Showing papers on "Catalysis published in 2002"
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01 Jan 2002
TL;DR: The early years of Ionic liquid production were covered in this article, where a new generation of soluble supports for Supported Organic Synthesis (SPOS) was proposed. But this support was not applied to the task-specific Ionic liquids.
Abstract: Preface A Note From The Editors THE EARLY YEARS OF IONIC LIQUIDS SYNTHESIS AND PURIFICATION Synthesis Quality Aspects and other Questions Related to Commercial Ionic Liquid Production Synthesis of Task-specific Ionic Liquids PHYSICO-CHEMICAL PROPERTIES Melting Points Viscosity and Density Solubility and Solvation in Ionic Liquids Gas Solubilities Polarity Electrochemistry STRUCTURE AND DYNAMICS Order in the Liquid State and Structure Computational Modelling of Ionic Liquids Translational Diffusion Molecular Reorientational Dynamics ORGANIC SYNTHESIS Ionic Liquids in Organic Synthesis: Effects on Rate and Selectivity Stoicheiometric Organic Reactions and Acid-catalysed Reactions in Ionic Liquids Transition Metal Catalysis in Ionic Liquids Ionic Liquids in Multiphasic Reactions Task Specific Ionic Liquids (TSILs): A New Generation of Soluble Supports for Supported Organic Synthesis (SPOS) Supported Ionic Liquid Phase Catalysts Multiphasic Catalysis Using Ionic Liquids in Combination with Compressed CO2 INORGANIC SYNTHESIS Directed Inorganic and Organometallic Synthesis Making of Inorganic Materials by Electrochemical Methods Ionic Liquids in Material Synthesis: Functional Nanoparticles and Other Inorganic Nanostructures POLYMER SYNTHESIS IN IONIC LIQUIDS BIOCATALYTIC REACTIONS IN IONIC LIQUIDS INDUSTRIAL APPLICATIONS OF IONIC LIQUIDS CONLUDING REMARKS AND OUTLOOK
3,423 citations
1,708 citations
TL;DR: In this paper, states of chemisorbed H that can be involved in the mechanism of the cathodic H2 evolution reaction (HER) at metals, specially Pt, and the reverse oxidation reaction (HOR), are examined.
1,507 citations
TL;DR: In this paper, it was shown that for a class of catalytic reactions there is a universal, reactant independent relation between the reaction activation energy and the stability of reaction intermediates.
1,128 citations
TL;DR: The new ionic liquids combine the low volatility and ease of separation from product normally associated with solid acid catalysts, with the higher activity and yields normally found using conventional liquid acids.
Abstract: The reaction of triphenylphosphine or N-butylimidazole with cyclic sultones gives zwitterions that are subsequently converted into ionic liquids by reaction with trifluoromethane sulfonic acid or p-toluenesulfonic acid. The resulting ionic liquids have cations to which are tethered alkane sulfonic acid groups. These Bronsted acidic ionic liquids are useful solvent/catalysts for several organic reactions, including Fischer esterification, alcohol dehydrodimerization and the pinacol rearrangement. The new ionic liquids combine the low volatility and ease of separation from product normally associated with solid acid catalysts, with the higher activity and yields normally found using conventional liquid acids.
1,120 citations
TL;DR: In situ transmission electron microscopy is used to obtain atom-resolved images of copper nanocrystals on different supports, which are catalysts for methanol synthesis and hydrocarbon conversion processes for fuel cells.
Abstract: In situ transmission electron microscopy is used to obtain atom-resolved images of copper nanocrystals on different supports. These are catalysts for methanol synthesis and hydrocarbon conversion processes for fuel cells. The nanocrystals undergo dynamic reversible shape changes in response to changes in the gaseous environment. For zinc oxide-supported samples, the changes are caused both by adsorbate-induced changes in surface energies and by changes in the interfacial energy. For copper nanocrystals supported on silica, the support has negligible influence on the structure. Nanoparticle dynamics must be included in the description of catalytic and other properties of nanomaterials. In situ microscopy offers possibilities for obtaining the relevant atomic-scale insight.
