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Showing papers on "Catalyst support published in 2003"


Journal ArticleDOI
TL;DR: In this article, the use of carbon nanotubes (CNT) and nanofibers as catalysts and catalysts supports has been analyzed from the early 1990s until the beginning of 2003.
Abstract: This review analyses the literature from the early 1990s until the beginning of 2003 and covers the use of carbon nanotubes (CNT) and nanofibers as catalysts and catalysts supports. The article is composed of three sections, the first one explains why these materials can be suitable for these applications, the second describes the different preparation methods for supporting metallic catalysts on these supports, and the last one details the catalytic results obtained with nanotubes or nanofibers based catalysts. When possible, the results were compared to those obtained on classical carbonaceous supports and explanations are proposed to clarify the different behaviors observed.

1,742 citations


Journal ArticleDOI
27 Jun 2003-Science
TL;DR: Hydrogen was produced by aqueous-phase reforming of biomass-derived oxygenated hydrocarbons at temperatures near 500 kelvin over a tin-promoted Raney-nickel catalyst, which compares favorably with that of platinum-based catalysts for production of hydrogen from ethylene glycol, glycerol, and sorbitol.
Abstract: Hydrogen (H2) was produced by aqueous-phase reforming of biomass-derived oxygenated hydrocarbons at temperatures near 500 kelvin over a tin-promoted Raney-nickel catalyst. The performance of this non-precious metal catalyst compares favorably with that of platinum-based catalysts for production of hydrogen from ethylene glycol, glycerol, and sorbitol. The addition of tin to nickel decreases the rate of methane formation from C-O bond cleavage while maintaining the high rates of C-C bond cleavage required for hydrogen formation.

880 citations


Journal ArticleDOI
TL;DR: In particular, the extent of methanol and/or H2 combustion at differential O2 conversion is strongly dependent on the ease of copper oxidation in the catalyst and the redox properties of the catalyst appear to play a key role in determining the pathway for H2 production as discussed by the authors.

367 citations


Journal ArticleDOI
TL;DR: In this article, the authors summarized the progress which have been made in this area, often related to new methods of preparation of supports, active phases deposition or activation procedures, and examined the properties of active phases supported on oxides, pure or mixed, basic and acidic supports, zeolites, mesoporous materials, carbon and clays.

361 citations


Journal ArticleDOI
TL;DR: In this article, a nickel boride catalyst (NixB) was used for catalytic hydrolysis of alkaline NaBH4 solution and it was found that after heat treatment at 150°C in vacuum the NixB catalyst shows greatly enhanced catalytic activity and operational stability.

320 citations


Journal ArticleDOI
TL;DR: In this paper, the synthesis of supported metal and metal oxide catalysts using impregnation of an aqueous solution of chelated metal ions followed by drying is reviewed, and several examples are dealt with in some detail, in particular supported iron, nickel and cobalt-molybdenum catalysts.

309 citations


Journal ArticleDOI
TL;DR: In this article, the preparation methods of supported platinum catalysts, their microstructural characteristic and their effect on both thermal and in cell conditions stability are reviewed, as well as the effect of these catalysts on fuel cell performance.
Abstract: Supported platinum electrocatalysts are generally used in low temperature fuel cells to enhance the rates of the hydrogen oxidation and oxygen reduction reactions. In such catalysts, the high surface to volume ratios of the platinum particles maximize the area of the surfaces available for reaction. It is the structure and proper dispersal of these platinum particles that make low-loading catalysts feasible for fuel cell operation, lowering the cost of the system. If the platinum particles cannot maintain their structure over the lifetime of the fuel cell, change in the morphology of the catalyst layer from the initial state will result in a loss of electrochemical activity. This loss of activity in the platinum/carbon catalysts due to the agglomeration of platinum particles is considered to be a major cause of the decrease in cell performance, especially in the case of the cathode. In the light of the latest advances on this field, this paper reviews the preparation methods of these catalysts, their microstructural characteristic and their effect on both thermal and in cell conditions stability.

