Nature of the modifying action of white phosphorus on the properties of nanosized hydrogenation catalysts based on bis(dibenzylideneacetone)palladium(0)

The catalytic properties and nature of the nanoparticles forming in the system based on Pd(dba)₂ and white phosphorus are reported. A schematic mechanism is suggested for the formation of nanosized palladium-based hydrogenation catalysts. The mechanism includes the formation of palladium nanoclusters via the interaction of Pd(dba)₂ with the solvent (N,N-dimethylformamide) and substrate and the formation of palladium phosphide nanoparticles. The inhibiting effect exerted by elemental phosphorus on the catalytic process is due to the conversion of part of the Pd(0) into palladium phosphides, which are inactive in hydrogenation under mild conditions, and the formation of mainly segregated palladium nanoclusters and palladium phosphide nanoparticles. By investigating the interaction between Pd(dba)₂ and white phosphorus in benzene, it has been established that the formation of palladium phosphides under mild conditions consists of the following consecutive steps: Pd(0) → PdP₂ → Pd₅P₂ → Pd₃P. It is explained why white phosphorus can produce diametrically opposite effects of on the catalytic properties of nanosized palladium-based hydrogenation catalysts, depending on the nature of the palladium precursor.     

Deep Oxidation of Methane on a Pt/Si3N4 Catalyst

We have studied platinum catalysts supported on silicon nitride Si₃N₄ in the process of deep oxidation of methane. We have used transmission electron microscopy and X-ray photoelectron spectroscopy to study the surface properties of the Pt/Si₃N₄ samples before and after the catalytic reaction. We have established that the metallic platinum particles in freshly prepared systems are characterized by average sizes of 1.7-5.3 nm, while after the catalytic reaction we observe formation of Pt crystallites up to 30-70 nm in size. We hypothesize that the observed deactivation of platinum catalysts in deep oxidation of methane is connected with crystallization of the metallic particles and their entrainment with the reaction products during catalysis.     

Effect of preparation conditions on the formation of the active phase of carbon fiber catalytic systems for the low-temperature oxidation of carbon monoxide

We studied the effects of the composition of impregnating solution and heat treatment conditions on the activity of catalytic systems for the low-temperature oxidation of CO obtained by the impregnation of Busofit carbon-fiber cloth with aqueous solutions of palladium, copper, and iron salts. The formation of an active phase in the synthesized catalysts at different stages of their preparation was examined with the use of differential thermal and thermogravimetric analyses, X-ray diffraction analysis, X-ray photoelectron spectroscopy, and elemental spectral analysis. The catalytic system prepared by the impregnation of electrochemically treated Busofit with the solutions of PdCl₂, FeCl₃, CuBr₂, and Cu(NO₃)₂ and activated under optimum conditions ensured 100% CO conversion under a respiratory regime at both low (0.03%) and high (0.5%) carbon monoxide contents of air. It was found that the activation of a catalytic system at elevated temperatures (170–180°C) leads to the conversion of Pd(II) into Pd(I), which was predominantly localized in a near-surface layer. The promoting action of copper nitrate consists in the formation of a crystalline phase of the rhombic atacamite Cu₂Cl(OH)₃. The catalyst surface is finally formed under the conditions of a catalytic reaction, when a joint Pd(I)-Cu(I) active site is formed.     

Influence of Pd precursors on the catalytic performance of Pd–H4SiW12O40/SiO2 in the direct oxidation of ethylene to acetic acid

