Molecular sieving in a nanoporous b-oriented pure-silica-zeolite MFI monocrystal film

The molecular sieving property of a continuous b-oriented pure-silica-zeolite (PSZ) MFI monocrystal film was demonstrated in a zeolite-modified electrode (ZME) configuration using redox molecules of different sizes. Ru(NH3)63+ (diameter approximately 5.5 A) was able to traverse the film, while Co(phen)32+ (diameter approximately 13.0 A) was completely excluded. This film has excellent adhesion to the electrode and is stable in strong acidic conditions.     

Dendrimer-encapsulated nanoparticle precursors to supported platinum catalysts

In this contribution, we report the successful preparation of supported metal catalysts using dendrimer-encapsulated Pt nanoparticles as metal precursors. Polyamidoamine (PAMAM) dendrimers were first used to template and stabilize Pt nanoparticles prepared in solution. These dendrimer-encapsulated nanoparticles were then deposited onto a commercial high surface area silica support and thermally activated to remove the organic dendrimer. The resulting materials are active oxidation and hydrogenation catalysts. The effects of catalyst preparation and activation on activity for toluene hydrogenation and CO oxidation catalysis are discussed.     

Electrocrystallized platinum nanoparticle on carbon substrate

Platinum nanoparticles were electrocrystallized on a 4-aminophenyl monolayer-grafted carbon substrate. These Pt-modified surfaces were characterized by scanning tunneling microscopy (STM). The characterization by STM revealed that the platinum nanoparticles obtained had good size monodispersity and were well separated from one another on HOPG surfaces.     

Polyaniline-functionalized carbon nanotube supported platinum catalysts

Electrocatalytically active platinum (Pt) nanoparticles on a carbon nanotube (CNT) with enhanced nucleation and stability have been demonstrated through introduction of electron-conducting polyaniline (PANI) to bridge the Pt nanoparticles and CNT walls with the presence of platinum-nitride (Pt-N) bonding and π-π bonding. The Pt colloids were prepared through ethanol reduction under the protection of aniline, the CNT was dispersed well with the existence of aniline in the solution, and aniline was polymerized in the presence of a protonic acid (HCl) and an oxidant (NH(4)S(2)O(8)). The synthesized PANI is found to wrap around the CNT as a result of π-π bonding, and highly dispersed Pt nanoparticles are loaded onto the CNT with narrowly distributed particle sizes ranging from 2.0 to 4.0 nm due to the polymer stabilization and existence of Pt-N bonding. The Pt-PANI/CNT catalysts are electroactive and exhibit excellent electrochemical stability and therefore promise potential applications in proton exchange membrane fuel cells.     

Nanofaceted platinum surfaces: a new model system for nanoparticle catalysts

We present a novel model system for nanoparticle electrocatalysts. A surface consisting of alternating (100) and (111) facets, several nanometers across and nearly 1 microm long, were self-assembled by annealing Pt single crystal surfaces initially cut at the midpoint between [111] and [100] directions, i.e., Pt(1+ square root of 3 1 1). The formation of these self-assembled arrays of nanofacets was monitored by in-situ surface X-ray scattering. These surfaces were further characterized with scanning probe microscopy and cyclic voltammetry. We found that the Pt(1+ square root of 3 1 1) surface is flat with less than 1 nm rms roughness when it was annealed in argon/hydrogen atmosphere. Then the surface forms nanofacets when it is annealed in pure air. This nanofaceting transition was completely reversible and reproducible. We investigated effects of CO adsorption on the voltammetric characteristics of both hydrogen-annealed and air-annealed surfaces. We found that CO-adsorption/desorption cycles in CO containing electrolyte solution result in considerable modification of blank cyclic voltammograms for the both surfaces. We attributed these differences to the electrochemical annealing of surface defects due to the increased mobility during the cycles.     

Shape‐directed platinum nanoparticle synthesis: nanoscale design of novel catalysts

Platinum‐based catalytic materials have received significant attention, particularly in the shape and size control of faceted materials for catalysis. More recently, there has been a rapid increase in the number of reports of successful preparations in this field; however, a fundamental understanding of controlled growth towards catalytic material design is essential for future implementation and broad application. In this review, we provide an overview of the recent findings reported since 2009, focusing on methods for shape control as well as the effects of exposed surface facets on select catalytic reactions. Copyright © 2013 John Wiley & Sons, Ltd.     

