Palladium magnetic nanoparticle‐polyethersulfone composite membrane as an efficient and versatile catalytic membrane reactor

Developing polymer catalytic membrane reactors is an aim due to its outstanding advantages. In this paper, a novel catalytic membrane containing palladium‐supported magnetic nanoparticles is introduced. Silica‐iron oxide core shell nanoparticles were first prepared and functionalized by phosphine ionic liquid functionalized poly(ethylene glycol). The modified magnetic nanoparticles were used as support for immobilization of palladium. The final palladium‐immobilized nanoparticles were used as active filler for the preparation of membrane reactor. The prepared membranes were characterized, and their activities were tested in carbon‐carbon bond formation and catalytic reduction. The catalytic membrane showed good performance in the mentioned reactions.     

Palladium nanoparticles in aqueous solution: Preparation,properties, and effect of their size on catalytic activity

A method has been developed for the preparation of palladium nanoparticles with different sizes of up to 7 nm via the reduction of Pd(II) ions with hydrogen in an aqueous solution on seed metal nanoparticles (2.5 nm). The effect of the size of nanoparticles on their catalytic activity in methyl viologen reduction with molecular hydrogen in an alkaline medium has been studied. It has been found that the specific catalytic activity of palladium nanoparticles is independent of their size.     

Structure and catalytic properties of nanosized alumina supported platinum and palladium particles synthesized by reaction in microemulsion

Mixtures of nanosized platinum and palladium particles have been prepared by reduction of salt-containing microemulsion droplets using hydrazine as the reducing agent. To avoid possible negative effects of the presence of sulfur compounds during the preparation the microemulsion was made using the sulfur-free nonionic polyoxyethylene 4 lauryl ether surfactant. Transmission electron microscopy showed that the as-prepared mixtures contained crystalline platinum particles of fairly homogeneous size (20 to 40 nm) with adsorbed amorphous palladium particles 2 to 5 nm in size. Catalyst samples were prepared by depositing the nanoparticles on a gamma-Al(2)O(3) support followed by heating in air at 600 degrees C. Alloyed particles of platinum and palladium with sizes ranging from 5 to 80 nm were obtained during the heating. The majority of the particles had the fcc structure and their compositional range was dependent upon the Pt:Pd molar ratio of the microemulsion. A catalyst prepared from a microemulsion with a 20:80 Pt:Pd molar ratio showed the highest catalytic activity for CO oxidation, while pure platinum and palladium catalysts showed higher sulfur resistance. These results differ from the performance of conventional wet-impregnated catalysts, where a 50:50 Pt:Pd molar ratio resulted in the highest catalytic activity as well as the highest sulfur resistance.     

透氢钯复合膜的原理、制备及表征

钯及其合金膜由于具有透氢性好和耐高温的特点,除了用作氢气分离和纯化器外,还可以用作脱氢、制氢等反应的反应器,以实现反应和分离的一体化,并提高转化率和选择性。本文综述了钯基复合膜的原理、制备及表征,并重点介绍了本研究组的光催化镀膜工艺。     

透氢钯复合膜的原理、制备及表征

钯及其合金膜由于具有透氢性好和耐高温的特点,除了用作氢气分离和纯化器外,还可以用作脱氢、制氢等反应的反应器,以实现反应和分离的一体化,并提高转化率和选择性。本文综述了钯基复合膜的原理、制备及表征,并重点介绍了本研究组的光催化镀膜工艺。     

Nano-scale effects in electrochemistry

We report combined scanning tunneling microscopy and electrochemical reactivity measurements on individual palladium nanoparticles supported on a gold surface. It is shown that the catalytic activity towards electrochemical proton reduction is enhanced by more than two orders of magnitude as the diameter of the palladium particles parallel to the support surface decreases from 200 to 6 nm. Density functional theory (DFT) calculations combined with molecular dynamics (MD) simulations have been used to investigate the origin of the effect. It is concluded that the size effect is given by the thickness-variation of the support-induced strain at the surface of the palladium nanoparticles.     

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.     

Self-sustained oscillations within the temperature hysteresis in CO oxidation over Pd: Mathematical model of a cascade of continuous stirred-tank reactors

The results of temperature-programmed reaction experimental studies and mathematical modeling of self-sustained oscillations within an inverse temperature hysteresis in CO oxidation over Pd catalyst are presented. The experimental data demonstrate the influence of the reaction medium on the catalyst activity under reaction conditions. Under oxygen excess in the feeding gas mixture and high temperature, the defects appeared on the initially flat surface of metallic palladium due to deep oxidation of palladium (three-dimensional PdO nanoparticles were observed). The palladium oxide reduced under cooling of the catalytic system, and the catalyst surface became flat again. To take into account these variations of the palladium surface structure, we consider the piecewise-constant dependence of the rate constant of some reaction step on the concentrations of oxygen species, namely, the dissolved oxygen or oxide in the palladium bulk. The proposed model of the process in the cascade of continuous stirred-tank reactors that account for these dependences qualitatively describes the inverse temperature hysteresis as well as the oscillatory dynamics within the hysteresis loop which were obtained experimentally.     

