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1.
We report the structural and functional features of two new catalysts: a mononuclear [Fe(N5mpy)(CH3CN)](BF4)2 (N5mpy = (N,N′E,N,N′E)-N,N′-(pyridine-2,6-diylbis(ethan-1-yl-1-ylidene))bis(1-(pyridin-2-yl)methanamine)) complex and a binuclear {[Fe(N5mpy)]2O}(BF4)4 complex. Both compounds catalyze the oxidation of alkanes by H2O2, in MeCN or acetone to yield alcohols and ketones. Moderate to good yields are obtained with various cyclic and benzylic alkanes. Screening of several substrates revealed that higher yields are obtained for the oxidation of alkanes with low C–H bond dissociation energies. The ratio alcohol/ketone observed suggests the involvement of iron-based oxidizing species.  相似文献   

2.
The Ca(B′1/2Ta1/2)O3 [B′=La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Y, Er, Yb, and In] double perovskite-type ceramics have been prepared by the conventional solid-state ceramic route. The phase purity and surface morphology of the sintered ceramics have been studied by X-ray diffraction (XRD) and scanning electron microscopy methods. XRD study revealed intersubstitution between Ca and B′ ions. Ca(B′1/2Ta1/2)O3 ceramics have relative permittivity (ɛr) in the range 23–30, normalized quality factor (Qu×f) 20 600–59 200 GHz, and temperature coefficient of resonant frequency (τf) −6 to −35 ppm/°C. The dielectric properties of Ca(B′1/2Ta1/2)O3 ceramics have been tailored by the addition of positive τf materials such as CaTiO3, TiO2, Ba(Y1/2Ta1/2)O3, and Ba(Yb1/2Ta1/2)O3, which form a solid solution or a mixture phase with the parent compound. The 0.7Ca(Y1/2Ta1/2)O3–0.3Ba(Y1/2Ta1/2)O3 ceramic has ɛr=27.5, Qu×f=41 900 GHz, and τf=−1.2 ppm/°C, and the 0.6Ca(Yb1/2Ta1/2)O3–0.4Ba(Yb1/2Ta1/2)O3 ceramic has ɛr=27.7, Qu×f=48 000 GHz, and τf=1.8 ppm/°C.  相似文献   

3.
A bimetallic supramolecular coordination polymer; {[(Me3Sn)8Ag4(OH)4(CN)8(tbpe)](tbpe)} n , 1, was obtained by the reaction in situ of K2[Ag(CN)2] with Me3SnCl and trans-1,2-bis(4-pyridyl)ethene (tbpe) in a H2O/MeCN/NH3 solvent. The structure of 1 consists of discrete puckered tetranuclear chains comprising {[(Me3Sn)4Ag2(OH)2(CN)4]2(tbpe)} in addition to one template free tbpe ligand. In these chains, the bridging hydroxyl group and the bipodal tbpe ligand are used to give two novel spacers based on the organometallic Me3Sn unit; i.e., a longer spacer [–CN–(Me3)Sn–O(H)–(Me3)Sn–L–(Me3)Sn–O(H)–(Me3)Sn–NC–] with a separation distance of 31.29 Å, and a relatively shorter spacer [–CN–(Me3)Sn–O(H)–(Me3)Sn–NC–] with a separation distance of 14.431 Å. Supramolecular interactions such as hydrogen bonding, π–π stacking, cation···π interactions, play a prominent role in the assembly of this compound. The structure of the SCP was also investigated by FTIR and electronic absorption spectra and thermal analysis and the data are compared to the prototype compounds. The SCP 1 exhibits strong fluorescence in acetonitrile and shows specific in vitro antitumor activity against human breast cancer cell line, MCF7.  相似文献   

4.
A class of novel cationic Gemini imidazolium surfactants containing amide groups as the spacer were synthesized from ethylenediamine and 1-bromoalkane(C8, C10, C12, C14, C16) by N-alkylation to get N,N′-dialkyl ethylenediamine (1a–e), 1a–e was further reacted with chloroacetyl chloride by N-acylation to get N,N′-(ethane-1,2-diyl)bis(2-chloro-N-alkylacetamide) (2a–e), which was further reacted respectively with 1-methyl imidazole by quaternized to form the surfactant molecule, N,N′-((ethane-1,2-diyl)bis(alkyl-azanediyl)bis(2-oxoethane-2,1-diyl)) bis(1-methyl-1H-imidazol-3-ium) dichloride. The structures of intermediates (1a–e) and (2a–e) were characterized by IR and 1H NMR. The structures of the surfactants (3a–e) were characterized by IR, 1H-NMR and 13C-NMR and element analysis. The critical micelle concentrations (CMC) of 3a–e were determined by the conductivity method at 25 °C. The CMC values decreased with increasing the length of the hydrophobic chain. The surfactants (3a–e) showed good foaming stability, emulsion ability and wetting ability. The surfactants (3a–e) also have good antimicrobial activity against Staphylococcus aureus, Escherichia coli and Bacillus subtilis.  相似文献   

