共查询到20条相似文献,搜索用时 62 毫秒
1.
B.N. Kuznetsov N.V. Chesnokov N.M. Mikova V.A. Drozdov T.G. Shendrik S.B. Lyubchik I.M. Fonseca 《Reaction Kinetics and Catalysis Letters》2004,83(2):361-367
The influence of chemical modification and thermal activation on the porous structure of Donbass anthracites (Ukraine) and
on the state and catalytic properties of supported palladium has been studied. The most regular distribution of supported
palladium particles with an average size of about 2 nm was observed for the supports prepared from the chemically modified
anthracites. The activity of supported palladium in the liquid-phase hydrogenation of cyclohexene varies more than 10-fold
depending on the preparation method of the anthracite support. The catalysts with the palladium nanoparticles located in micropores
of the carbon support exhibit a lower catalytic activity.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
2.
Gregory G Wildgoose Shelley J Wilkins Gareth R Williams Robert R France David L Carnahan Li Jiang Timothy G J Jones Richard G Compton 《Chemphyschem》2005,6(2):352-362
We demonstrate that graphite powder and multiwalled carbon nanotubes (MWCNTs) can be derivatised by 4-nitrobenzylamine (4-NBA) simply by stirring the graphite powder or MWCNTs in a solution of acetonitrile containing 10 mM 4-NBA. We propose that 4-NBA partially intercalates at localised edge-plane or edge-plane-like defect sites and this hypothesis with a range of experimental data provided by electrochemistry in both aqueous and nonaqueous media, electron microscopy and X-ray powder diffraction. 相似文献
3.
V. N. Losev E. V. Borodina O. V. Buiko N. V. Maznyak A. K. Trofimchuk 《Journal of Analytical Chemistry》2014,69(5):413-419
It has been found that silica chemically modified with dipropyl disulfide groups (DPDSS) quantitatively extracts palladium(II) from solutions in the acidity range from 4 M HCl to pH 4 and gold(III) in the range from 1 M HCl to pH 2 with a partition coefficient at the level of n × 104 cm3/g. The adsorption of palladium(II) and gold(III) at room temperature is highly selective, whereas non-ferrous and other platinum metals are not adsorbed. Sorption-atomic absorption, sorption-ICP-atomic emission, and sorption-photometric methods for the determination of palladium and gold have been developed using DPDSS. The accuracy of the methods was tested by the analysis of certified reference samples. 相似文献
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Yong‐Miao Shen Yi‐Jun Du Min‐Feng Zeng Duo Zhi Sheng‐Xian Zhao Lin‐Mei Rong Shao‐Qin Lv Lin Du Chen‐Ze Qi 《应用有机金属化学》2010,24(9):631-635
A novel palladium catalyst supported on shell powder has been prepared, and its application to the Heck reaction of aryl iodides with olefins has been reported. The results showed that the novel catalyst had extremely high activities for the reactions with the average yield over 90%. Also, this catalyst showed excellent stability in Heck reactions, being reused three times. The catalyst was characterized by X‐ray powder diffraction and field‐emission scanned electron microscopy images, and the energy dispersive X‐ray analyzer. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
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Yan Qing Cong Zu Cheng Wu 《中国化学快报》2007,18(8):1013-1016
Catalyst regeneration and the retention of high catalytic activity are still the critical issues in environmental application.A novel fluidized gas-liquid-solid electrochemical reactor was developed to simultaneously remove chlorinated pollutants and in situ regenerate the spent catalyst.Activated carbon modified with palladium catalyst (AC-Pd) was prepared for electrochemical dechlorination.For the 4-chloropbenol wastewater of initial concentration 200 mg L~(-1),the removal efficiency could nearly reach 100% in less than 30 min.Catalytic activity of AC-Pd catalyst was preserved effectively even in consecutive cycling run without special regeneration.OH radicals,generated by electrochemical reaction,played a critical role in self-regeneration of AC-Pd.High catalytic activity of spent AC-Pd catalyst provided an attractive alternative in wastewater treatment. 相似文献
8.
Daryoush Afzali Rasool Jamshidi Sima Ghaseminezhad Zahra Afzali 《Arabian Journal of Chemistry》2012,5(4):461-466
A method for preconcentration of palladium at trace level on modified multiwalled carbon nanotubes columns and determination by flame atomic absorption spectrometry (FAAS) has been developed. Multiwalled carbon nanotubes (MWCNTs) were oxidized with concentrated HNO3 and the oxidized multiwalled carbon nanotubes were modified with 5-(4′-dimethylamino benzyliden)-rhodanine, and then were used as a solid sorbent for preconcentration of Pd(II) ions. Factors influencing sorption and desorption of Pd(II) ions were investigated. The sorption of Pd(II) ions was quantitative in the pH range of 1.0–4.5, whereas quantitative desorption occurs with 3.0 mL 0.4 mol L?1 thiourea. The amount of eluted palladium was measured using flame atomic absorption spectrometry. The effects of experimental parameters, including sample flow rate, eluent flow rate, and eluent concentration were investigated. The effect of coexisting ions showed no interference from most ions tested. The proposed method permitted a large enrichment factor (about 200). The relative standard deviation of the method was ±2.73% (for eight replicate determination of 2.0 μg mL?1 of Pd(II)) and the limit of detection was 0.3 ng mL?1. The method was applied to the determination of Pd(II) in water, road dust, and standard samples. 相似文献
9.