297 citations


Journal ArticleDOI
TL;DR: In this paper, aqueous-phase reforming of 10 wt% ethylene glycol solutions was studied at temperatures of 483 and 498 K over Pt-black and Pt supported on TiO2, Al2O3, carbon, SiO2 and ZrO2.
Abstract: Aqueous-phase reforming of 10 wt% ethylene glycol solutions was studied at temperatures of 483 and 498 K over Pt-black and Pt supported on TiO2, Al2O3, carbon, SiO2, SiO2-Al2O3, ZrO2, CeO2, and ZnO. High activity for the production of H2 by aqueous-phase reforming was observed over Pt-black and over Pt supported on TiO2, carbon, and Al2O3 (i.e., turnover frequencies near 8-15 min-1 at 498 K); moderate catalytic activity for the production of hydrogen is demonstrated by Pt supported on SiO2-Al2O3 and ZrO2 (turnover frequencies near 5 min-1); and lower catalytic activity is exhibited by Pt supported on CeO2, ZnO, and SiO2 (H2 turnover frequencies lower than about 2 min-1). Pt supported on Al2O3, and to a lesser extent ZrO2, exhibits high selectivity for production of H2 and CO2 from aqueous-phase reforming of ethylene glycol. In contrast, Pt supported on carbon, TiO2, SiO2-Al2O3 and Pt-black produce measurable amounts of gaseous alkanes and liquid-phase compounds that would lead to alkanes at higher conversions (e.g., ethanol, acetic acid, acetaldehyde). The total rate of formation of these byproducts is about 1-3 min-1 at 498 K. An important bifunctional route for the formation of liquid-phase alkane-precursor compounds over less selective catalysts involves dehydration reactions on the catalyst support (or in the aqueous reforming solution) followed by hydrogenation reactions on Pt.

280 citations


Journal ArticleDOI
TL;DR: The successful preparation of supported metal catalysts using dendrimer-encapsulated Pt nanoparticles as metal precursors and the effects of catalyst preparation and activation on activity for toluene hydrogenation and CO oxidation catalysis are discussed.
Abstract: 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.

258 citations


Journal ArticleDOI
TL;DR: In this article, multiwalled carbon nanotubes (MWCNTs) were synthesized in a catalytic reaction using CaCO3 as catalyst support, which enabled the production of MWCNTs in a fixed-bed flow reactor at relatively low reaction temperature.

238 citations


Journal ArticleDOI
TL;DR: In this paper, the carbon-supported PtRu electrocatalyst (1:1 atomic ratio) in acid media was investigated on the methanol electrooxidation, and the reaction order with respect to methanol was found to be 0.5.

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the deactivation of an industrial catalyst and a supported ruthenium catalyst, and evaluated their deactivation mechanisms, and a scheme of the reaction network was set up.
Abstract: Hydrogenation of aqueous glucose solution was performed in batch and continuous reactors using supported nickel and ruthenium catalysts. Preparation methods were precipitation, impregnation, sol-gel and template syntheses, and SiO2, TiO2, Al2O3 and carbon were used as support materials. A procedure for the one-step synthesis of templated metal on support catalysts was established. The influence of support material and preparation methods was studied and the results were compared with those of an industrial nickel catalyst. In a detailed study taking more than 1100 h time on stream we investigated the deactivation of the industrial catalyst and a supported ruthenium catalyst, and evaluated the deactivation mechanisms. As yet unpublished side products of the glucose hydrogenation were identified and a scheme of the reaction network was set up.

Journal ArticleDOI
TL;DR: In this paper, gold-based catalysts have been used to remove carbon monoxide impurities from the hydrogen feedstock streams used for fuel cells and to reduce the capital cost of fuel cell installations.

Journal ArticleDOI
TL;DR: The direct formation of H 2 O 2 from H 2 and O 2 is an attractive alternative to the current technology that involves the hydrogenation of an alkylanthroquinone to the corresponding hydroquinone, followed by the reaction of the hydro-quinone with oxygen to yield H 2O 2, although there is evidence that the addition of small amounts of platinum may enhance the yield of peroxide as discussed by the authors.