The effects of palladium precursors (PdCl₂, (NH₄)₂PdCl₄, Pd(NH₃)₂Cl₂, Pd(NO₃)₂ and Pd(CH₃COO)₂) on the catalytic properties in the selective oxidation of ethylene to acetic acid have been investigated for 1.0 wt% Pd–30 wt% H₄SiW₁₂O₄₀/SiO₂. The structures of the catalysts were characterized using X-ray diffraction, N₂ adsorption, H₂-pulse chemical adsorption, infrared spectrometry of the adsorbed pyridine, H₂ temperature-programmed reduction and X-ray photoelectron spectroscopy. The present study demonstrates that the different palladium precursors can lead to the significant changes in the dispersion of palladium. It is found that Pd dispersion decreases as follows: PdCl₂ > (NH₄)₂PdCl₄ > Pd(NO₃)₂ > Pd(NH₃)₂Cl₂ > Pd(C₂H₃O₂)₂, which is nearly identical to the catalytic activity. This indicates that the dispersion of palladium plays an important role in the catalytic activity. Furthermore, density of Lewis (L) and Brönsted (B) acid sites are also strongly dependent on the palladium precursors. It is also demonstrated that an effective catalyst should possess a well combination of Brönsted acid sites with dispersion of palladium.     

Formation and the nature of activity of Ziegler systems based on palladium β-diketonate complexes in hydrogenation catalysis

The catalytic properties and nature of Ziegler-type Pd(Acac)₂ and Pd(Acac)₂PPh₃ based catalysts are studied in the hydrogenation of unsaturated compounds. The causes of an extremum appearing in the dependence of the specific activity of the catalyst in styrene and phenylacetylene hydrogenation on the proportions of the starting components are considered. The increase in the specific activity of the Pd(Acac)₂ + AlEt₃ catalytic system in hydrogenation as a function of the Al/Pd ratio arises from an increase in the degree of dispersion of the microheterogeneous system, an increase in the fraction of reduced palladium, and changes in the nature of the ligand shell. The inhibiting effect is caused by triethylaluminum adsorption on palladium nanoparticles. Palladium nanoparticle models are suggested.     

Combustion of methane over supported palladium-copper bimetallic catalysts

Monometallic and bimetallic catalysts based on palladium and copper deposited on a spinel carrier have been investigated in the catalytic combustion of methane. Great differences were found in catalytic activity, according to the sequence Pd/MgAl₂O₄>CuO–Pd/MgAl₂O₄>Pd–CuO/MgAl₂O₄>CuO/MgAl₂O₄. They were explained by changes in surface composition of the catalysts. In the case of bimetallic catalysts the metallic surface is preferentially enriched in copper, which acts as a diluting agent for the Pd atom ensembles. As a consequence, the adsorption of reactants is limited and the catalysts so obtained behave like copper slightly doped with palladium.     

Catalytic Active Site for NO Decomposition Elucidated by Surface Science and Real Catalyst

Comprehensive studies combining surface science and real catalyst were performed to get further insight into catalytic active site and reaction mechanism for NO decomposition over supported palladium and cobalt oxide-based catalysts. On palladium single-crystal model catalysts, adsorption, dissociation and desorption behavior of NO was found to be closely related to the surface structures, the stepped surface palladium being active for dissociation of NO. In accordance with this result, the activity of powder Pd/Al₂O₃ catalysts for NO decomposition was directly related to the number of step sites exposed on the surface, suggesting that the step sites act as the catalytic active site for NO decomposition on Pd/Al₂O₃. NO decomposition over cobalt oxide was found to be significantly promoted by addition of alkali metals. Surface science study and catalyst characterization led to the same conclusion that the interface between the alkali metal and Co₃O₄ serves as the catalytic active site. From the results of in situ Fourier transform infrared (FT-IR) spectroscopy and isotopic transient kinetic analysis, a reaction mechanism was proposed in which the reaction is initiated by NO adsorption onto alkali metals to form NO₂⁻ species and then NO₂⁻ species react with the adsorbed NO species to form N₂ over the interface between the alkali metal and Co₃O₄.     

Heterogenization of palladium(II) chelates on a sibunite

Summary Heterogenized palladium(II) chelates have been prepared by a sibunite treatment of acetone or aqueous solutions of palladium complexes with alizarin red C, 4- anilino-pent-3-en-2-one,N, N-bis(acetylacetone)ethylenediamine, 1-phenyl-4-methylpent-4-en-1,3-dione and 1-phenyl-3-anilino-4-methylpent-4-en-1-one. The catalytic properties of these chelates in chloronitrobenzene hydrogenation have been studied. It was found that the catalytic activity approaches 159 mol H₂ (mol Pd min)^–1 depending on the chlorine atom position in the aromatic ring and the nature of the solvent. The catalysts do not lose their activity after five cycles. The products of chloronitrobenzene hydrogenation are chloroanilines (up to 90%), azo- and azoxychlorobenzenes (5–7%) as a result of incomplete reduction as well as small quantities (2–5%) of dehalogenated azo-, azoxybenzenes and aniline.     