The pendant nitrogen atom of the Ph2PPy ligand in the Pd(II)-allyl complexes [PdCl(η3-2-CH3-C3H4)(Ph2PPy)] (1) and [Pd(η3-2-CH3-C3H4)(Ph2PPy)2]BF4 (3) has been protonated with methanesulfonic acid to afford the corresponding pyridinium salts [PdCl(η3-2-CH3-C3H4)(Ph2PPyH)](CH3SO3) (1a) and [Pd(η3-2-CH3-C3H4)(Ph2PPyH)2](CH3SO3)2(BF4) (3a).Protonation strongly influences the 1H and 13C NMR spectral parameters of the allyl moieties of 1a and 3a whose signals resonate at lower fields with respect to the parent species indicating that upon protonation Ph2PPy becomes a weaker σ-donor and a stronger Π-acceptor. The allyl moiety, which in 1 is static, becomes dynamic in 1a, the observed syn-syn and anti-anti exchange being due to deligation of the protonated phosphine from the metal centre. Treatment of complex 3 with diethylamine in the presence of fumaronitrile gives the new Pd(0)-olefin complex [Pd(η2-fumaronitrile)(PPh2Py)2] (4) which has been characterized by elemental analysis and NMR spectroscopy. Low temperature protonation of 4 with methanesulfonic acid leads to the bis-protonated species [Pd(η2-fumaronitrile)(Ph2PPyH)2](CH3SO3)2 (4a) which is stable only at temperatures <0 °C. 相似文献
10.
Masahiro Miyazawa 《Tetrahedron letters》2004,45(14):2883-2886
A stereoselective palladium-catalyzed cyclization of 3-phenyl-7-hydroxy-5-heptenal was developed. The reaction was carried out to give 2,4,6-trisubstituted tetrahydropyran with highly controlled 4,6-cis stereochemistry. 相似文献
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Michał Grdeń Jan Kotowski Andrzej Czerwiński 《Journal of Solid State Electrochemistry》2000,4(5):273-278
The electrochemical quartz crystal microbalance (EQCMB) method has been used to evaluate the processes which occur in/on
the palladium electrode in basic solutions. Hydrogen electrosorption in palladium is accompanied by an additional frequency
shift that can be attributed to the stresses generated inside the Pd metal. A non-linear dependence between the mass change
and the charge consumed during hydrogen oxidation in the Pd electrode has been found for hydrogen absorbed in the α- and β-phases.
This effect precludes the objective estimation of the amount of hydrogen absorbed inside the Pd electrode. The EQCMB method
has been used, however, for studying the surface electrode processes on the Pd electrode, i.e. specific anion adsorption,
surface oxidation and dissolution. Also, the structure of the palladium oxide formed on the Pd surface during electrochemical
oxidation is discussed in this paper and the effect of the anodic limiting potential on the oxide structure is reported.
Received: 10 August 1999 / Accepted: 24 September 1999 相似文献
13.
Karl-Heinz Lubert Markus Guttmann Lothar Beyer 《Journal of Solid State Electrochemistry》2002,6(8):545-552
The study of the electrode reactions of palladium(II) at non-modified carbon paste electrodes (CPEs) in chloride solution
has revealed the existence of a chloropalladate(II) complex at the electrode surface. The complex is formed during the application
of anodic potentials after preceding palladium deposition. In the present paper the electrode reactions of PdII at CPEs modified with some N′,N′-disubstituted derivatives of N-benzoylthiourea [as selective ligands for palladium(II)] are studied in chloride solution by cyclic voltammetry. Two reduction
peaks are observed in the cathodic scans recorded after deposition of palladium and anodization of the electrode. From the
results it is concluded that [in addition to the chloropalladate(II) complex, observed at the non-modified electrode] a second
palladium complex is formed at positive potentials. The formation of the palladium(II) complex of the N-benzoylthiourea derivatives by ligand exchange at the electrode surface is assumed. The ligand exchange itself occurs without
charge transfer across the electrode|solution interface; therefore, it cannot be detected electrochemically. After palladium
deposition and anodic treatment a pronounced "inverse" peak (i.e., an anodic peak in the cathodic scan) with peak currents
up to 100 μA is observed at about +0.8 V. Its peak current increases with the amount of deposited palladium and the number
of cycles. The reactions at the electrode surface are discussed. The results of the study reveal the existence of two different
surface complexes of palladium(II) at ligand-modified CPEs, but the surface reactions could not be elucidated in detail.