Journal ArticleDOI
TL;DR: In this paper, the authors compare biphasic reactions with their monophasic equivalents, and find that rates are lower in two-phase systems, mainly due to the fact that when the catalyst is in one phase and the substrates are in another, the interaction between the catalyst and the substrate is lower than in a monphasic system, thus reducing the rate of the reactions.

Journal ArticleDOI
TL;DR: In this paper, the use of 9% La2NiO4/γ-Al2O3 (9NLA) as a catalyst for CO2 reforming of methane to syngas has been investigated in a fixed-bed reactor.
Abstract: The use of 9% La2NiO4/γ-Al2O3 (9NLA) as a catalyst for CO2 reforming of methane to syngas has been investigated in a fixed-bed reactor. The results revealed that the yields of CO and H2 over a 800 °C calcined 9NLA catalyst were remarkably higher than those over a 500 °C calcined one. The BET data confirmed that the properties, such as specific surface area, pore volume and average pore diameter, of a used and a regenerated catalyst were similar to those of a fresh catalyst. Temperature-programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS) results indicated that the activity of the catalyst depended largely on the degree of catalyst reduction, as well as on the dispersion of metallic nickel. The results of X-ray diffraction (XRD) and temperature-programmed oxidation (TPO)-MS studies demonstrated that the formation of carbon species on the catalyst could be related to the structure and surface composition of the catalyst. With the rise in temperature for catalyst calcination, there was a decline in coke formation due to the formation of a stable NiAl2O4 spinel structure.

Journal ArticleDOI
TL;DR: A simply prepared water-soluble polyoxometalate synthesized from readily available zinc and tungsten salts is demonstrated to be an effective catalyst for selective alcohol oxidation with hydrogen peroxide in biphasic (water-alcohol) reaction media.
Abstract: We have demonstrated that a simply prepared water-soluble polyoxometalate, Na12[WZnZn2(H2O)2(ZnW9O34)2], synthesized from readily available zinc and tungsten salts in the presence of nitric acid, is an effective catalyst for selective alcohol oxidation with hydrogen peroxide in biphasic (water−alcohol) reaction media. Experiments have shown that the “self-assembled” catalyst in its mother liquor was as active as the isolated catalyst. The aqueous catalyst solution is easily separated from the water-insoluble products and can be recycled without loss in activity or selectivity.

Journal ArticleDOI
TL;DR: In this paper, the authors discuss recent work and future directions with zeolite X containing exchanged alkali metal cations, occluded aluminosilicate molecular sieves that have great potential as basic catalysts and catalyst supports and illustrate important principles that can be used to guide future design of shape selective base catalysts.

Journal ArticleDOI
31 Jul 2003-Nature
TL;DR: A tungsten catalyst for the solvent-free hydrosilylation of ketones is described that retains its activity until essentially all of the liquid substrate is converted to liquid products, which can then be decant to separate the catalyst that precipitates from the products of the reaction.
Abstract: Homogeneous catalysts—which exist in the same (usually liquid) phase as reactants and products—are usually more selective than heterogeneous catalysts and far less affected by limitations due to slow transport of reactants and products, but their separation from reaction products can be costly and inefficient. This has stimulated the development of strategies that facilitate the recycling of homogeneous catalysts1,2,3,4. Some of these methods exploit the preference of a catalyst for one of two solvents with thermoregulated miscibility5,6; others exploit a dramatic decrease in catalyst solubility as one reagent is consumed7,8 or temperature changed after completion of the reaction9,10,11,12,13,14. Here we describe a tungsten catalyst for the solvent-free hydrosilylation of ketones that retains its activity until essentially all of the liquid substrate is converted to liquid products, which we can then simply decant to separate the catalyst that precipitates from the products of the reaction. We attribute the ability of the catalyst to retain its solubility and hence activity until completion of the reaction to the transient formation of liquid clathrate15,16 that contains a few molecules of the substrate per molecule of the otherwise solid catalyst. Insights into the fundamental processes controlling the formation of this liquid clathrate might help to tailor other catalysts and substrates, so as to develop efficient and solvent-free schemes for reactions of practical interest.