1,080 citations
TL;DR: In this article, rare earth (RE=La3+, Ce3+, Er3+, Pr3+, Gd3+-doped, Nd3+, Sm3+, Nd4+, Sm5+ and Sm6+ were used as precursors for the synthesis of RE/TiO2 photocatalysts, which were characterized by XRD, IR, UV-vis diffuse reflection and transient absorption spectra.
1,067 citations
1,062 citations
TL;DR: The catalytic performance of Au nanoparticles is defined by three major factors: contact structure, support selection, and particle size, the first being the most important because the perimeter interfaces around Au particles act as the site for reaction as discussed by the authors.
Abstract: Gold in bulk is chemically inert and has often been regarded to be poorly active as a catalyst. However, when gold is small enough—with particle diameters below 10 nm—it turns out to be surprisingly active for many reactions, such as CO oxidation and propylene epoxidation. This is especially so at low temperatures. Here, a summary of the catalysis of Au nanoparticles deposited on base metal oxides is presented. The catalytic performance of Au is defined by three major factors: contact structure, support selection, and particle size, the first of which being the most important because the perimeter interfaces around Au particles act as the site for reaction.
1,042 citations
TL;DR: Layered double hydroxides (LDHs) have been investigated for many years as host materials for a range of anion exchange intercalation reactions as mentioned in this paper and have been used extensively as ion-exchange materials, catalysts, sorbents and halogen absorbers.
Abstract: Layered double hydroxides (LDHs) have been investigated for many years as host materials for a range of anion exchange intercalation reactions. In this role they have been used extensively as ion-exchange materials, catalysts, sorbents and halogen absorbers. More recently, there have been a tremendous number of new developments using these materials to store and deliver biologically active materials in vivo. Significant advances have been made recently on the characterisation of these materials, including structural studies and on the mechanism of intercalation using in situ techniques.
1,030 citations
TL;DR: Three methods are described, in the context of the guiding principles of green chemistry, for the catalytic oxidation of alcohols, using a recyclable oligomeric TEMPO catalyst and sodium hypochlorite as the oxidant in a bromide-free and chlorinated hydrocarbon solvent-free system.
Abstract: Three methods are described, in the context of the guiding principles of green chemistry, for the catalytic oxidation of alcohols. The first employs a recyclable oligomeric TEMPO catalyst (PIPO) and sodium hypochlorite as the oxidant in a bromide-free and chlorinated hydrocarbon solvent-free system. The second involves a ruthenium/TEMPO catalyst and oxygen as the oxidant. The third consists of a recyclable water-soluble palladium-diamine complex in conjunction with air as the oxidant in an aqueous biphasic system. The mechanisms of the ruthenium/TEMPO- and palladium-catalyzed oxidations are discussed, and the mechanism of the former is compared with that of the analogous copper/TEMPO catalyst.
TL;DR: Based on density functional theory calculations, kinetic measurements, microkinetic and Monte Carlo simulations, thermogravimetric analysis (TGA) experiments, extended X-ray absorption spectroscopy (EXAFS) measurements, and experimental results from the literature, this paper presented a detailed and comprehensive mechanistic picture of the steam reforming process on a Ni catalyst.
TL;DR: In this article, a review examines recent developments in the complete oxidation of methane at low temperature over noble metal based catalysts in patents and open literature, focusing on low-temperature reaction conditions.
Abstract: This review examines recent developments in the complete oxidation of methane at low temperature over noble metal based catalysts in patents and open literature. The abatement of natural gas vehicle (NGV) methane emissions is taken as one example among possible applications. The review develops current ideas about the properties of palladium and platinum catalysts supported on silica and alumina supports in the complete oxidation of methane under oxidising conditions, focusing on low-temperature reaction conditions. The influence of residual chloride ions on the catalytic activity, the kinetic aspects of the oxidation of methane over these catalysts, the nature of the active sites, the influence of metal particle size and reaction products on the activity, the observed changes in catalytic activity with reaction time and the effect of sulphur containing compounds are examined. The latest studies concerned with improved palladium and platinum supported catalysts which would exhibit enhanced and stable catalytic activity at low temperature in the presence of water and sulphur containing compounds are reported. Possible routes for preparing catalysts able to meet future regulations concerning methane emissions from lean-burn NGV vehicles are discussed.