5.
The third‐generation peptide‐dendrimer B1 (AcES)8(BEA)4(K‐Amb‐Y)2BCD‐NH2 (B=branching (S)‐2,3‐diaminopropanoic acid, K=branching lysine, Amb=4‐aminomethyl‐benzoic acid) is the first synthetic model for cobalamin‐binding proteins and binds cobalamin strongly (Ka=5.0×106 M ?1) and rapidly (k2=346 M ?1 s?1) by coordination of cobalt to the cysteine residue at the dendrimer core. A structure–activity relationship study is reported concerning the role of negative charges in binding. Substituting glutamates (E) for glutamines (Q) in the outer branches of B1 to form N3 (AcQS)8(BQA)4(B‐Amb‐Y)2BCD‐NH2 leads to stronger (Ka=12.0×106 M ?1) but slower (k2=67 M ?1 s?1) cobalamin binding. CD and FTIR spectra show that the dendrimers and their cobalamin complexes exist as random‐coil structures without aggregation in solution. The hydrodynamic radii of the dendrimers determined by diffusion NMR either remains constant or slightly decreases upon binding to cobalamin; this indicates the formation of compact, presumably hydrophobically collapsed complexes.  相似文献   

6.
A phosphine-stabilized mononuclear gold complex Au(PPh3)(NO3) (1) and a phosphine-stabilized gold cluster [Aug(PPh3)8](NO3)3 (2) were used as precursors for preparation of supported gold catalysts. Both complexes 1 and 2 supported on inorganic oxides such as -Fe2O3, TiO2, and SiO2 were inactive for CO oxidation, whereas the 1 or 2/ oxides treated under air or CO or 5% h2/Ar atmosphere were found to be active for CO oxidation. The catalytic activity depended on not only the treatment conditions but also the kinds of the precursor and the supports used. The catalysts derived from 1 showed higher activity than those derived from 2. -Fe2O3 and TiO2 were much more efficient supports than SiO2 for the gold particles which were characterized by XRD and EXAFS.  相似文献   

7.
The influence of different rare earth oxide additives (La2O3, Nd2O3, Sm2O3, Y2O3, Yb2O3 and Lu2O3) on the oxidation behaviour of carbon derived Si3N4–SiC micro-nanocomposites has been investigated. All investigated composites exhibited predominately parabolic oxidation behaviour indicated diffusion as the rate limiting mechanism. Except the Si3N4–SiC composite sintered with Lu2O3 the rate-limiting oxidation mechanism for all other materials was an outward diffusion of the additive cations along the grain boundary towards the surface. Such diffusion of cation has been strongly suppressed in the Lu-doped composite because of the beneficial effect of stable grain boundary phase and the presence of the SiC particles predominately located at the grain boundaries of Si3N4. Nanoparticles at the grain boundaries act as the obstacles for migration of cations of the additives resulting in superior oxidation resistance of Si3N4–SiC–Lu2O3 where the rate-limiting step is inward diffusion of oxygen through the oxide layer to the bulk ceramics.  相似文献   

8.
Comment     
Electrolytic manganese dioxide is dissolved in the mixed non-aqueous solvent dimethyl sulfoxide–sulfur dioxide (DMSO–SO2) to form manganese disulfate as a final product. Sulfur dioxide does not change the oxidation state of the metal cations in DMSO–SO2 solvent. However, oxidation of sulfur(IV) to sulfur(VI) is possible. The complete MnO2 dissolution occurs in 50 min at a stirring speed of 650 rpm, pH 1, 0.2% solids concentration, 35 × 44 mesh particle size, and 36°C. IR and FTIR evidence has been presented in favor of the formation of SO, S2O, (CH3)2S+ as intermediate species for the proposed mechanism. In the mixed non-aqueous solvent system the kinetics of leaching is controlled by a mass transport process. The equation 1–?α–(1–α)2/3 = kt fits the experimental data very well. This is further supported by scanning electron micrographs, which show a product layer formation on the surface of the MnO2 particle, and by the dependence of k on 1/r.  相似文献   