Journal ArticleDOI
TL;DR: In this paper, a comparison of Au/SiO2 with Au/Al2O3 and Au/TiO2, which were prepared by both gas-phase grafting and liquid-phase methods and were active for CO oxidation at 273 K, showed that there were no appreciable differences in their catalytic activities as far as Au is deposited as nanoparticles with strong interaction.
Abstract: In order to clarify the support effect on CO oxidation over Au catalysts without the influence of the size effect of Au, Au was deposited on a variety of supports with high dispersion by gas-phase grafting (GG) of an organo-gold complex. Comparison of Au/SiO2 with Au/Al2O3 and Au/TiO2, which were prepared by both GG and liquid-phase methods and were active for CO oxidation at 273 K, showed that there were no appreciable differences in their catalytic activities as far as Au is deposited as nanoparticles with strong interaction. However, Au deposited onto the acidic supports, such as silica–alumina and activated carbon (AC), exhibited a much lower CO oxidation catalytic activity than those of the active Au catalysts, such as Au/TiO2.

Journal ArticleDOI
TL;DR: The results of temperature-programmed reduction show that the weaker interaction between the Mo and Ni species and the silica-alumina support leads to better reducibility of the metal oxides on silica alumina than on Al 2 O 3 as discussed by the authors.

Journal ArticleDOI
TL;DR: In this paper, a family of iron and cobalt catalysts with different alpha values with the objective of providing the option of producing a broad slate of fuel and chemical products was developed.

Journal ArticleDOI
TL;DR: In this article, specific catalysts were synthesized for modifying interactions between the support and the cobalt precursor, promoting reduction, stabilizing catalysts to high-temperature treatments, minimizing deleterious support metal interactions, and controlling the distribution of cobalt on large support particles.
Abstract: Controlling preparation variables in supported cobalt Fischer–Tropsch catalysts has a dramatic effect on the dispersion and distribution of cobalt, and determines how active and selective the resulting catalyst will be. We detail specific examples of catalyst synthesis strategies for modifying interactions between the support and the cobalt precursor, promoting reduction, stabilizing catalysts to high-temperature treatments, minimizing deleterious support metal interactions, and controlling the distribution of cobalt on large support particles. It is important to optimize the support and precursor interaction strength, so that it is strong enough to obtain good dispersion but not too strong to prevent low temperature reduction. We show examples in which formation of surface complexes and epitaxial matching of precursor and support structures improves dispersion dramatically. Reduction promoters can help in those cases where support–precursor interactions are too strong. We show how substitutions of silicon into a titania lattice stabilizes surface area and retards formation at high oxidation temperatures of cobalt ternary oxides that reduce only at very high temperatures—an important consideration if oxidative coke removal is necessary. In addition, surface treatment of TiO2 with an irreducible oxide like ZrO2 can inhibit deleterious support interactions that can block surface cobalt sites. Selectivity can also be dramatically altered by catalyst synthesis. We illustrate a case of large (2 mm) SiO2 particles onto which cobalt can be added either uniformly or in discrete eggshells, with the eggshell catalysts having substantially higher C5+ selectivity. These approaches can lead to optimal Fischer–Tropsch catalysts with high activity and C5+ selectivity, good physical integrity, and a long life.