纳米碳材料负载铂催化剂在环己烷脱氢反应中的催化性能研究

制备了纳米碳材料负载铂的催化剂,通过N₂吸附、TEM、XRD技术分别对载体的BET比表面积和催化剂结构、形貌和粒径大小进行了表征。考察了不同催化剂在环己烷脱氢反应中的催化性能以及温度对纳米碳颗粒负载铂催化剂活性的影响。结果表明,锚定在不同碳载体上的铂有较好的分散性,粒径较小,粒度分布范围较窄并且具有相同的晶型结构。孔状纳米碳颗粒负载铂催化剂的活性高于碳纳米管和高比表面的活性炭负载铂催化剂,并且在低温条件下已经显示了较高的活性,尤其是中空碳颗粒负载铂催化剂在环己烷脱氢反应中显示了好的活性和稳定性。     

Electrochemically-assisted deposition of oxidases on platinum nanoparticle/multi-walled carbon nanotube-modified electrodes

Platinum nanoparticles were electrodeposited by a multi-potential step technique onto a multi-walled carbon nanotube (MWCNT) film pre-casted on a glassy carbon (GC) or boron-doped diamond (BDD) electrode. The MWCNT network consisted of Pt nanoparticles with an average diameter of 120 nm after an optimization of 36 deposition cycles. The resulting electrochemical sensors were capable of detecting hydrogen peroxide as low as 25 nM. Five different enzymes: glucose, lactate, glutamate, amino acid and xanthine oxidases, respectively, were deposited by a constant current technique for 5-10 min to form a stable and active biolayer for the analysis of their corresponding analytes. The glucose oxidase-based biosensor was linear up to 10 mM glucose with a detection limit of 250 nM and a response time of 5 s. Similar response times and detection limits were observed with glutamate, lactate, and amino acid oxidase despite the fact that the linear ranges were noticeably narrower. The mechanism of deposition was attributed to the decrease of local pH, created by oxygen evolution and effected enzyme precipitation.     

应用于氧还原反应的石墨烯-无定形碳核壳结构复合材料载铂催化剂(英文)

采用氯化法制备石墨烯-无定型碳复合材料(GNS@a-C),并用作质子交换膜燃料电池(PEMFC)氧还原反应Pt催化剂的载体.结果显示,所制Pt/GNS@a-C催化剂与传统商业催化剂Pt/C相比,有较好的活性和较高的稳定性:质量活性(0.121 A/mg)几乎是Pt/C(0.064 A/mg)的两倍.更重要的是,该新型催化剂加速4000圈后其电化学活性面积保留了最初的51%,与Pt/C的33%相比,前者有更好的电化学稳定性,显示它在PEMFC中将具有较好的应用潜力.     

Property and structure of various platinum catalysts for low-temperature carbon monoxide oxidations

The oxidation of carbon monoxide (CO) has received more attention in the last two to three decades owing to its importance in different fields. To control this CO pollution, catalytic converters have been investigated. Different types of catalysts have been used in a catalytic converter for CO emission control purposes. Platinum (Pt)-based noble metal catalysts show great potential for CO oxidation in catalytic converters with high thermal stability and tailoring flexibility. Pt metal catalysts modified with promoters such as alkali metals and reducible metal oxides have received great attention for their superior catalytic activities in CO oxidation. Temperature, close environment of the catalyst, and chemical composition in the surface layer of the catalyst have a huge effect on the active phase dispersion and O₂ adsorption capacity of the Pt metal catalysts. The main difference in activities of Pt metal catalyst for CO oxidation in O₂ or H₂ atmosphere has found. The addition of supports in Pt metal catalysts has improved their performances and reduced their cost. These improvement strongly depends on the surface structure, morphology, number of active sites, and various Pt-O interactions. Many research articles have already been published in CO oxidation over Pt metal catalysts, but no review article dedicated to CO oxidation is available in the literature.     

Preparation of hydrogenation catalysts based on platinum nanoparticles supported on carbon nanomaterials

Hydrogenation catalysts as platinum nanoparticles supported on carbon nanomaterials (singleand multi-walled nanotubes, nanofibers, and fullerene black) have been obtained by modifying the platinum precursor with an organic base. A support pretreatment procedure for producing carboxyl groups on the nanotube and nanofiber surface is suggested.     