Synthesis,Characterization, and Catalysis of Water-Soluble Trimeric and Monomeric Palladium Complexes of 8-Aminoquinolines

New water soluble neutral and cationic palladium complexes were synthesized using 8-aminoquinoline (8-AQ) and 2-methyl 8-aminoquinoline (2-Me 8-AQ) ligands and their catalytic properties were evaluated. The neutral trimeric complexes having a Pd₃N₃ core were found to form when Pd(OAc)₂ was reacted with 8-AQ or 2-Me 8-AQ irrespective of the stoichiometry between the 2 reagents. Controlled addition of triflic acid to the neutral trimeric complex resulted in the formation of a trimeric cationic palladium complex as well as a monomeric cationic complex. A cationic palladium complex having two units of 2-Me-8AQ ligand was also synthesized from the cationic monomeric complex. Crystal structures of the new palladium complexes are reported in this study. The water-soluble neutral palladium complex showed catalytic activity for the oxidation of benzyl alcohols to benzaldehydes, while the cationic palladium complexes were found to be efficient catalysts for the oxidation of styrenes to methyl ketones.     

硅纳米片负载钯催化剂的制备及其催化Suzuki反应研究

通过硅化钙在酸性条件下水解制得二维硅纳米片载体材料,经3-氨丙基三乙氧基硅烷化学改性后与钯配位,再经还原得到了一种新型的硅纳米片负载钯催化剂,采用透射电镜和电感耦合等离子体质谱(ICP-MS)等手段对其进行了表征.并将该催化剂成功应用于Suzuki反应,结果表明,硅纳米片负载钯催化剂在较低的钯催化量和空气氛围下即可有效地催化多种溴代芳烃和芳基硼酸的Suzuki偶联反应.此外,该催化剂经8次循环使用后,催化活性无明显下降.     

Untersuchungen an Metallkatalysatoren. XVII. Phasenaufbau,Dispersität und Dehydrieraktivität Molybdän- und wolframmodifizierter Palladiumkatalysatoren

Investigations on Metal Catalysts. XVII. Phase Structure, Dispersity, and Dehydrogenation Activity of Palladium Catalysts Modifided by Molybdenum and Tungsten Molybdenum and tungsten containing palladium catalysts were prepared by reduction of mixtures from Pd(NO₃)₂ with MoO₃ and WO₃, respectively, with hydrogen at 600°C and 800°C. The powders were characterized by means of several methods: Determination of the oxidation state for molybdenum and tungsten, X-ray measurements, N₂ adsorption, CO chemisorption, H₂ sorption, dehydrogenation of cyclohexane. The properties of the samples (heated at 600°C) are determined to a high degree by the co-existence of the palladium phase as well as the molybdenum and tungsten oxide, respectively, in the mean oxidation state +4. The after-reduction at 800°C leads to a great portion of metallic molybdenum and tungsten in the concerned catalysts. There are references that the treatment at 800°C in the presence of hydrogen causes for the Pd? Mo catalysts an increase of the palladium content in the surface of the crystallites.     

Influence of CeO2 addition on the physicochemical and catalytic properties of Pd/TiO2 catalysts in CO oxidation

The influence of CeO₂ addition on the formation of the microstructure, electronic state, and catalytic properties of Pd/TiO₂ supported catalysts in CO oxidation were investigated. It was shown that, when Pd is supported on titanium dioxide modified with cerium dioxide, annealing at 500°C results in the formation of Pd/(CeO₂-TiO₂) catalysts with a nanocrystalline structure composed of incoherently intergrown fine anatase crystals and interblock boundaries in which palladium and cerium are stabilized. The higher catalytic activity of Pd/(CeO₂-TiO₂) catalysts compared to Pd/TiO₂ catalysts is explained by the smaller size of Pd particles and the higher proportion of palladium in the Pd^δ+ state.     

