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991.
采用等体积共浸渍法,制备了一批不同钾含量的KxMo P/Al2O3(x表示K与Mo摩尔比,0≤x≤3)催化剂,考察其对高硫合成气制甲硫醇性能的影响,并采用X射线衍射分析(XRD)、程序升温还原法(TPR)和激光拉曼光谱(LRS)等技术手段对催化剂进行了表征。结果表明,氧化铝负载的磷钼氧化物前驱体在850℃经H2气还原制备出了Mo P/Al2O3催化剂,少量添加钾催化剂有较高的甲烷选择性,大量添加钾助剂促进了催化剂表面活泼钼硫物种的生成,使得磷化钼基催化剂有较好的甲硫醇选择性,而过量添加钾又会阻碍了甲硫醇的生成。当n(K)/n(Mo)比在2~2.5之间时,磷化钼基催化剂对该反应有较好的催化活性。 相似文献
992.
A Cu(OTf)2-catalyzed simple synthetic approach for highly substituted 1-alkoxy imidazole has been described. This protocol involves (3 + 2) cycloaddition of oximino carbenoids with organo nitriles. This method has wide substrate scope and tolerates alkyl, aryl, substituted aryl, vinyl, and ester nitriles. 相似文献
993.
Molybdenum Speciation and its Impact on Catalytic Activity during Methane Dehydroaromatization in Zeolite ZSM‐5 as Revealed by Operando X‐Ray Methods 下载免费PDF全文
Dr. Inés Lezcano‐González Ramon Oord Dr. Mauro Rovezzi Dr. Pieter Glatzel Prof. Dr. Stanley W. Botchway Prof. Dr. Bert M. Weckhuysen Prof. Dr. Andrew M. Beale 《Angewandte Chemie (International ed. in English)》2016,55(17):5215-5219
Combined high‐resolution fluorescence detection X‐ray absorption near‐edge spectroscopy, X‐ray diffraction, and X‐ray emission spectroscopy have been employed under operando conditions to obtain detailed new insight into the nature of the Mo species on zeolite ZSM‐5 during methane dehydroaromatization. The results show that isolated Mo–oxo species present after calcination are converted by CH4 into metastable MoCxOy species, which are primarily responsible for C2Hx/C3Hx formation. Further carburization leads to MoC3 clusters, whose presence coincides with benzene formation. Both sintering of MoC3 and accumulation of large hydrocarbons on the external surface, evidenced by fluorescence‐lifetime imaging microscopy, are principally responsible for the decrease in catalytic performance. These results show the importance of controlling Mo speciation to achieve the desired product formation, which has important implications for realizing the impact of CH4 as a source for platform chemicals. 相似文献
994.
Dual‐Doped Molybdenum Trioxide Nanowires: A Bifunctional Anode for Fiber‐Shaped Asymmetric Supercapacitors and Microbial Fuel Cells 下载免费PDF全文
Minghao Yu Xinyu Cheng Yinxiang Zeng Zilong Wang Prof. Yexiang Tong Prof. Xihong Lu Prof. Shihe Yang 《Angewandte Chemie (International ed. in English)》2016,55(23):6762-6766
A novel in situ N and low‐valence‐state Mo dual doping strategy was employed to significantly improve the conductivity, active‐site accessibility, and electrochemical stability of MoO3, drastically boosting its electrochemical properties. Consequently, our optimized N‐MoO3?x nanowires exhibited exceptional performances as a bifunctional anode material for both fiber‐shaped asymmetric supercapacitors (ASCs) and microbial fuel cells (MFCs). The flexible fiber‐shaped ASC and MFC device based on the N‐MoO3?x anode could deliver an unprecedentedly high energy density of 2.29 mWh cm?3 and a remarkable power density of 0.76 μW cm?1, respectively. Such a bifunctional fiber‐shaped N‐MoO3?x electrode opens the way to integrate the electricity generation and storage for self‐powered sources. 相似文献
995.