TL;DR: The development of new palladium catalysts for the arylation of amines and alcohols with aryl halides and sulfonates is reviewed in this article, where modifications and improvements in technical aspects of reaction development are described where appropriate.
Abstract: The development of new palladium catalysts for the arylation of amines and alcohols with aryl halides and sulfonates is reviewed. Initial systems as well as mechanistic issues are discussed briefly, while subsequent generations of catalysts are described in greater detail. For these later generations of catalysts, substrate scope and limitations are also discussed. The review is organized by substrate class. Modifications and improvements in technical aspects of reaction development are described where appropriate. In addition, applications of this technology toward natural product synthesis, new synthetic methodology, and medicinal chemistry are chronicled. This review is organized in a manner that is designed to be useful to the synthetic organic chemist.
TL;DR: X-ray diffraction and absorption is used to show that LaFe0.05O3, one of the perovskite-based catalysts investigated for catalytic converter applications since the early 1970s, retains its high metal dispersion owing to structural responses to the fluctuations in exhaust-gas composition that occur in state-of-the-art petrol engines.
Abstract: Catalytic converters are widely used to reduce the amounts of nitrogen oxides, carbon monoxide and unburned hydrocarbons in automotive emissions. The catalysts are finely divided precious-metal particles dispersed on a solid support. During vehicle use, the converter is exposed to heat, which causes the metal particles to agglomerate and grow, and their overall surface area to decrease. As a result, catalyst activity deteriorates. The problem has been exacerbated in recent years by the trend to install catalytic converters closer to the engine, which ensures immediate activation of the catalyst on engine start-up, but also places demanding requirements on the catalyst's heat resistance. Conventional catalyst systems thus incorporate a sufficient excess of precious metal to guarantee continuous catalytic activity for vehicle use over 50,000 miles (80,000 km). Here we use X-ray diffraction and absorption to show that LaFe0.57Co0.38Pd0.05O3, one of the perovskite-based catalysts investigated1,2,3,4 for catalytic converter applications since the early 1970s, retains its high metal dispersion owing to structural responses to the fluctuations in exhaust-gas composition that occur in state-of-the-art petrol engines5. We find that as the catalyst is cycled between oxidative and reductive atmospheres typically encountered in exhaust gas, palladium (Pd) reversibly moves into and out of the perovskite lattice. This movement appears to suppress the growth of metallic Pd particles, and hence explains the retention of high catalyst activity during long-term use and ageing.
TL;DR: DMC possesses properties of nontoxicity and biodegradability which makes it a true green reagent to use in syntheses that prevent pollution at the source and avoiding the formation of undesirable inorganic salts as byproducts.
Abstract: Dimethyl carbonate (DMC) is a versatile compound that represents an attractive eco-friendly alternative to both methyl halides (or dimethyl sulfate) and phosgene for methylation and carbonylation processes, respectively. In fact, the reactivity of DMC is tunable: at T = 90 °C, methoxycarbonylations take place, whereas at higher reaction temperatures, methylation reactions are observed with a variety of nucleophiles. In the particular case of substrates susceptible to multiple alkylations (e.g., CH2-active compounds and primary amines), DMC allows unprecedented selectivity toward mono-C- and mono-N-methylation reactions. Nowadays produced by a clean process, DMC possesses properties of nontoxicity and biodegradability which makes it a true green reagent to use in syntheses that prevent pollution at the source. Moreover, DMC-mediated methylations are catalytic reactions that use safe solids (alkaline carbonates or zeolites), thereby avoiding the formation of undesirable inorganic salts as byproducts. The r...
TL;DR: In this paper, the cleavage and addition of ortho C−H bonds in various aromatic compounds such as ketones, esters, imines, imidates, nitrile, and aldehydes to olefins and acetlylenes can be achieved with the aid of ruthenium catalysts.
Abstract: The cleavage and addition of ortho C−H bonds in various aromatic compounds such as ketones, esters, imines, imidates, nitrile, and aldehydes to olefins and acetlylenes can be achieved catalytically with the aid of ruthenium catalysts. The reaction is generally highly efficient and useful in synthetic methods. The coordination to the metal center by a heteroatom in directing groups such as carbonyl and imino groups is the key. The reductive elimination to form a C−C bond is the rate-determining step.