Journal ArticleDOI
Zhenlu Wang1, Qingsheng Liu1, Jianfeng Yu1, Tonghao Wu1, Guojia Wang1 
TL;DR: In this article, the surface structures of these catalysts were characterized by various techniques, including BET, XRD, FTIR, XPS, TPR, and ESR.
Abstract: Supported copper on silica catalysts prepared by sol–gel and impregnation methods were studied in this paper. The surface structures of these catalysts were characterized by various techniques, including BET, XRD, FTIR, XPS, TPR, and ESR. The results showed that the distribution of copper species was in different ways in the catalysts prepared by the two methods. Cu(II) species highly dispersed in the silica matrix for the sol–gel catalyst, while copper oxide clusters are dominant in the CuO-SiO 2 sample prepared by the impregnation method. The catalysts were then used for dehydrogenation of 2-butanol. Obvious differences of catalytic behavior were observed for the catalysts prepared by the two methods. High selectivity (>90%) toward dehydrogenation and high 2-butanol conversion was observed for the impregnated catalyst; however, for the CuO-SiO 2 sol–gel catalyst, very low dehydrogenation selectivity and 2-butanol conversion were obtained. The surface structures of catalysts were closely related to the preparation methods, and the catalytic behaviors were affected subsequently. The copper oxide clusters, which may be reduced to Cu 0 , are responsible for the dehydrogenation reaction. The highly dispersed Cu(II) ions were inactive for catalyze 2-butanol dehydrogenation.

Journal ArticleDOI
Yu Hao1, Zhang Qunfeng1, Wei Fei1, Qian Weizhong1, Luo Guohua1 
01 Jan 2003-Carbon
TL;DR: In this paper, a model is proposed to explain the process of agglomerate formation and based on its formation mechanism, an approach to control CNT quality in an NAFBR is proposed.

Journal ArticleDOI
TL;DR: In this paper, the authors analyzed the effect of different support pre-treatment on the catalytic properties of Co catalysts and showed that the acetic acid-treated support has a negative effect on catalytic performance of Co catalyst, whereas the ammonium and ammonium nitrate-treated samples show pronounced effects on the catalyst performance.
Abstract: Alumina has been pretreated in the presence of medium and then used to prepare the supported Co catalysts. These modified supports and the respective catalysts have been thoroughly characterized by means of methods such as BET, pore size distribution, X-ray diffraction (XRD), ammonia temperature-programmed desorption (NH 3 -TPD), pyridine infrared spectroscopy (Py-FTIR), KBr-IR spectroscopy (FTIR), temperature-programmed reduction (TPR), oxygen titration, hydrogen chemisorption, in situ diffuse reflectance infrared Fourier transformation spectroscopy (DRIFTS) and CO hydrogenation to understand how chemically-treated alumina influences the properties of Co catalysts. These characterizations clearly show the changes of morphology (surface area, pore volume, pore size distribution and crystallite phase) as well as chemical properties (e.g. acidity) of the supports. Although the cobalt oxide crystallite sizes of the oxidic catalyst precursor are almost unaffected by different support pre-treatment, the reducibility of these catalysts vary greatly. And the support pre-treatment remarkably influences the adsorption and catalytic properties of these Co catalysts. The acetic acid-treated support has a negative effect on the catalytic properties of Co catalyst, whereas the ammonia and ammonium nitrate-treated samples show pronounced effects on the catalytic behaviors of Co catalysts.

Journal ArticleDOI
TL;DR: In this paper, the magnetic properties of various supported cobalt catalysts were characterized by magnetic measurements under ethanol steam-reforming conditions, in situ diffuse reflectance infrared spectroscopy and UV-Vis-NIR diffuse reflectances spectroscopic analysis.
Abstract: Various supported cobalt catalysts (Co/MgO, Co/Al2O3, Co/SiO2, Co/TiO2, Co/V2O5, Co/ZnO, Co/La2O3, Co/CeO2 and Co/Sm2O3), were characterised by magnetic measurements under ethanol steam-reforming conditions, in situ diffuse reflectance infrared spectroscopy and UV-Vis-NIR diffuse reflectance spectroscopy. Their magnetic behaviour was analysed as a function of reaction temperature and hydrogen treatment and was related to the cobalt species in the catalysts and to their catalytic behaviour in the steam-reforming of ethanol. The catalysts were prepared from Co2(CO)8 and used without previous calcination or reduction. All samples showed a paramagnetic or diamagnetic behaviour before reaction. The catalysts that performed well in the steam-reforming of ethanol presented under reaction conditions, metallic (ferromagnetic) cobalt particles and oxidised cobalt species. An easy exchange between small metallic cobalt particles (produced under H2 or under ethanol steam-reforming conditions) and oxidised cobalt species (produced under ethanol steam-reforming conditions) was found in these catalysts.