Nanoparticle size effects on methanol electrochemical oxidation on carbon supported platinum catalysts

The particle size effect observed on the performance of Pt/C electrocatalysts toward the methanol oxidation reaction (MOR) has been investigated with differential electrochemical mass spectrometry (DEMS). The investigation has been conducted under both potentiodynamic and potentiostatic conditions as research on methanol electrochemical oxidation is closely related to interest in direct methanol fuel cells. The particle size effect observed on the MOR is commonly regarded as a reflection of different Pt-CO and Pt-OH bond strengths for different particle sizes. This work focuses mainly on the mechanism of methanol dehydrogenation on platinum which is central to the problem of the optimization of the efficiency of methanol electro-oxidation by favoring the CO(2) formation pathway. It was found that the partitioning of the methanol precursor among the end products on supported platinum nanoparticles is strongly dependent on particle size distribution. Also, it is postulated that the coupling among particles of different sizes via soluble products must be considered in order to understand the particle size effects on the observed trends of product formation. An optimum particle size range for efficiently electro-oxidizing methanol to CO(2) was found between 3 and 10 nm, and loss in efficiency is mostly related to the partial oxidation of methanol to formaldehyde on either too small or too large particles. The possible reasons for these observations are also discussed.     

Electrocatalytic properties of the catalysts based on carbon nanofibers with various platinum contents

The catalysts on carbon nanofibers with various platinum contents were synthesized. The morphology, resistance to oxidation, and electrochemical behavior of the catalysts in the reactions that occur in fuel cells were studied. The dependence of the specific output of cathodes of hydrogen—air fuel cells on the sizes of the platinum clusters was established.     

Size control of metal nanoparticle catalysts for the gas-phase synthesis of single-walled carbon nanotubes

Nanoparticle catalysts are essential and indispensable for all syntheses of single-walled carbon nanotubes (SWCNTs). We have prepared size-controlled Co, Co-Mo, and Fe-Mo nanoparticles by the reversed micelle method as the catalysts for the gas-phase pyrolytic synthesis of SWCNTs. From the investigation of the relation between the sizes of the nanoparticles and the alkyl-chain lengths of the cationic surfactants, dialkyldimethylammonium bromides, it has been found that the alkyl groups of the surfactants could play a role in controlling the sizes of the nanoparticles and that the alkyl chain of the surfactant should be preferably less than 10 carbon atoms at most to prepare smaller-size nanoparticles with a narrow size distribution. The reduction of the particle size increases the number of nanoparticles in the colloidal solution and leads to a higher yield of SWCNTs.     

Spectrophotometric determination of platinum in experimental catalysts

Conditions have been established and procedures are described for the colorimetric determination of platinum in experimental catalysts and miscellaneous materials. The methods are based on the measurement of the intensity of colour produced by the reaction of chloroplatinic acid with tin(II) chloride. Interference from metals such as chromium, molybdenum and nickel, which are often also present in catalysts, is overcome by selective extraction of the complex into isoamyl alcohol followed by measurement of the absorbance of the alcohol layer.     

Synergistic assembly of dendrimer-templated platinum catalysts on nitrogen-doped carbon nanotube electrodes for oxygen reduction

A study of the synergistic tuning of nitrogen-doped carbon nanotubes (NCNTs) as support- and size-monodisperse platinum nanoparticles templated from G4-NH2 dendrimers (Pt-DEN's) as catalysts targeted toward oxygen reduction is reported. UV-vis spectroscopy, adsorption isotherms, TGA, TEM, and voltammetry were used to characterize the loading and activity of Pt-DENs immobilized on CNT and NCNT supports. The facile uptake of Pt-DENs was found to be influenced by the number of edge plane sites on the NCNT support with higher adsorption rates observed for NCNTs with increased nitrogen content. Pt-DEN/NCNT composites exhibit high activity with a mass-transport-limited current density and mass activity of 2.3 mA cm(-2) and 0.05 mA g(-1), respectively, for the oxygen reduction reaction (ORR).     

Molecular dynamics simulations of the interactions between platinum clusters and carbon platelets

Molecular dynamics simulations have been performed with two reactive force fields to investigate the structure of a Pt100 cluster adsorbed on the three distinct sides of a carbon platelet. A revised Reax force field for the carbon-platinum system is presented. In the simulations, carbon platelet edges both with and without hydrogen termination have been studied. It is found that the initial mismatch between the atomic structure of the platelet egde and the adsorbed face of the Pt100 cluster leads to a desorption of a few platinum atoms from the cluster and the subsequent restructuring of the cluster. Consequently, the average Pt-Pt bond length is enlarged in agreement with experimental results. This change in the bond length is supposed to play an important role in the enhancement of the catalytic activity, which is demonstrated by studying the changes in the bond order of the platinum atoms. We found an overall shift to lower values as well as a loss of the well-defined peak structure in the bond-order distribution.     

Geometric effects in methylcyclopentane hydrogenolysis on platinum catalysts

Methylcyclopentane hydrogenolysis was studied at 493 K over variously dispersed platinum catalysts. The relative contributions of the predominant hydrogenolysis mechanisms are correlated to the particle size in agreement with a simple geometric model.

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