TL;DR: It is reported that Ir(I) precursors in conjunction with bipyridine ligands catalyze in high yields the borylation of arenes under mild conditions, and that the reactions involve uncommon, Ir(II) tris-boryl complexes.
Abstract: The borylation of arenes leads to the formation of synthetically versatile products from unactivated arene reagents. We report that Ir(I) precursors in conjunction with bipyridine ligands catalyze in high yields the borylation of arenes under mild conditions. These reactions encompase arenes bearing both electron-withdrawing and electron-donating substituents. The temperatures required for the transformation are much lower than those previously reported for direct arene borylation. The combination of [Ir(COE)2Cl]2 and (4,4-di-t-butyl)bipyridine even allows for reaction at room temperature. The same catalyst system at 100 °C provides remarkably high turnover numbers for a hydrocarbon functionalization process. Mechanistic studies show that the reactions involve uncommon, Ir(II) tris-boryl complexes. An example of this type of complex ligated by di-t-butylbipyridine was isolated and structurally characterized. It reacted rapidly at room temperature to produce aryl boronate esters in high yields.
TL;DR: In this article, a comparative study of the oxygen reduction reaction on two carbon-supported Pt-based alloy catalysts in aqueous acidic electrolyte at low temperature is presented.
Abstract: We describe a comparative study of the oxygen reduction reaction on two carbon-supported Pt-based alloy catalysts in aqueous acidic electrolyte at low temperature. Both alloys have the bulk compositions of 50 and 75 at. % Pt, with the alloying elements being Ni and Co. Comparison is made to a pure Pt catalyst on the same carbon support, Vulcan XC-72, having the same metal loading (20 wt %) and nominally the same particle size (4 ± 2 nm). High-resolution electron microscopy was used to determine the size and shape of the particles as well as the particle size distribution on all catalysts. Electrochemical measurements were performed using the thin-film rotating ring−disk electrode method in 0.1 M HClO4 at 20−60 °C. Hydrogen adsorption pseudocapacitance was used to determine the number of Pt surface atoms and to estimate the surface composition of the alloy catalysts. Kinetic analysis in comparison to pure Pt revealed a small activity enhancement (per Pt surface atom) of ca. 1.5 for the 25 at. % Ni and Co c...
TL;DR: In this article, the plasmon band of the silver metal nanoparticles formed in situ are the active catalyst for reducing aromatic nitro compounds to amines in aqueous medium.
ENEA1
TL;DR: In this article, a detailed procedure for comparing high surface Pt/C catalysts was pointed out, and the real platinum metal surface area was evaluated by cyclic voltammetry on a thin porous coated disk electrode.
TL;DR: In this paper, it is concluded that although there is indirect, mainly spectroscopic, evidence for various reaction intermediates on the catalyst surface, it is difficult to confirm that any of these are involved in a critical mechanistic step because of a lack of a direct quantitative correlation between infrared and kinetic measurements.
Abstract: Research on the selective reduction of NOx with hydrocarbons under lean-burn conditions using non-zeolitic oxides and platinum group metal (PGM) catalysts has been critically reviewed. Alumina and silver-promoted alumina catalysts have been described in detail with particular emphasis on an analysis of the various reaction mechanisms that have been put forward in the literature. The influence of the nature of the reducing agent, and the preparation and structure of the catalysts have also been discussed and rationalised for several other oxide systems. It is concluded for non-zeolitic oxides that species that are strongly adsorbed on the surface, such as nitrates/nitrites and acetates, could be key intermediates in the formation of various reduced and oxidised species of nitrogen, the further reaction of which leads eventually to the formation of molecular nitrogen. For the platinum group metal catalysts, the different mechanisms that have been proposed in the literature have been critically assessed. It is concluded that although there is indirect, mainly spectroscopic, evidence for various reaction intermediates on the catalyst surface, it is difficult to confirm that any of these are involved in a critical mechanistic step because of a lack of a direct quantitative correlation between infrared and kinetic measurements. A simple mechanism which involves the dissociation of NO on a reduced metal surface to give N(ads) and O(ads), with subsequent desorption of N2 and N2O and removal of O(ads) by the reductant can explain many of the results with the platinum group metal catalysts, although an additional contribution from organo-nitro-type species may contribute to the overall NOx reduction activity with these catalysts. It is concluded, after the investigation of hundreds of catalyst formulations, that many of the fundamental questions relating to lean deNOx reactions have been addressed and the main boundary conditions have been established. It seems clear that catalysts with sufficient activity, selectivity or stability to satisfy the demanding conditions that appertain in automotive applications are still far away. The rapidly growing interest in NOx storage systems reflects this situation, and it now seems to be the case that acceptable direct NOx reduction catalysts may be very difficult to find for lean-burn applications.