Electronic Publication 相似文献
14.
A simple new protocol for the high yielding Suzuki-Miyaura cross-couplings of aryl chlorides with aryl boronic acids using a palladium/imidazolium salt catalytic system is presented. The first examples of a palladium/imidazolium salt protocol for sp3-sp3 Suzuki-Miyaura couplings of alkyl halides are also disclosed. 相似文献
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Mhamed Lemhadri Touriya Zair Maurice Santelli 《Journal of organometallic chemistry》2007,692(11):2270-2281
The Heck reaction of aryl halides with functionalised alk-1-enes should be a powerful method for the synthesis of functionalised (E)-1-arylalk-1-ene derivatives. The major problem of this reaction is the palladium-catalysed migration of the carbon-carbon double bond along the alkyl chain when there are no substituents on the C3 carbon of the alk-1-enes. We observed that for the arylation of ethyl pent-4-enoate, ethyl 2-methylpent-4-enoate or dimethyl allylmalonate this migration could be partially or completely controlled using appropriate reaction conditions. The ramification on the alkyl chain and the substituents on the aryl halide have also an important influence on this migration. Moreover, the cis,cis,cis-1,2,3,4-tetrakis(diphenylphosphinomethyl)cyclopentane/1/2[PdCl(C3H5)]2 system catalyses this reaction with a wide range of aryl bromides using very high ratio substrate/catalyst in good yields. 相似文献
17.
Traces of Cd were determined by electrothermal atomic absorption spectrometry after electrochemical preconcentration on a commercial graphite ridge probe modified with Pd. The Pd electrochemically deposited on the probe surface served not only as the modifier but it also protected the graphite surface. Cd was electrodeposited at a controlled potential − 1.2 V (vs. saturated calomel electrode) using the Pd-modified graphite probe as a working electrode. The sensitivity of Cd determination remained unchanged for 300 electrodeposition and atomization cycles. The detection limit (3σblank) was improved with increasing time of electrolysis and was 1.2 ng l− 1 for a 10 min electrolysis time in the presence of 0.1 mol l− 1 NaNO3. The procedure was applied for the determination of Cd in (1 + 1) diluted seawater and in (1 + 1) diluted urine samples using the standard addition method. 相似文献
18.
Single-walled carbon nanotubes (SWNTs) are used as supporting materials for palladium (Pd) nanoparticles generated in situ in ionic liquid (IL); Pd nanocatalysts on SWNTs exhibit superior reactivity for hydrogenation of aryl ketones in IL under mild conditions (1 atm of H2 (g) and room temperature) and can be reused above 10 times without any loss of catalytic activity. 相似文献
19.
In this study, fossil (Sequoioxylon) wood from the Oligocene–Miocene transition in İstanbul, Turkey was examined using non-destructive test methods to evaluate changes in anatomical and chemical structure. Molecular changes in the cell wall structure of the wood were determined using Fourier transform infrared (FTIR) and FT-Raman spectroscopy, along with the comparison to recent wood [Sequoiadendron giganteum (Lindl.)]. We found that the cell wall carbohydrates of the fossil wood were significantly more degraded compared with lignin; FT-Raman spectroscopy revealed the degradation in more detail compared with FTIR spectroscopy. FT-Raman spectra also demonstrated that hemicellulose and holocellulose were decreased in the fossil wood. Laser-induced breakdown spectroscopy (LIBS) analysis confirmed that the mass loss was due to the decreased H and O content of the fossil wood sample and was caused by decomposition. Light microscopy also showed that fossil and recent woods have similar anatomic structures, and that the micro-morphological structure of the fossil wood was well-preserved. 相似文献
20.
The binding of palladium to high-molecular-mass compounds in palladium-treated lettuce is investigated as an example for a biological matrix. The total palladium concentration in lettuce leaves is 10.3 ng/g wet weight. After homogenization, high-molecular-mass compounds (> 10 kDa) are isolated by ultrafiltration. For separation of these palladium species a combination of preparative gel permeation chromatography (GPC) and preparative isotachophoresis (ITP) is used. Palladium is determined in separated fractions by using a highly sensitive total reflection X-ray fluorescence (TXRF) method after preconcentration. After GPC separation, four main fractions of palladium species are collected, each containing palladium in ng quantities (3-10 ng). Two of these fractions are further separated by ITP, yielding at least three main peaks per GPC fraction, each containing palladium in the range of 0.3-3 ng. These palladium containing peaks are characterized by high-performance size exclusion chromatography (HPSEC) and capillary isotachophoresis (cITP) in parallel. HPSEC enables the estimation of the molecular mass of six main palladium peaks, covering a molecular mass range of 69-200 kDa. It is also shown that the estimation of molecular mass after separation is more reliable than the respective estimation directly in the first GPC run. However, cITP reveals that each of the separated peaks is still a mixture of at least five different compounds. 相似文献