Impact of palladium silicide formation on the catalytic properties of Pd/SiO2 catalysts in liquid-phase semihydrogenation of phenylacetylene

In this study, palladium silicide was formed on the sol–gel derived SiO₂ supported Pd catalysts when they were prepared by ion-exchange method using Pd(NH₃)₄Cl₂ as a palladium precursor. No other palladium phases (PdO or Pd⁰) were evident after calcinations at 450 °C for 3 h. The Pd/SiO₂ catalysts with Pd silicide formation were found to exhibit superior performance than commercial SiO₂ supported ones in liquid-phase semihydrogenation of phenylacetylene. From XPS results, the binding energy of Pd 3d of palladium silicide on the Pd/SiO₂ catalyst shifted toward larger binging energy, indicating that Pd is electron deficient. This could probably result in an inhibition of a product styrene on the Pd surface and hence high styrene selectivities were obtained at high phenylacetylene conversions. The formation of Pd silicide, however, did not have much impact on specific activity of the Pd catalysts since the TOFs were quite similar among the various catalysts with or without palladium silicides if their average particle sizes were large enough. The TOFs decreased by an order of magnitude when palladium dispersion was very high and their average particle sizes were smaller than 3–5 nm.     

Influence of chelate ring size on the properties of phosphine-sulfonate palladium catalysts

Phosphine-sulfonate based palladium is one of the most extensively studied catalyst systems in olefin polymerization.This type of catalyst features six-membered chelate ring size,and can enable the copolymerizations of ethylene with a wide variety of polar monomers.In this contribution,we decide to investigate the influence of chelate ring size on the properties of phosphinesulfonate palladium catalysts.As such,a series of phosphine-sulfonate ligands and the corresponding seven-membered ring Pd(II)complexes[κ~2-(P,O)-2-(CH_2-PR_1R_2)-4-methylphenyl-sulfonato]Pd(Me)(DMSO)(Pd1,R_1=R_2=Cy,Pd2,R_1=R_2=o-Me O-C_6H_4;Pd3,R_1=Ph,R_2=2-[2,6-(Me O)_2C_6H_3]C_6H_4;DMSO=dimethyl sulfoxide)were designed,prepared and characterized.These palladium complexes are moderately active when they were applied in ethylene polymerization and copolymerizations with methyl acrylate and butyl vinyl ether.However,their properties are greatly reduced from those of the classic six-membered ring phosphine-sulfonate palladium complex Pd2′.The experimental results indicate that the bigger chelate ring size can increase the ligand flexibility and damage the catalytic properties for the phosphine-sulfonate type palladium catalysts.     

Pd/γ-Al2O3催化剂对烟气中多环芳烃的氧化性能研究

实验采用等体积浸渍法制备了系列Pd/γ-Al2O3催化剂.采用模拟实验装置并结合XRD、N2吸/脱附、TEM、H2 -TPR和SEM-MAPS等手段对催化剂的组成及结构进行了表征,系统地考察了各催化剂对燃煤烟气中PAHs的催化氧化性能.结果表明,催化剂对烟气中PAHs排放总量的氧化效率为67.3％～93.5％,且烟气中...     

Palladium(II)‐N‐heterocyclic carbene complexes: synthesis,characterization and catalytic application

N‐Heterocyclic carbenes (NHCs) are of great importance and are powerful ligands for transition metals. A new series of sterically hindered benzimidazole‐based NHC ligands (LHX) ( 2a , 2b , 2c , 2d , 2e , 2f ), silver–NHC complexes ( 3a , 3b , 3c , 3d , 3e , 3f ) and palladium–NHC complexes ( 4a , 4b , 4c , 4d , 4e , 4f ) have been synthesized and characterized using appropriate spectroscopic techniques. Studies have focused on the development of a more efficient catalytic system for the Suzuki coupling reaction of aryl chlorides. Catalytic performance of Pd–NHC complexes and in situ prepared Pd(OAc)₂/LHX catalysts has been investigated for the Suzuki cross‐coupling reaction under mild reaction conditions in aqueous N,N‐dimethylformamide (DMF). These complexes smoothly catalyzed the Suzuki–Miyaura reactions of electron‐rich and electron‐poor aryl chlorides. Copyright © 2014 John Wiley & Sons, Ltd.     