Engineering Chemically Exfoliated Large‐Area Two‐Dimensional MoS2 Nanolayers with Porphyrins for Improved Light Harvesting 下载免费PDF全文
Hanyu Zhang Prof. Jungwook Choi Arjun Ramani Dr. Damien Voiry Sean N. Natoli Prof. Manish Chhowalla Prof. David R. McMillin Prof. Jong Hyun Choi 《Chemphyschem》2016,17(18):2854-2862
Molybdenum disulfide (MoS2) is a promising candidate for electronic and optoelectronic applications. However, its application in light harvesting has been limited in part due to crystal defects, often related to small crystallite sizes, which diminish charge separation and transfer. Here we demonstrate a surface‐engineering strategy for 2D MoS2 to improve its photoelectrochemical properties. Chemically exfoliated large‐area MoS2 thin films were interfaced with eight molecules from three porphyrin families: zinc(II)‐, gallium(III)‐, iron(III)‐centered, and metal‐free protoporphyrin IX (ZnPP, GaPP, FePP, H2PP); metal‐free and zinc(II) tetra‐(N‐methyl‐4‐pyridyl)porphyrin (H2T4, ZnT4); and metal‐free and zinc(II) tetraphenylporphyrin (H2TPP, ZnTPP). We found that the photocurrents from MoS2 films under visible‐light illumination are strongly dependent on the interfacial molecules and that the photocurrent enhancement is closely correlated with the highest occupied molecular orbital (HOMO) levels of the porphyrins, which suppress the recombination of electron–hole pairs in the photoexcited MoS2 films. A maximum tenfold increase was observed for MoS2 functionalized with ZnPP compared with pristine MoS2 films, whereas ZnT4‐functionalized MoS2 demonstrated small increases in photocurrent. The application of bias voltage on MoS2 films can further promote photocurrent enhancements and control current directions. Our results suggest a facile route to render 2D MoS2 films useful for potential high‐performance light‐harvesting applications. 相似文献
996.
Salicylhydroxamic acid (H3shi) is known for its strong coordination ability and multiple coordination modes, and can easily coordinate to metal cations to form compounds with five‐ or six‐membered rings, as well as mono‐, di‐ and multinuclear compounds with interesting structures having potential applications in organic chemistry, coordination chemistry, and the materials and biological sciences. A novel octanuclear nickel(II)–molybdenum(VI) heterometallic cluster based on the salicylhydroxamate ligand, namely di‐μ3‐acetato‐di‐μ2‐acetato‐di‐μ3‐hydroxido‐di‐μ3‐oxido‐tetraoxidooctakis(pyridine‐κN)bis(μ5‐salicylhydroxamato)hexanickel(II)dimolybdenum(VI) monohydrate, [Mo2Ni6(C7H4NO3)2(C2H3O2)4O5(OH)2(C5H5N)8]·H2O, (I), was synthesized by the reaction of sodium molybdate, nickel acetate and salicylhydroxamic acid in a dimethylformamide/pyridine/methanol solution at room temperature. The salicylhydroxamate(3−) (shi3−), acetate and oxide ligands adopt complicated coordination modes and link six NiII and two MoVI cations into the octanuclear heterometallic cluster. All of the metal cations exhibit octahedral coordination geometries and are connected to each other through the sharing of corners, edges or planes. The heterometallic clusters are further connected to form two‐dimensional supramolecular layers through weak C—H…O hydrogen bonds. Studies of the magnetic properties of the title compound reveal antiferromagnetic interactions between the NiII cations. 相似文献
997.
A Facile Strategy for the Preparation of MoS3 and its Application as a Negative Electrode for Supercapacitors 下载免费PDF全文
Tong Zhang Prof. Ling‐Bin Kong Yan‐Hua Dai Kun Yan Ming Shi Prof. Mao‐Cheng Liu Prof. Yong‐Chun Luo Prof. Long Kang 《化学:亚洲杂志》2016,11(17):2392-2398
Owing to their graphene‐like structure and available oxidation valence states, transition metal sulfides are promising candidates for supercapacitors. Herein, we report the application of MoS3 as a new negative electrode for supercapacitors. MoS3 was fabricated by the facile thermal decomposition of a (NH4)2MoS4 precursor. For comparison, samples of MoS3&MoS2 and MoS2 were also synthesized by using the same method. Moreover, this is the first report of the application of MoS3 as a negative electrode for supercapacitors. MoS3 displayed a high specific capacitance of 455.6 F g?1 at a current density of 0.5 A g?1. The capacitance retention of the MoS3 electrode was 92 % after 1500 cycles, and even 71 % after 5000 cycles. In addition, an asymmetric supercapacitor assembly of MoS3 as the negative electrode demonstrated a high energy density at a high potential of 2.0 V in aqueous electrolyte. These notable results show that MoS3 has significant potential in energy‐storage devices. 相似文献
998.
