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1.
《Comptes Rendus Chimie》2015,18(10):1143-1151
Two series of carbon-supported Pd–Au catalysts were prepared by the reverse “water-in-oil, W/O” method, characterized by various techniques and investigated in the reaction of tetrachloromethane with hydrogen at 423 K. The synthesized nanoparticles were reasonably monodispersed having an average diameter of 4–6 nm (Pd/C and Pd–Au/C) and 9 nm (Au/C). Monometallic palladium catalysts quickly deactivated during the hydrodehalogenation of CCl4. Palladium–gold catalysts with molar ratio Pd:Au = 90:10 and 85:15 were stable and much more active than the monometallic palladium and Au-richer Pd–Au catalysts. The selectivity toward chlorine-free hydrocarbons (especially for C2+ hydrocarbons) was increased upon introducing small amounts of gold to palladium. Simultaneously, for the most active Pd–Au catalysts, the selectivity for undesired dimers C2HxCly, which are considered as coke precursors, was much lower than for monometallic Pd catalysts. Reasons for synergistic effects are discussed. During CCl4 hydrodechlorination the Pd/C and Pd–Au/C catalysts were subjected to bulk carbiding.  相似文献   

2.
Synthesis and physico-chemical characterization of a pure magnesium phosphate (MgP) prepared by coprecipitation, and MgP modified by introduction of cobalt–molybdenum (4–12 wt.% of MoO3 with the Co/Mo ratio fixed at 0.5) have been carried out. The structural properties of these catalysts were characterized by X-ray diffraction, their textural properties were determined by N2 adsorption–desorption isotherms and the dispersion of cobalt–molybdenum was studied by XPS spectroscopy. Their acid properties have been investigated by in situ FT-IR spectroscopy of adsorbed molecules, often, 2,6-dimethylpyridine (pKa = 6.7), pyridine (pKa = 5.3). Co–Mo incorporation leads to a modification in the MgP acid–base properties, especially on the acid sites type and number. Thus, lower loading of cobalt–molybdenum species decreased the number of strong Lewis acid sites whereas higher loading increased it. It was found that Lewis acid sites on magnesium phosphates play an important role in the isomerization of 3,3-dimethylbut-1-ene.The 3,3-dimethylbut-1-ene (33DMB1) conversion increases with the reaction temperature from 493 to 653 K for MgP, but decreases after 573 K for MgP supported by Co–Mo. A linear relationship between both types of acid sites and conversion values was found. The deactivation of the catalysts appears at high reaction temperature (>573 K).  相似文献   

3.
Stable, insoluble Langmuir monolayer films composed of Staphylococcus aureus-specific lytic bacteriophage were formed at an air–water interface and characterized. The phage monolayer was very strong, withstanding a surface pressure of ~40 mN/m at 20 °C. The surface pressure–area (ΠA) isotherm possessed a shoulder at ~7 × 104 nm2/phage particle, attributed to a change in phage orientation at the air–water interface from horizontal to vertical capsid-down/tail-up orientation as surface pressure was increased. The ΠA-dependence was accurately described using the Volmer equation of state, assuming horizontal orientation to an air–water interface at low surface pressures with an excluded area per phage particle of 4.6 × 104 nm2. At high pressures phage particles followed the space-filling densely packed disks model with a specific area of 8.5 × 103 nm2/phage particle. Lytic phage monolayers were transferred onto gold-coated silica substrates from the air–water interface at a constant surface pressure of 18 mN/m by Langmuir–Blodgett method, then dried and analyzed by scanning electron microscopy (SEM) and ellipsometry. Phage specific adsorption (Γ) in Langmuir–Blodgett (LB) films measured by SEM was consistent with that calculated independently from Π–A isotherms at the transfer surface pressure of 18 mN/m (Γ = 23 phage particles/μm2). The 50 nm-thickness of phage monolayer measured by ellipsometer agreed well with the horizontal phage average size estimated by SEM. Surface properties of phage Langmuir monolayer compare well with other monolayers formed from nano- and micro-particles at the air–water interface and similar to that of classic amphiphiles 1,2-diphytanoyl-sn-glycero-3-phosphocholine (phospholipid) and stearic acid.  相似文献   