Catalytic Oxidation of Small Molecules in a Gas Phase in the Presence of Heterogenized Platinum and Palladium Complexes with Chemically Different Ligands

This work is devoted to the study of catalytic properties of the metal complexes of platinum and palladium with acetylacetone and N-allyl-N"-propylthiourea heterogenized on the surface of silica in the oxidation reactions of H₂ and CO in a gas phase. We found that the acetylacetonate complexes were not degraded under catalytic reaction conditions, whereas the metal complexes withN-allyl-N"-propylthiourea exhibited a high activity only after partial degradation of the ligand. We demonstrated that the catalytic activity of the grafted metal complexes was higher than that of traditional supported platinum and palladium catalysts with the same metal content. Taking into account the structure of active centers in Pt and Pd complexes grafted on SiO₂ and the interaction of these centers with reactants, we proposed a detailed mechanism for the catalytic action, which adequately describes the entire set of experimental data.     

Hydrogenation of aromatic hydrocarbons in a mixture with thiophene on sulfided Pd/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts

The activity and stability of aluminum-palladium catalysts in the hydrogenation of aromatic hydrocarbons mixed with thiophene were studied. The catalysts were obtained by impregnation of γ-A₂O₃ with aqueous solutions of salts of palladium complexes. Preliminary sulfiding followed by oxidative activation of Pd/Al₂O₃ catalysts were found to favor the formation of such palladium state on the surface at which the hydrogenation of aromatic hydrocarbons in the presence of sulfur-containing impurities proceeds without a noticeable change in the activity with time. IR spectroscopy showed that the palladium metal surface fragments forming CO complexes with a characteristic absorption band at 1998 cm^–1 are resistant to poisoning with sulfur-containing compounds in the hydrogenation of aromatic hydrocarbons.     

Palladium catalyzed three component coupling reaction between chromones, alcohols, and allylic acetates: diversity-oriented synthesis of highly substituted chromones

This paper describes the palladium catalyzed highly efficient three component coupling (TCC) reactions between chromones, allylic acetates, and alcohols, which lead to a library of multiply substituted chromones. The activity of various palladium catalysts, such as Pd(PPh₃)₄ and Pd₂dba₃·CHCl₃ and their combination with various bisphosphine ligands, was investigated by using THF as a solvent, which revealed that Pd(PPh₃)₄ catalyst was the best one. The reaction most probably proceeds via the formation of benzopyrilium cation, generated from the reaction between chromones and allyl acetate, in the presence of palladium catalyst. The subsequent trapping of the benzopyrilium cation by alcohols would give the corresponding products in excellent yields. This alkoxy-allylation reaction was highly diastereoselective and only one diastereomer was obtained in all the cases.     

Factors determining the chemoselectivity of phosphorus-modified palladium catalysts in the hydrogenation of chloronitrobenzenes

The precursor nature effect on the state of the Pd–P surface layer in palladium catalysts and on their properties in the liquid-phase hydrogenation of chloronitrobenzenes under mild conditions has been investigated. A general feature of the Pd–P-containing nanoparticles obtained from different precursors and white phosphorus at P/Pd = 0.3 (PdCl₂ precursor) and 0.7 (Pd(acac)₂ precursor) is that their surface contains palladium in phosphide form (BE(Pd3d _5/2) = 336.2 eV and BE(Р2р) = 128.9 eV) and Pd(0) clusters (BE(Pd3d_5/2) = 335.7 eV). Factors having an effect on the chemoselectivity of the palladium catalysts in chloronitrobenzenes hydrogenation are considered, including the formation of small palladium clusters responsible for hydrogenation under mild conditions.