Oxygen reduction at platinum monolayer islands deposited on Au(111)

Atomic monolayer islands of Pt, namely, two-dimensional Pt nanoparticles, on a Au(111) electrode have been studied for the first time, focusing on their electrocatalytic activities for oxygen reduction in acid solutions. The Pt islands' electrodes were prepared using the self-assembled technique of thiols together with the replacement of Pt with a Cu monolayer. The states of adsorbed OH and the catalytic activities of oxygen reduction were sensitive to the Pt island size. As island size decreased, a delay in the reduction of surface oxide was observed. However, negligible influence of adsorbed OH on activity for oxygen reduction was observed. Pt islands of sizes ranging from 5 to 10 nm showed higher specific catalytic activities for oxygen reduction. Specific catalytic activities decreased by a factor of 10 with a decrease in island sizes from 5.5 to 3.1 nm. Size effects observed in Pt monolayer islands were discussed in comparison with three-dimensional nanoparticles, to obtain information concerning the size effects of metal nanoparticles.     

Chelated palladium nanoparticles on the surface of plasma‐treated polyethersulfone membrane for an efficient catalytic reduction of p‐nitrophenol

Herein, a novel method was reported for the use of polyethersulfone (PES) membranes in catalytic reactions with an enhanced distribution and superior catalytic activity of palladium nanoparticles immobilized on the surface of the membranes. For this purpose, the surface of PES membrane was treated with plasma, and subsequently, the consequent oxygen‐containing functional groups were reacted with APTES and 2‐pyridinecarbaldehyde, respectively, to provide sites by which Pd could form complexes. The mean roughness as well as the surface and cross‐sectional morphology were investigated using atomic force microscopy, scanning electron microscopy (SEM), and field‐emission scanning electron microscopy (FESEM), respectively. Furthermore, SEM mapping was used to examine the palladium distribution on the surface of the membranes. Further characterizations of as‐prepared Pd‐loaded PES membranes conducted using EDX, ICP, and XRD analyses. The reduction of p‐nitrophenol to p‐aminophenol was also used as a model reaction to investigate the membranes' performance. The results, analyzed using UV‐Vis instrument, demonstrated that the complete reduction of p‐nitrophenol was achieved at a short time via Pd‐chelated plasma‐treated membrane. Furthermore, the rod‐like and sphere‐like structure of Pd was acquired as a result of palladium chelating with nitrogen‐containing ligands, produced through the reaction between 2‐pyridinecarbaldehyde and (3‐Aminopropyl)triethoxysilane. It was observed that the rod‐like structure of Pd exhibited a trivial catalytic activity in reduction of p‐nitrophenol to p‐aminophenol in contrast with the sphere‐like structure, nonetheless.     

Copper sols stabilized by poly(ethylene glycol-600-monolaurate) and its complexes with poly(acrylic acid)

Copper sols stabilized by a polymer-colloid complex are studied via dynamic light scattering and transmission electron microscopy. It is shown that the polymer-colloid complex including poly(acrylic acid) and the nonionogenic polymeric surfactant poly(ethylene glycol-600-monolaurate) is an effective protector of copper nanoparticles formed via the reduction of Cu²⁺ ions in an aqueous medium. The sizes of sol particles of the nanocomposite consisting of the polymer-colloid complex and copper nanoparticles depend on the method of preparation of the nanocomposite. The incorporation of the copper nanoparticles being formed (an average diameter of 5 nm) into particles of the polymer-colloid complex leads to an insignificant change in the sizes of the complex particles. The same sizes are typical for particles of the nanocomposite formed during the introduction of surfactant micelles in the copper sol formed in the solution of poly(acrylic acid). The interaction of copper nanoparticles formed in an aqueous medium with surfactant micelles entails their aggregation; as a result, these nanoparticles turn out to be incorporated into large aggregates with equivalent radii of up to 100 nm. When poly(acrylic acid) is incorporated into this sol, the sizes of its particles insignificantly change apparently because of the low rate of structural rearrangements accompanying the formation of the polymer-colloid complex.     