9.
The oxidative polycondensation reaction conditions of 4‐[(pyridine‐3‐yl‐methylene) amino]phenol (4‐PMAP) were studied using H2O2, atmospheric O2, and NaOCl oxidants in an aqueous alkaline medium between 30°C and 90°C. Synthesized oligo‐4‐[(pyridine‐3‐yl‐methylene) amino] phenol (O‐4‐PMAP) was characterized by 1H‐, 13C NMR, FTIR, UV–vis, size exclusion chromatography (SEC), and elemental analysis techniques. The yield of O‐4‐PMAP was found to be 32% (for H2O2 oxidant), 68% (for atmospheric O2 oxidant), and 82% (for NaOCl oxidant). According to the SEC analysis, the number–average molecular weight, weight–average molecular weight, and polydispersity index values of O‐4‐PMAP was found to be 5767, 6646 g mol?1, and 1.152, respectively, using H2O2, and 4540, 5139 g mol?1, and 1.132, respectively, using atmospheric O2, and 9037, 9235 g mol?1, and 1.022, using NaOCl, respectively. According to TG and DSC analyses, O‐4‐PMAP was more stable than 4‐PMAP against thermal decomposition. The weight loss of O‐4‐PMAP was found to be 94.80% at 1000°C. Also, antimicrobial activities of the oligomer were tested against B. cereus, L. monocytogenes, B. megaterium, B. subtilis, E. coli, Str. thermophilus, M. smegmatis, B. brevis, E. aeroginesa, P. vulgaris, M. luteus, S. aureus, and B. jeoreseens. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3327–3333, 2006  相似文献   

10.
According to the properties determined for the ternary end‐members, MAX phases in the quaternary Cr–Ti–Al–C system could be of interest as protective coatings for nuclear fuel cladding in the case of severe accident conditions. In this study, syntheses of 211 and 312 MAX phase compositions were attempted using pressureless reactions starting from Cr, TiH2, Al, and C (graphite) powders. It was observed that both the Ti substitution by Cr in Ti3AlC2 and the mutual solubility of Ti2AlC and Cr2AlC are limited to a few atomic percent. In addition, the remarkable stability of the (Cr2/3Ti1/3)3AlC2 MAX phase composition was confirmed. Due to the low miscibility of MAX phases in the Cr–Ti–Al–C system, most samples contained substantial amounts of TiCx and Al–Cr alloys as secondary phases, thus forming composite materials. After sintering, all samples were submitted to a single oxidation test (12 h at 1400°C in air) to identify compositions potentially offering high‐temperature oxidation resistance and so warranting further investigation. In addition to (Cr0.95Ti0.05)2AlC, composite samples containing substantial quantities of Al8Cr5 and AlCr2 formed a stable and passivating Al2O3 scale, whereas the other samples were fully oxidized.  相似文献   

11.
A new semidry flue gas desulfurization (FGD) process is proposed. The process uses a magnetically fluidized bed (MFB) as the reactor in which ferromagnetic particles are fluidized with simulated flue gas under the influence of an external magnetic field. A slurry of lime is continuously sprayed into the reactor by an atomizer fixed at the top of the bed. As a consequence, the desulfurization reaction and slurry drying take place simultaneously in a same reactor. Experiments with a laboratory‐scale apparatus were carried out to investigate the roles of the ferromagnetic particles and the magnetic field applied in the desulfurization reaction. The results show that when ferromagnetic particles are used as the fluidization material, both sulfite (SO32–) salts and sulfate (SO42–) salts are found in the desulfurization products. When quartz particles are used, only sulfite (SO32–) salts are found. This suggests that the Fe(III) ions and Fe(II) ions result from the ferromagnetic particles dissolving in the liquid phase. In addition, the ions act as catalysts in the oxidation of S(IV) to S(VI) and react with SO2 producing FeSO3 and Fe2(SO4)3 as the products. On the other hand, the level of the sulfate (SO42–) salts in the products increases with increasing intensity of applied field intensity, which suggests that the oxidation of S(IV) can be enhanced by the applied magnetic field. The oxidation of S(IV) can increase the solubility of SO2, and therefore, intensify the reaction between SO2 and Ca(OH)2, leading to an increased SO2 removal efficiency.  相似文献   