4.
《Tetrahedron: Asymmetry》2007,18(22):2625-2631
The iridium complex-catalyzed asymmetric hydrogenation of quinolines in a DMPEG/hexane biphasic system was studied. Catalysts with C2-symmetric ligands such as Xyl-P-Phos, Cl–MeO–BIPHEP, SYNPHOS, and DifluorPhos are highly effective for this type of reaction. Most of the catalysts tested can be retained in DMPEG (Mn = 500), and the asymmetric hydrogenation of various quinoline substrates can be carried out in DMPEG/hexane biphasic system with up to 92% ee. The catalysts and the products can be separated via simple phase separation, and the reactivity/stereoselectivity of the catalysts can be retained for at least three reaction cycles.  相似文献   

5.
A general and highly efficient trifluoromethylated-N-heterocyclic carbene (NHC)-based catalyst for the palladium-catalyzed Suzuki–Miyaura reaction was reported. In the presence of the catalyst, reactions of non-activated aryl chlorides and triflates with aryl boronic acids occurred at room temperature with good to excellent yields (63–98%). In addition, catalysts generated from a combination of Pd(OAc)2/imidazolium salt 6a is not only effective for the coupling of heteroaryl boronic acid with aryl halides and heteroaryl halides, but also efficient for coupling of other heteroaryl halides and heteroaryl boronic acids. Finally, the catalyst is highly effective for Suzuki–Miyaura reaction of aryl bromides and chlorides with 0.01–0.1 mol % loading if the temperature was raised at refluxed THF/H2O.  相似文献   

6.
《Tetrahedron: Asymmetry》2014,25(4):334-339
Herein we describe the preparation and characterization of a recoverable catalyst for a Henry reaction based on a Cu(II) complex of block copolymer α-methoxypoly(ethylene glycol)-b-poly(l-glutamic acid) with (2R,5S)- or (2S,5R)-5-isopropyl-5-methyl-2-(pyridine-2-yl)imidazolidine-4-one. The reactions of substituted aldehydes with nitromethane catalyzed by these catalysts proceed with high chemical yield (70–98%) and with high enantioselectivity (61–92% ee). The reaction mixture is in the form of a colloid system and is formed by self-organized aggregates of the catalysts with average hydrodynamic particle size of 189 ± 3 nm (DLS). After sevenfold recycling, the catalyst exhibited no decrease in the enantioselectivity and only a slight decrease (ca. 18%) in the yield for the Henry reaction of nitromethane with 2-methoxybenzaldehyde.  相似文献   

7.
Catalytic generation of hydrogen by steam reforming of acetic acid over a series of Ni–Co catalysts have been studied. The catalyst with the molar ratio of 0.25:1 between Ni and Co was superior to other catalysts. The effects of reaction temperature, liquid hourly space velocity (LHSV) and molar ratios of steam-to-carbon (S/C) were studied in detail over this catalyst. At T = 673 K, LHSV = 5.1 h−1, S/C = 7.5:1, the catalyst exhibited the best performances. Acetic acid was converted completely to hydrogen, while H2 selectivity reached up to 96.3% and CO2 selectivity up to 98.1% was obtained, respectively. Ni–Co catalyst showed rather stable performances for the 70 h time-on-stream without any deactivation.  相似文献   