The use of palladium nanoparticles supported on graphene oxide in the Mizoroki-Heck reaction

We have developed a convenient single-step method for producing palladium nanoparticles on the surface of graphene oxide by reducing palladium chloride with NaBH₄. According to transmission electron microscopy data, palladium nanoparticles have a spheroidal shape; their sizes are 6–8 nm. The tests of immobilized palladium nanoparticles have shown that they exhibit high activity in the Mizoroki-Heck cross-coupling reaction.     

Preparation of an active Suzuki-Miyaura catalyst from nanoparticles obtained by deposition of palladium onto a polyvinyl alcohol support

Highly dispersed palladium was obtained by vacuum deposition onto polyvinyl alcohol films, followed by removal of the support via dissolution in hot water, and was characterized by transmission electron microscopy. The dispersed palladium consisted of aggregated nanoparticles with a size of ～10 nm and was used to catalyze the Suzuki-Miyaura reaction of p-iodonitrobenzene with phenylboronic acid in N,N-dimethylacetamide and propan-1-ol at 50–80°C in the presence of potassium phosphate as base. Taking into account that the reaction required atmospheric oxygen (no reaction occurred under argon), it was presumed that the process is homogeneous and that palladium is transferred into solution as a result of leaching by the action of oxygen in the presence of iodide ions. The properties of the examined catalytic system were compared with those reported for other catalytic systems containing palladium nanoparticles.     

Oxygen dissociation on palladium and gold core/shell nanoparticles

Oxygen dissociation reaction on gold, palladium, and gold‐palladium core/shell nanoparticles was investigated with plane wave basis set, density functional theory. Bader population analysis of charge and electron distribution was employed to understand the change of catalytic activity as a function of the nanopaticle composition. The nanoparticles’ electronic properties were investigated and the degree of core/shell charge polarization was estimated for each composition. It was found that surface polarization plays an important role in the catalysis of the initial step of electrophile reactions such as oxygen dissociation. We have investigated the O₂ adsorption energy on each nanoparticle and the activation barrier for the oxygen dissociation reaction as a function of the nanoparticle structure. Furthermore, we have investigated the influence of surface geometry, that is., surface bond lengths on the catalytic activity. We have compared the electronic and the geometry effects on the oxygen activation and dissociation. Our design rules for core/shell nanoparticles offer an effective method for control of the surface catalytic activity. Palladium and gold are often used as catalysts in synthetic chemistry. First‐principles calculations elucidate the mechanisms that control the surface reactivity of gold, palladium, and gold‐palladium core shell nanoparticles in oxygen dissociation reactions. Oxygen dissociation is promoted on the gold surface of gold/palladium core‐shell nanoparticles by favorable electron transfer from the core to the shell. Such core‐shell electronic effects can be used for fine‐tuning the nanoparticles catalytic activity.     

Metal Nanoparticles on Stainless Steel Surfaces as Novel Heterogeneous Catalysts

The goal of this work was the development of a novel type of heterogeneous catalyst, consisting of bare metal nanoparticles on stainless steel foils, which can be shaped to any kind of architecture and, if necessary, heated electrically. Solutions of pre-prepared, ligand protected and monodispersed gold, palladium, platinum and rhodium nanoparticles were sprayed onto stainless steel foils, followed by the careful removal of the ligand molecules by an oxygen plasma treatment. Due to this, bare particles become irreversibly fixed on the steel support. It could be shown that the original particle sizes do not change during the plasma treatment. Foils, densely coated with the nanoparticles, were used for gas phase catalyses in a self-made reactor at room temperature or at 60 °C. Hydrogenation of 1,3-butadiene at 15 nm Pd and 2 nm Pt, CO oxidation at 16 nm, 8 nm and 1.4 nm gold and NO reduction with NH₃ at 2 nm Rh particles were performed, indicating that the novel catalysts might in principle be applicable in technical processes if the experimental conditions like form and temperature would be optimized. Dedicated to Professor Dieter Fenske on the occassion of his 65th birthday.     

The effect of surface properties on visible luminescence of nanosized colloidal ZnO membranes

Luminescence properties of nanosized zinc oxide (ZnO) colloids depend greatly on their surface properties, which are in turn largely determined by the method of preparation. ZnO nanoparticles in the size range from 3 to 9 nm were prepared by addition of tetramethylammonium hydroxide ((CH3)4NOH) to an ethanolic zinc acetate solution. X-ray diffraction (XRD) indicates nanocrystalline ZnO membranes with polycrystalline hexagonal wurtzite structure. The ZnO membranes have a strong visible-emission intensity and the intensity depends upon hydrolysis time. The infrared spectra imply a variety of forms of zinc acetate complexes present on the surface of ZnO particles. The effect of the ZnO membrane surface properties on photoluminescence is discussed.     