12.
The reactions between dithizone (H2Dz, (1)) or potassium dithizonate (K+HDz, (2)) and phenylmercury(II) chloride gives PhHg(HDz), (3). Complex (3) is photochromic. In dichloromethane, the blue photo-exited state of (3) exhibits a first order relaxation process to regenerate the orange ground state with rate constant 0.00053 s−1. The half life of this relaxation is ca. 1300 s. Electrochemically, on cyclic voltammetry time scale, the oxidations of (1) and (3) are different. A comparative voltammetric and spectro-electrochemical study of (1) and (3) in CH2Cl2 containing 0.1 mol dm−3 [N(nBu)4][B(C6F5)4] revealed that the mercapto group of (1) can be oxidised in two one-electron transfer steps. A disulphide is first produced and then in a second oxidation step, HDz+ is formed. In contrast, complex (3) shows only one ligand-based oxidation step. Upon complexation with phenylmercury the free mercaptan group of (1) becomes a stable “metal thioether”, Hg–S–C, which effectively prevents disulphide formation in (3) upon electrochemical oxidation. Both (1) and (3) shows two reduction steps. The electrochemical fingerprint of blue photo-excited (3) is identical to that of the orange ground state as no new functional groups are introduced upon irradiation; only bond rotation occurs. The different electronic spectra for each of the redox states of (3), obtained from spectro-electrochemical measurements, revealed that only the (3)/(3) couple exhibits electrochromic properties.  相似文献   

13.
Owing to the high melting points and high-temperature stability, transition-metal disilicides are potential components for aerospace, automotive, and industrial engineering applications. However, unwanted oxidation known as PEST oxidation severely limits their application owing to the formation of volatile transition metal oxides, especially in the temperature range of 500–1000 °C. To overcome this problem, a new class of high-entropy disilicides, (Mo0.2Nb0.2Ta0.2V0.2W0.2)Si2, was selected by first-principles calculations and then successfully fabricated using a hot-pressing sintering technique. Furthermore, the phase evolution, thermal expansion behavior, thermal conductivity, and oxidation behavior were systematically investigated. Compared with MoSi2, (Mo0.2Nb0.2Ta0.2V0.2W0.2)Si2 possessed a lower thermal conductivity (10.9–14.7 W·m?1·K?1) at 25–1000 °C, higher thermal expansion coefficients (8.6 ± 1.3–6 K–1) at 50–1200 °C, and especially an excellent thermal stability at 500–1000 °C owing to slow diffusion and selective oxidation. This work provides a strong foundation for the synthesis and application of high-entropy disilicides.  相似文献   

14.
Reduction of methyl 8-hydroxy-11-E/Z-octadecen-9-ynoate (1) with zinc in either aqueous n-propanol or water under concomitant ultrasound irradiation furnished a mixture of methyl 8-hydroxy-9Z,11E-octadecadienoate (3a) and methyl 8-hydroxy-9Z, 11Z-octadecadienoate (3b) (96% yield). Reduction of methyl 8-oxo-11-E/Z-octadecen-9-ynoate (2) under similar conditions gave methyl 8-oxo-10-Z-octadecenoate exclusively (4, 70%). The latter compound was epoxidized and converted to a C18 furanoid fatty ester (6, methyl 8,11-epoxy-8,10-octadecadienoate) in 70% yield.  相似文献   

15.
A novel method is developed for low temperature synthesis of carbon encapsulated spherical Fe7S8, equiaxed Fe3O4 and spherical porous FeOOH nanocrystals with a core–shell structure via a solid–solid reaction of ferrocene with (NH4)2S2O8, (NH4)2Cr2O7 and NH4ClO4 in an autoclave, respectively. Samples were characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. It is found that the median size of Fe7S8, Fe3O4 and FeOOH nanocrystals is about 28.99, 52.68 and 25.66 nm, respectively. The hollow worm-like carbon shell provides exclusive rooms for tens to hundreds of nanocrystals separated from each other. The cooperative effect of ammonium and strong oxidizing ion on electrophilic oxidation of ferrocene contributes to the in situ formation of carbon shell on the nanocrystals. The metal–π interaction of iron atom with cyclopentadienone oligomers enables ordered self-assembling of carbon rings, resulting in the formation of graphitizable carbon shell with roughly parallel fringes at low temperature.  相似文献   

16.
The medium-entropy oxide (Y1/3Yb1/3Lu1/3)2O3 with a body-centered cubic structure was successfully synthesized by solid-state reaction process, and then it was introduced into SiC ceramic to study its effect on the oxidation behavior of SiC ceramic at 1700 °C. The (Y1/3Yb1/3Lu1/3)2O3-modified SiC ceramic exhibited better oxidation resistance than its individual oxides (Y2O3, Yb2O3, and Lu2O3) modified SiC ceramic. The experimental and calculated results all indicate that the rare-earth atoms had the tendency to diffuse into the SiO2 structure and occupy the interstitial positions within SiO2 structure. The introduction of medium-entropy oxide (Y1/3Yb1/3Lu1/3)2O3 reduced the initial oxidation rate of the ceramic samples (1?3 h), and enhanced the stability of SiO2 structure, thus resulting in a better oxidation resistance at 1700 °C.  相似文献   

