Properties of palladium catalysts on carbon supports prepared from chemically modified and activated anthracites

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.     

Graphite powder and multiwalled carbon nanotubes chemically modified with 4-nitrobenzylamine.

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.     

Sorption-spectrometric determination of palladium and gold using silica chemically modified with dipropyl disulfide groups

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.     

PVC-丁二酮肟膜修饰玻碳电极及其在钯的分析中的应用

制备了 PVC-丁二酮肟修饰电极 ,研究了膜电极的响应过程和钯在此电极表面的伏安特性。用微分脉冲伏安法测定 ,钯在 4.76× 1 0 -9mol/ L～ 9.53×1 0 -8mol/ L 的浓度范围内 ,电流与浓度的对数成线性关系 ,检出限为 1 .52×1 0 -9mol/ L。此法可用于矿样中钯的测定。     

Heck reaction catalyzed by a recyclable palladium supported on shell powder

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.     

Self-regeneration of activated carbon modified with palladium catalyst for electrochemical dechlorination

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.     

Protonation of palladium(II)-allyl and palladium(0)-olefin complexes containing 2-pyridyldiphenylphosphine

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.     

Preconcentration procedure trace amounts of palladium using modified multiwalled carbon nanotubes sorbent prior to flame atomic absorption spectrometry: 1st Nano Update

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.     

Stereoselective cyclization using palladium(II) catalyst via hemiacetal intermediates

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.     

聚乙二醇-硫酸铵-二甲酚橙体系萃取分离钯

研究了萃取剂二甲酚橙与Pd(Ⅱ)离子的螯合物在聚合物-硫酸铵-水体系中两相间的分配行为。在pH1．0～6．0条件下，Pd(Ⅱ)几乎被二甲酚橙完全萃取到PEG相中，而Fe(Ⅱ)、Co(Ⅱ)、Zn(Ⅱ)萃取率随pH变化显著，Mn(Ⅱ)、Cd(Ⅱ)基本不被萃取。在HClO4介质pH1．0～2．0条件下，实现了Pd(Ⅱ)与Fe(Ⅱ)、Co(Ⅱ)、Zn(Ⅱ)、Mn(Ⅱ)、Cd(Ⅱ)的定量萃取分离。     

Suzuki-Miyaura cross-coupling of aryl and alkyl halides using palladium/imidazolium salt protocols

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.     

The study of electrochemical palladium behavior using the quartz crystal microbalance

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     

Electrode reactions of palladium(II) in chloride solution at carbon paste electrodes modified with derivatives of N-benzoylthiourea

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 Pd^II 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     

Heck arylations of pent-4-enoates or allylmalonate using a palladium/tetraphosphine catalyst

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.     

Characterization of fossil Sequoioxylon wood using analytical instrumental techniques

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.     

Hydrogenation of aryl ketones using palladium nanoparticles on single-walled carbon nanotubes in an ionic liquid

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.     

木材热塑化

利用适当的化学改性反应特别是经典的纤维索改性反应如酯化、醚化反应对木材进行化学改性，可使木材转化为可熔、可溶的新型热塑性高分子材料。这种热塑性木材可用普通塑料加工成型的方法进行加工，制造出许多新产品。为扩大木材的加工方法、劣废木材资源更有效的综合利用及提高木材的应用价值开辟了新的途径。放已成为近十年来木材综合利用新技术研究开发的新热点之一。本文综述这一研究领域的现状。     

Determination of Cd by electrothermal atomic absorption spectrometry after electrodeposition on a graphite probe modified with palladium

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 (3σ_blank) 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.