Vibrational and Structural Dynamics of Mn(CO)5Br and Re(CO)5Br Examined Using Nonlinear Infrared Spectroscopy 下载免费PDF全文
Vibrational and structural dynamics of two transition metal carbonyl complexes, Mn(CO)5Br and Re(CO)5Br were examined in DMSO, using ultrafast infrared pump-probe spectroscopy, steady-state linear infrared spectroscopy and quantum chemistry computations. Two carbonyl stretching vibrational modes (a low-frequency A1 mode and two high-frequency degenerate E modes) were used as vibrational probes. Central metal effect on the CO bond order and force constant was responsible for a larger E-A1 frequency separation and a generally more red-shifted E and A1 peaks in the Re complex than in the Mn complex. A generally broader spectral width for the A1 mode than the E mode is believed to be partially due to vibrational lifetime effect. Vibrational mode-dependent diagonal anharmonicity was observed in transient infrared spectra, with a generally smaller anharmonicity found for the E mode in both the Mn and Re complexes. 相似文献
999.
Lemonnier JF Floquet S Marrot J Terazzi E Piguet C Lesot P Pinto A Cadot E 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(12):3548-3557
The influence of rigid or semirigid dicarboxylate anions, terephtalate (TerP(2-)), isophtalate (IsoP(2-)), and phenylenediacetate (PDA(2-)) on the self-condensation process of the [Mo(2)O(2)S(2)](2+) dioxothio cation has been investigated. Three new molybdenum rings, [Mo(12)O(12)S(12)(OH)(12)(TerP)](2-) ([Mo(12)TerP](2-)), [Mo(16)O(16)S(16)(OH)(16)(H(2)O)(4)(PDA)(2)](4-) ([Mo(16)(PDA)(2)](4-)), and [Mo(16)O(16)S(16)(OH)(16)(H(2)O)(2)(IsoP)(2)](4-) ([Mo(16)(IsoP)(2)](4-)) have been isolated and unambiguously characterized in the solid state by single-crystal X-ray studies and in solution by various NMR methods and especially by diffusion-correlated NMR ((1)H DOSY) spectroscopy, which was shown to be a powerful tool for the characterization and speciation of templated molybdenum ring systems in solution. Characterization by FT-IR and elemental analysis are also reported. The dynamic and thermodynamic properties of both the sixteen-membered rings were studied in aqueous medium. Specific and distinct behaviors were revealed for each system. The IsoP(2-)/[Mo(2)O(2)S(2)](2+) system gave rise to equilibrium, involving mono-templated [Mo(12)IsoP](2-) and bis-templated [Mo(16)(IsoP)(2)](4-) ions. Thermodynamic parameters have been determined and showed that the driving-force for the formation of the [Mo(16)(IsoP)(2)](4-) is entropically governed. However, whatever the conditions (temperature, proportion of reactants), the PDA(2-)/[Mo(2)O(2)S(2)](2+) system led only to a single compound, the [Mo(16)(PDA)(2)](4-) ion. The latter exhibits dynamic behavior, consistent with the gliding of both the stacked aromatic groups. Stability and dynamics of both Mo(16) rings was related to weak hydrophobic or pi-pi stacking inter-template interactions and inner hydrogen-bond network occurring within the [Mo(16)(IsoP)(2)](4-) and [Mo(16)(PDA)(2)](4-) ions. 相似文献
1000.
Catalyzing aldehyde hydrosilylation with a molybdenum(VI) complex: a density functional theory study
Costa PJ Romão CC Fernandes AC Royo B Reis PM Calhorda MJ 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(14):3934-3941
[MoCl(2)O(2)] catalyzes the hydrosilylation reaction of aldehydes and ketones, as well as the reduction of other related groups, in apparent contrast to its known behavior as an oxidation catalyst. In this work, the mechanism of this reaction is studied by means of density functional theory calculations using the B3LYP functional complemented by experimental data. We found that the most favorable pathway to the first step, the Si--H activation, is a [2+2] addition to the Mo=O bond, in agreement with previous and related work. The stable intermediate that results is a distorted-square-pyramidal hydride complex. In the following step, the aldehyde approaches this species and coordinates weakly through the oxygen atom. Two alternative pathways can be envisaged: the classical reduction, in which a hydrogen atom migrates to the carbon atom to form an alkoxide, which then proceeds to generate the final silyl ether, or a concerted mechanism involving migration of a hydrogen atom to a carbon atom and of a silyl group to an oxygen atom to generate the silyl ether weakly bound to the molybdenum atom. In this Mo(VI) system, the gas-phase free energies of activation for both approaches are very similar, but if solvent effects are taken into account and HSiMe(3) is used as a source of silicon, the classical mechanism is favored. Several unexpected results led us to search for still another route, namely a radical path. The energy involved in this and the classical pathway are similar, which suggests that hydrosilylation of aldehydes and ketones catalyzed by [MoCl(2)O(2)] in acetonitrile may follow a radical pathway, in agreement with experimental results. 相似文献