8.
The synthesis of new ruthenium-based catalysts applicable for both homogeneous and heterogeneous metathesis is described. Starting from the Hoveyda-Grubbs first generation (1) and the Hoveyda-Grubbs second generation (2) catalysts the homogeneous catalysts [RuCl((RO)3Si–C3H6–N(R′)–CO–C3F6–COO)(CH–o-O–iPr–C6H4)(SIMes)] (4: R = Et, R′ = H; 5: R = R′ = Me) (SIMes = 1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene) were prepared by substitution of one chloride ligand with trialkoxysilyl functionalized silver carboxylates (RO)3Si–C3H6–N(R′)–CO–C3F6–COOAg (3a: R = Et, R′ = H; 3b: R = R′ = Me). These homogeneous ruthenium-species are among a few known examples with mixed anionic ligands. Exchange of both chloride ligands afforded the catalysts [Ru((RO)3Si–C3H6–N(R′)–CO–C3F6–COO)(CH–o-O–iPr–C6H4)(SIMes)] (9: R = Et, R′ = H; 11: R = R′ = Me) and [Ru((RO)3Si–C3H6–N(R′)–CO–C3F6–COO)(CH–o-O–iPr–C6H4)(PCy3)] (8: R = Et, R′ = H; 10: R = R′ = Me). The reactivity of the new complexes was tested in homogeneous ring-closing metathesis (RCM) of N,N-diallyl-p-toluenesulfonamide and TONs of up to 5000 were achieved. Heterogeneous catalysts were obtained by reaction of 4, 5 and 811 with silica gel (SG-60). The resultant supported catalysts 4a, 5a, 8a11a showed reduced activity compared to their homogenous analogues, but rival the activity of similar heterogeneous systems.  相似文献   

9.
The influence of bismuth addition on the activity and selectivity of palladium catalysts supported on SiO2 in the reaction of glucose oxidation to gluconic acid was studied. The catalysts modified with Bi show much better selectivity and activity than palladium catalysts. The XRD studies proved the presence of intermetallic compounds BiPd and Bi2Pd, which probably increase activity and selectivity of PdBi/SiO2 catalysts in the oxidation of glucose. The TPO studies of catalysts containing 5 wt.% Pd/SiO2, 3 wt.% Bi/SiO2 and 5 wt.% Pd–5 wt.% Bi/SiO2 show that palladium oxidation occurs at much higher temperatures than in the case of bismuth. The maximum rate of Pd oxidation occurs at around 580 K while the maximum rate of Bi oxidation takes place at around 430 K. Considering the above facts, a reaction involving bimetallic catalysts in oxidizing atmosphere at 333 K should not lead to surface oxidation of palladium and thus their deactivation.  相似文献   

10.
《Vibrational Spectroscopy》2004,34(1):109-121
The applicability of a React-IR™ system, containing a diamond attenuated total reflection (ATR) crystal, in heterogeneous liquid-phase catalytic reactions was evaluated by analysis of the catalytic esterification of 1-octanol and hexanoic acid over a Nafion/silica catalyst in an open reflux configuration at atmospheric pressure. The reaction was performed in either cumene (at 427 K) or n-decane (at 447 K). The concentration profiles of the esterification reaction, as determined by this real-time in situ IR spectroscopic technique, are in qualitative and quantitative agreement with those determined by conventional off-line GC analysis.Interestingly, besides the bands assigned to the ester, alcohol, and acid, an additional strong and broad absorption band was observed at around 1100 cm−1 in the spectra during the esterification reaction in cumene (at 427 K). It was assessed by variation of the reaction mixture that this band is a result of the reaction of silica with octanol, yielding Si–O–R functionalities. The relevance of this reaction for the kinetics of the studied catalytic esterification, is discussed. More importantly, the contribution of solid particles and leached species to the 1100 cm−1 band is evaluated. Strong indications exist that solid catalyst particles are contributing to the spectra, implying that on-line analysis of intermediate species adsorbed on heterogeneous catalysts is in specific cases possible using the React-IR™ technique.  相似文献   

