sequence in promotion of carburization: K–Al2O3 > K–SiO2 > K–ZSM-5 > K-free. The FTS reaction test was performed in a fixed bed reactor. It is found that Fe/K–Al2O3 catalyst leads to the highest CO conversion, Fe/K–ZSM-5 catalyst shows the highest H2 conversion, and Fe/K-free catalyst shows the lowest CO and H2 conversion. As for the hydrocarbon selectivity, Fe/K–SiO2 catalyst yields the lowest methane and the highest C5+ products, Fe/K–ZSM-5 catalyst yields higher methane and the highest liquid hydrocarbon product, whereas Fe/K-free catalyst yields the highest methane and the lowest C5+ products. These results can be explained from the interaction between potassium and structure promoters, and the spillover of reactants or intermediates from Fe sites to the surfaces of structural promoters. 相似文献
99.
100.
Dr. Zhiyu Zou Dr. Alessandro Sala Dr. Mirco Panighel Dr. Ezequiel Tosi Dr. Paolo Lacovig Dr. Silvano Lizzit Dr. Mattia Scardamaglia Dr. Esko Kokkonen Dr. Cinzia Cepek Dr. Cristina Africh Prof. Giovanni Comelli Prof. Dr. Sebastian Günther Prof. Dr. Laerte L. Patera 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2023,135(1):e202213295
The synthesis of high-value fuels and plastics starting from small hydrocarbon molecules plays a central role in the current transition towards renewable energy. However, the detailed mechanisms driving the growth of hydrocarbon chains remain to a large extent unknown. Here we investigated the formation of hydrocarbon chains resulting from acetylene polymerization on a Ni(111) model catalyst surface. Exploiting X-ray photoelectron spectroscopy up to near-ambient pressures, the intermediate species and reaction products have been identified. Complementary in situ scanning tunneling microscopy observations shed light onto the C−C coupling mechanism. While the step edges of the metal catalyst are commonly assumed to be the active sites for the C−C coupling, we showed that the polymerization occurs instead on the flat terraces of the metallic surface. 相似文献