TL;DR: In this paper, the role of Ni as a catalytically enhancing agent in the methanol oxidation process was investigated using cyclic voltammetry, chronoamperometry, X-ray photoelectron spectroscopy, transmission electron microscopy, and Xray diffraction.
Abstract: Electrooxidation of methanol in sulfuric acid solution was studied using Pt, Pt/Ni(1:1 and 3:1), Pt/Ru/Ni(5:4:1 and 6:35:05), and Pt/Ru(1:1) alloy nanoparticle catalysts, in relation to methanol oxidation processes in the direct oxidation methanol fuel cell The Pt/Ni and Pt/Ru/Ni alloys showed excellent catalytic activities compared to those of pure Pt and Pt/Ru The role of Ni as a catalytically enhancing agent in the oxidation process was interrogated using cyclic voltammetry, chronoamperometry, X-ray photoelectron spectroscopy, transmission electron microscopy, and X-ray diffraction X-ray diffraction data showed alloy formation for all Pt/Ni, Pt/Ru/Ni, and Pt/Ru nanoparticles, whereas X-ray photoelectron spectroscopy confirmed that chemical states of Pt were exclusively metallic The presence of metallic Ni, NiO, Ni(OH)2, NiOOH, metallic Ru, RuO2, and RuO3 was also confirmed We found that the Pt4f binding energies for the Pt/Ni and Pt/Ru/Ni alloy nanoparticles were lower than those for clean Pt na
TL;DR: The performance of formic acid fuel oxidation on a solid PEM fuel cell at 60°C was reported in this paper, where the anodic polarization potential of Formic acid is approximately 0.1 V lower than that for methanol on a standard Pt/Ru catalyst.
TL;DR: In this paper, the asymmetric conjugate addition of various carbon and heteroatom nucleophiles to nitroalkenes as a tool for the construction of highly functionalized synthetic building blocks is presented.
TL;DR: The new concept of supported ionic liquid catalysis involves the surface of a support material that is modified with a monolayer of covalently attached ionicLiquid fragments that serves as the reaction phase in which a homogeneous hydroformylation catalyst was dissolved.
Abstract: The new concept of supported ionic liquid catalysis involves the surface of a support material that is modified with a monolayer of covalently attached ionic liquid fragments. Treatment of this surface with additional ionic liquid results in the formation of a multiple layer of free ionic liquid on the support. These layers serve as the reaction phase in which a homogeneous hydroformylation catalyst was dissolved. Supported ionic liquid catalysis combines the advantages of ionic liquid media with solid support materials which enables the application of fixed-bed technology and the usage of significantly reduced amounts of the ionic liquid. The concept of supported ionic liquid catalysis has successfully been used for hydroformylation reactions and can be further expanded into other areas of catalysis.
TL;DR: Ir(0) nanoparticles with a mean diameter of 2 nm have been prepared by reduction of Ir(I) dissolved in the ionic liquid with H2 so that this catalytic solution can be reused several times for the biphasic hydrogenation of olefins under mild reaction conditions.
Abstract: 1-n-Butyl-3-methylimidazolium hexafluorophosphate room-temperature ionic liquid is not only suitable as a medium for the preparation and stabilization of iridium nanoparticles but also ideal for the generation of recyclable biphasic catalytic systems for hydrogenation reactions. Thus, Ir(0) nanoparticles with a mean diameter of 2 nm have been prepared by reduction of Ir(I) dissolved in the ionic liquid with H2. This catalytic solution can be reused several times for the biphasic hydrogenation of olefins under mild reaction conditions.