11.
A new approach to test fuel cell catalysts under conditions of high mass transport and variable temperature is described. This approach relies upon utilising a 5 μm thick gold grid to act as a catalyst support in contact with a perfluorsulfonic acid (PFSA) membrane in a true three electrode electrochemical configuration. The gold grid has 20 μm × 20 μm sized holes in it which allow the reactant gas to reach the catalyst layer. The high electrical conductivity and low profile of the grid ensure that electrical and mass transport losses are minimal. We have used this configuration to look at the oxygen reduction reaction (orr) and the hydrogen oxidation reaction (hor) on a platinum-black and platinum on carbon catalyst at a loading of about 10 μg cm−2. We find that for the orr we can measure kinetic currents over the entire range of relevant fuel cell operating potentials (0.55–1 V). Although platinum-black shows higher specific catalytic activity towards the orr than platinum on carbon at high potentials, this performance benefit is reduced at lower potentials. For the hor we measure exchange current densities of 0.022 A cm−2 and 0.026 A cm−2 respectively on the Pt-Black and Pt/C. These values indicate that there does not appear to be a size effect for the hor, unlike the orr.  相似文献   

12.
Dealloyed PtAg/C nanostructures, prepared by selective electrochemical etching of Ag in 0.5 M H2SO4 from a series of alloyed PtmAg/C samples with atomic Pt/Ag ratio m = 0.1, 0.5, 1.0 and 1.5, were employed as cathode electrocatalysts for oxygen reduction reaction (ORR) in 0.5 M KOH. Compared with their as-prepared counterpart alloy catalysts, the dealloyed catalysts showed higher half-wave potentials (E1/2) and significantly higher Pt mass-specific activity (MSA) data. The intrinsic activity (IA) of Pt increased more or less after the dealloying treatment but was strongly dependent on the composition (m) of the alloyed sample. The Pt IA numbers were comparable for the dealloyed catalysts derived from PtmAg/C of m = 0.5, 1.0 and 1.5, which were nearly twice that for E-TEK Pt/C catalyst and 3 times that for the dealloyed catalyst derived from Pt0.1Ag/C.  相似文献   

13.
《Comptes Rendus Chimie》2015,18(12):1264-1269
A one-step CO2 hydrogenation reaction into hydrocarbons (HC) using a bifunctional system constituted by a methanol synthesis catalyst [Cu–ZnO–Al2O3 (CZA)] and a zeolite (HZSM-5) has been studied. The influence of the catalyst bed configuration on activity, selectivity, and HC yield has been evaluated. The results obtained at TR = 623 K, PR = 3.0 MPa and WHSV = 6000 h−1 show that CO2 hydrogenation and hydrocarbon selectivity were strongly influenced by the proximity between oxide and zeolite, whatever the disposition of the two catalytic active sites. Indeed, the highest conversion and the best yield of hydrocarbons (mainly C2) were obtained with the M1 bifunctional catalysts in which the oxide–zeolite proximity is the lowest. This is ascribed to the hydrogen spillover phenomenon, which does not promote the carbon chain growth.  相似文献   

14.
《Comptes Rendus Chimie》2015,18(4):374-378
An efficient methodology for obtaining 2-arylpyrimidines based on the use of p-sulfonic acid calix[6]arene as an organocatalyst is proposed. The methodology involves the formation of 1,2-dihydropyridine intermediates using a variety of aromatic aldehydes with methyl or ethyl acetoacetate and ammonium acetate, which are the same starting materials as in the Hantzsch reaction, under solvent-free reaction conditions, at 25 °C, followed by air oxidation for 12 h. The catalyst efficiency is not compromised after its successive use in reactions. Eleven examples were obtained with very good to excellent yields of 2-arylpyridines (92–62%). This is the first report about the use of calixarenes as catalysts in the multicomponent synthesis of 2-arylpyridines (molecules with potential biological activity).  相似文献   

15.
Cyanamide was used in the preparation series of metal–nitrogen–carbon (M–N–C) oxygen reduction catalysts. The best catalyst, treated at 1050 °C, shows good performance versus previously reported non-precious metal catalysts with an OCV ~ 1.0 V and a current density of 105 mA/cm2 (iR-corrected) at 0.80 V in H2/O2 fuel cell testing (catalyst loading: 4 mg cm? 2). Although nitrogen content has been previously correlated positively with ORR activity, no such trend is observed here for any nitrogen type. The combined effects of nitrogen and sulfur incorporation into the carbon may account for the high activity of the 1050 °C catalyst.  相似文献   