Size control and catalytic activity of bio-supported palladium nanoparticles

The development of nanoparticles has greatly improved the catalytic properties of metals due to the higher surface to volume ratio of smaller particles. The production of nanoparticles is most commonly based on abiotic processes, but in the search for alternative protocols, bacterial cells have been identified as excellent scaffolds of nanoparticle nucleation, and bacteria have been successfully employed to recover and regenerate platinum group metals from industrial waste. We report on the formation of bio-supported palladium (Pd) nanoparticles on the surface of two bacterial species with distinctly different surfaces: the gram positive Staphylococcus sciuri and the gram negative Cupriavidus necator. We investigated how the type of bacterium and the amount of biomass affected the size and catalytic properties of the nanoparticles formed. By increasing the biomass:Pd ratio, we could produce bio-supported Pd nanoparticles smaller than 10nm in diameter, whereas lower biomass:Pd ratios resulted in particles ranging from few to hundreds of nm. The bio-supported Pd nanoparticle catalytic properties were investigated towards the Suzuki-Miyaura cross coupling reaction and hydrogenation reactions. Surprisingly, the smallest nanoparticles obtained at the highest biomass:Pd ratio showed no reactivity towards the test reactions. The lack of reactivity appears to be caused by thiol groups, which poison the catalyst by binding strongly to Pd. Different treatments intended to liberate particles from the biomass, such as burning or rinsing in acetone, did not re-establish their catalytic activity. Sulphur-free biomaterials should therefore be explored as more suitable scaffolds for Pd(0) nanoparticle formation.     

微米级MEL分子筛聚集体的制备(英文)

使用四丁基氢氧化铵-正硅酸四乙酯-水(TBAOH-TEOS-H2O)简单体系一步水热制备了具有多级孔道的微米级MEL结构分子筛聚集体.得到的silicalite-2微米球直径大于10μm且具有高达460 m2·g-1的比表面积和0.74 cm3·g-1的孔体积.微米球的生成一定程度上解决了催化应用过程中催化剂的分离和回收问题.同时,水热晶化过程中由纳米粒子自组装而成的晶间介孔缩短了反应物分子的扩散路径,保持了分子筛纳米晶粒的优势.此外,钛活性位的引入并未明显影响MEL微米球的形貌和结构,含钛的MEL微米球TS(钛硅分子筛)-2在苯酚羟基化反应中具有与纳米尺寸TS-1(100-200 nm)相当的催化活性,且TS-2可以通过简单过滤得到,简化了纳米级TS-1的分离和回收过程.     

Dense ceramic catalytic membranes and membrane reactors for energy and environmental applications

Catalytic membrane reactors which carry out separation and reaction in a single unit are expected to be a promising approach to achieve green and sustainable chemistry with less energy consumption and lower pollution. This article presents a review of the recent progress of dense ceramic catalytic membranes and membrane reactors, and their potential applications in energy and environmental areas. A basic knowledge of catalytic membranes and membrane reactors is first introduced briefly, followed by a short discussion on the membrane materials including their structures, composition and strategies for material development. The configuration of catalytic membranes, the design of membrane reaction processes and the high temperature sealing are also discussed. The performance of catalytic membrane reactors for energy and environmental applications are summarized and typical catalytic membrane reaction processes are presented and discussed. Finally, current challenges and difficulties related to the industrialization of dense ceramic membrane reactors are addressed and possible future research is also outlined.     

Synthesis and characterization of palladium containing membranes based upon polyacrylic acid

Different methods are described to synthesize a highly porous polymer membrane with fine dispersed metal-nanoparticles. The preparation of the porous catalytic membranes happens by crosslinking of polyacrylic acid dispersions with bifunctional crosslinker in presence of palladium particles. Palladium-nanoparticles, stabilized with the block copolymer polystyrene-block-polyethyleneoxide, can be immobilized in the polymer network in different ways. The polymer/metal network can be prepared in the form of thin flat membranes and dried under retention of the porosity and three-dimensional network structure. Different reduction and preparation methods were applied in order to obtain differences in particle size and distribution of the palladium. The morphology of the material was investigated by scanning electron microscopy. Transmission electron microscopy was employed to show the size and distribution of the metal-nanoparticles in the polymeric matrix. The catalytic activity of the obtained membranes was investigated for the gas phase hydrogenation of cyclohexene and propyne.