17.
《Ceramics International》2016,42(8):9836-9843
Metals and alloys (such as Al, Si, Al–Mg and Al–Si) are commonly added to MgO–C refractory bricks as antioxidants due to their effectiveness to prevent carbon oxidation (in the 600–1400 °C range) and their low cost. These additives act at different temperatures and react with refractory components and gases in the environment, inducing significant changes in the resultant microstructure and affecting the overall thermo-mechanical performance of these products. This work addresses the evaluation of physical properties, cold and hot mechanical resistance, as well as in situ hot elastic modulus (E) measurements in the temperature range of 30–1400 °C for MgO–C bricks containing antioxidants (Al, Si or Al–Mg alloy) in a reducing atmosphere. Cured and fired samples of the designed formulations were evaluated throughout 1 or 2 heating-cooling cycles. Despite the improved mechanical behavior (higher cold crushing strength and hot modulus of rupture) of the antioxidant-containing formulations, compared to the additive-free MgO–C sample, the interaction of the selected additives with the refractory components and CO(g) led to a generation of phases (i.e., Al4C3, Al2O3, SiC, SiO2, MgAl2O4) that could not be well accommodated in the microstructure. Consequently, the in situ E drop was observed during cooling (mainly below 600 °C) of the antioxidant-containing sample due to crack and flaw formations. Si and Al–Mg were the most promising antioxidants, whereas the Al-containing composition showed the highest E damage level after two heating/cooling cycles up to 1400 °C for cured samples. Based on the elastic modulus profiles with the temperature, the results also indicated the best working conditions for these ceramic materials.  相似文献   

18.
Two novel late transition metals complexes with bidentate O?N chelate ligand, Mt(benzocyclohexan‐ketonaphthylimino)2 {Mt(bchkni)2: bchkni ?C10H8(O)C[N(naphthyl)CH3]; Mt ? Ni, Pd}, were synthesized. In the presence of B(C6F5)3, both complexes exhibited high activity toward the homo‐polymerization of norbornene (NB) (as high as 2.7 × 105 gpolymer/molNi·h for Ni(bchkni)2/B(C6F5)3 and 2.3 × 105 gpolymer/molPd·h for Pd(bchkni)2/B(C6F5)3, respectively). Additionally, both catalytic systems showed high activity toward the copolymerization of NB with 1‐octene under various polymerization conditions and produced the addition‐type copolymer with relatively high molecular weights (0.1–1.4 × 105g/mol) as well as narrow molecular weight distribution. The 1‐octene content in the copolymers can be controlled up to 8.9–14.0% for Ni(bchkni)2/B(C6F5)3 and 8.8–14.6% for Pd(bchkni)2/B(C6F5)3 catalytic system by varying comonomer feed ratios from 10 to 70 mol %. The reactivity ratios of two monomers were determined to be r1‐octene = 0.052, rNB = 8.45 for Ni(bchkni)/B(C6F5)3 system, and r1‐octene = 0.025, rNB = 7.17 for Pd(bchkni)/B(C6F5)3 system by the Kelen‐TÜdÕs method. The achieved NB/1‐octene copolymers were confirmed to be noncrystalline and exhibited good thermal stability (Td > 400°C, Tg = 244.1–272.2°C) and showed good solubility in common organic solvents. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013  相似文献   

19.
Spin Trapping of Radicals Formed during the Decomposition of Aromatic Diazonium Salts by Ultrasound The decomposition of aromatic diazonium compounds ArN2X (Ar = phenyl, 2,5-diethoxy-4-(N-morpholino)phenyl; X = BF4, PF6, B(C6H5)4, SCN, OCN,N3; 1a , 1c–f , 2b–f ) by ultrasonic waves has been studied by e.s.r. The spin trapping technique has been shown to be a suitable method for the detection of free radical intermediates.  相似文献   

20.
Three antimony-containing polymers (P1, P2, P3) were synthesized by reacting triphenyl antimony dinitrate with bisphenol A (P1), with tetrabromobisphenol A (P2) and with N,N′-bis(4-hydroxybenzylidene)-oxydianiline (P3). Solubility, density, chemical and thermal stability of these antimony polymers have been evaluated. The polymers are only soluble in dipolar aprotic solvents like dimethyl sulfoxide, dimethylformamide, dimethylacetamide, etc., and have relatively high densities (1.2–1.8 g cm–3). The solubility parameters (δ) and chemical stability of the polymers were studied in different chemical environments. The thermal properties of the polymers have been studied by thermogravimetric analysis, differential thermal analysis and isothermal gravimetric analysis.  相似文献   

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