16.
《Supramolecular Science》1998,5(3-4):349-355
X-ray reflectivity (XR) measurements were carried out for amphiphilic diblock copolymer monolayers on water surface. From XR data, the layer thickness, and surface and interface roughnesses could be determined as a function of surface pressure. The XR experiments were performed using an ‘Air–Water Interface X-ray Reflectometer’ with conventional X-ray source (Cu target) in our laboratory. LB trough was equipped to the reflectometer, so the in situ measurements could be carried out for spread monolayers on water surface at different surface pressures. Kiessig fringes were observed for specular measurement for amphiphilic diblock copolymer, poly(α-methylstyrene)-poly(decyl 4-vinylpyridine) (P(α MSt)-b-P(4VP-C10H21I)) monolayers on water surface. It was observed that the thickness of the monolayer became thicker with increasing surface pressure. By curve fitting for the data obtained for the monolayer at surface pressure of 37 mN m-1, the thicknesses of P(αMSt)50 and P(4VP-C10H21I)50 layers was determined to be 21 and 22 Å, respectively. Because the chain length of P(αMSt)50 is calculated to be 126 Å in all-trans conformation, it was indicated that the molecules did not get aligned even when they were pressedto become such a dense state.  相似文献   

17.
In this work, some novel sulfonic acid functionalized imidazolium salts (SAFIS), as a new category of ionic liquids, are synthesized by eco-friendly and simple procedures, and used as highly efficient and reusable catalysts to promote the following one-pot multicomponent organic transformations under solvent-free conditions: (i) the synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes from β-naphthol (2 eq.) and arylaldehydes (1 eq.), (ii) the preparation of tetrahydrobenzo[a]xanthene-11-ones from β-naphthol, arylaldehydes and dimedone, and (iii) the synthesis of 1,8-dioxo-octahydroxanthenes from dimedone (2 eq.) and aromatic aldehydes (1 eq.). Environmentally benign, simple methodologies, easy workup procedure, clean reaction, short reaction time, high yield and easy preparation of the catalysts are some advantages of this work.  相似文献   

18.
Novel silver nanoparticles immobilized on macroporous polybenzoxazine nanocomposites were prepared as catalysts for catalytic reduction reaction.  相似文献   

19.
Some oxide catalysts, such as RuO2/Ti, IrO2/Ti and IrM(M: Ru, Mo, W, V)Ox/Ti binary oxide electrodes, were prepared by using a dip-coating method on a Ti substrate. Their catalytic behavior for the oxygen reduction reaction (ORR) was evaluated by cyclic voltammetry in 0.5 M H2SO4 at 60 °C. These catalysts were found to exhibit considerably high activity, and the most active one among them was Ir0.6V0.4O2/Ti prepared at 450 °C, showing onset potential for the ORR at about 0.86 V–0.90 (vs RHE).  相似文献   

20.
The ring-methylation of pyrrole or indole using supercritical methanol proceeded at 623 K without the further addition of catalysts. Pyrrole produced a mixture of unreacted pyrrole and mono-, di-, tri-, and tetra-methylpyrroles at the reaction time of 8 h. On the other hand, indole was selectively methylated at the C3 position to afford 3-methylindole in 79% yield at the reaction time of 5 h. The ring-methylation of indole using supercritical methanol was claimed to proceed via (1H-indol-3-yl)methanol. The conversion of indole to (1H-indol-3-yl)methanol would be achieved by the electrophilic aromatic substitution between the indol-1-ide (indole anion) and H2C+–OH. The (1H-indol-3-yl)methanol must be reduced to 3-methylindole in the presence of supercritical methanol.  相似文献   

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