Patent
31 Jul 2003
TL;DR: In this paper, a method for growing single-wall carbon nanotubes involves preparing a catalyst comprising catalytic metals, iron and molybdenum, and magnesium oxide support material and contacting the catalyst with a gaseous carbon-containing feedstock at a sufficient temperature and for a sufficient contact time.
Abstract: A method for growing single-wall carbon nanotubes involves preparing a catalyst comprising catalytic metals, iron and molybdenum, and magnesium oxide support material and contacting the catalyst with a gaseous carbon-containing feedstock at a sufficient temperature and for a sufficient contact time to make single-wall carbon nanotubes. The weight ratio of iron and molybdenum can range from about 2 to 1 to about 10 to 1 and the metals loading up to about 10 wt% of the MgO. The catalyst can be sulfided. Methane is a suitable carbon-containing feedstock. The process can be conducted in batch, continuous or semi-continuous modes, in reactors, such as a transport reactor, fluidized bed reactor, moving bed reactors and combinations thereof. The process also includes making single-wall carbon nanotubes with catalysts comprising at least one Group VIB or Group VIIIB metal on supports such as magnesia, zirconia, silicia, and alumina, where the catalyst is sulfided.

Journal ArticleDOI
TL;DR: In this paper, the physicochemical properties of the catalysts were characterized using BET-surface area (BET-SA), XRD, TPR, TPD of NH3 and CO2.
Abstract: Novel catalysts comprising gold or ruthenium supported on hydroxyapatite are prepared by a deposition–precipitation method and examined for their behaviour in the water gas shift reaction at various reaction temperatures and at atmospheric pressure. The physicochemical properties of the catalysts were characterized using BET-surface area (BET-SA), XRD, TPR, TPD of NH3 and CO2. High WGS activities were observed over Au/HAP compared with Ru/HAP catalyst. The Ru/HAP catalyst showed methanation activity at temperatures above 300 °C, caused by a tendency for the dissociative chemisorption of CO to occur, though this process can be suppressed to some extent by an increase in the partial pressure of water under reaction conditions.

Journal ArticleDOI
TL;DR: In this article, X-ray diffraction (XRD) and BET techniques were used to identify the different Co species formed and the presence of Co 2+ species tetrahedrally and octahedral coordinated appears strongly influenced by the nature of the support and cobalt content.
Abstract: CoO x catalysts (Co 1 and 3 wt.%) were prepared by incipient-wetness impregnation of the supports, Al 2 O 3 and Al 2 O 3 (80 wt.%)-BaO (20 wt.%), and calcined at 500 and 800 °C. The samples were characterized by X-ray diffraction (XRD) and BET techniques. H 2 -temperature programmed reduction (TPR) and UV-Vis diffuse reflectance spectroscopy (DRS) spectra were recorded with the aim to identify the different Co species formed. The presence of Co 2+ species tetrahedrally and octahedrally coordinated appears strongly influenced by the nature of the support and the cobalt content. Co 3 O 4 particles were detected after calcination at 500 °C, a successive treatment at 800 °C promotes the dispersion of Co 3 O 4 clusters in the network of alumina with formation of CoAl 2 O 4 spinels. The catalysts were tested in the selective catalytic reduction (SCR) of NO with C 3 H 6 in the presence of excess O 2 , using a reactant mixture containing NO 1000 ppm, C 3 H 6 1000 ppm, O 2 5%. The effectiveness of the cobalt catalysts in the SCR process depends strongly on the type of support, metal loading and calcination temperature. The presence of barium oxide in the alumina network is effective in the stabilization on the surface of dispersed Co 2+ ions which are active and selective for NO reduction in excess of O 2 . Clusters of cobalt oxide, present as Co 3 O 4 in the alumina samples calcined at 500 °C, are active mainly for C 3 H 6 combustion.