Showing papers on "Catalyst support published in 2008"

PEM fuel cell electrocatalysts and catalyst layers : fundamentals and applications

Abstract: PEM Fuel Cell Fundamentals Electrocatalytic Oxygen Reduction Reaction Electrocatalytic H2 Oxidation Reaction Electrocatalytic Oxidation of Methanol, Ethanol and Formic Acid Application of First Principles Methods in the Study of Fuel Cell Air-Cathode Electrocatalysis Catalyst Contamination in PEM Fuel Cells PEM Fuel Cell Catalyst Layers and MEAs Catalyst Layer Modeling: Structure, Properties and Performance Catalyst Synthesis Techniques Physical Characterization of Electrocatalysts Electrochemical Methods for Catalyst Activity Evaluation Combinatorial Methods for PEM Fuel Cell Electrocatalysts Platinum-based Alloy Catalysts for PEM Fuel Cells Nanotubes, Nanofibers and Nanowires as Supports for Catalysts Non-noble Electrocatalysts for the PEM Fuel Cell Oxygen Reduction Reaction CO-tolerant Catalysts Reversal-tolerant Catalyst Layers High-temperature PEM Fuel Cell Catalysts and Catalyst Layers Conventional Catalyst Ink, Catalyst Layer and MEA Preparation Spray-based and CVD Processes for Synthesis of Fuel Cell Catalysts and Thin Catalyst Layers Catalyst Layer/MEA Performance Evaluation Catalyst Layer Composition Optimization Catalyst Layer Degradation, Diagnosis and Failure Mitigation

Fischer‐Tropsch Catalysts for the Biomass‐to‐Liquid (BTL)‐Process

Abstract: The Fischer-Tropsch synthesis is at the heart of the Biomass-to-Liquids (BTL) process. Feasibility studies published in open literature typically consider cobalt-based catalysts for the Fischer-Tropsch synthesis. Here, we present an overview on the history and development up until the present for both cobalt- and iron-based Fischer-Tropsch catalysts. The role of the support material and various other additives to the catalyst formulation are discussed in detail with regard to activity, catalyst deactivation, and selectivity. Tentative explanations for e.g. the observed size dependency in cobalt-based catalysts and phase transformations in iron-based Fischer-Tropsch catalysts are offered. The productivity of cobalt-based catalysts at high conversion level is currently higher than that of iron-based catalysts. Nevertheless, it is argued that iron-based catalysts may be an attractive option for the BTL-process, since it is much cheaper, impacting on the cost of the process due to inevitable process set-ups in industrial operation. Improvement of current iron-based catalysts is however desired.

In-situ X-ray Photoelectron Spectroscopy Study of Catalyst−Support Interactions and Growth of Carbon Nanotube Forests

Abstract: We study catalyst support interactions during chemical vapor deposition of carbon nanotubes by in situ X-ray photoelectron spectroscopy over a wide range of pressures. We observe Fe 2+ and 3+ interface states for metallic Fe on Al2O3 in the absence of measurable Al reduction. This support interaction is much stronger than that on SiO2, and it restricts Fe surface mobility. The resulting much narrower Fe catalyst particle size distribution on Al2O3 leads to a higher carbon nanotube nucleation density and a vertical nanotube alignment due to proximity effects. We record the growth kinetics of carbon nanotube forests by optical imaging to understand effects that contribute to growth termination.

Ultra-deep oxidative desulfurization of diesel fuel by the Mo/Al2O3-H2O2 system: The effect of system parameters on catalytic activity

Abstract: This work presents the results obtained in the development of Mo/γ-Al2O3 catalysts and their evaluation in the oxidative desulfurization (OD) process of diesel fuel using hydrogen peroxide as the oxidizing reagent. The catalysts were prepared by equilibrium adsorption using several molybdenum precursors and aluminas with different acidity values. They were characterized by Raman spectroscopy. The effect of the reaction time, reaction temperature, nature of solvent, concentration of solvent and hydrogen peroxide, content of molybdenum and phosphate in the catalysts were investigated. The results showed that the activity for sulfur elimination depends mainly on the presence of hepta- and octamolybdates species on the catalyst support and the use of a polar aprotic solvent. Likewise, the presence of phosphate markedly increases the sulfur elimination. In this way, it is possible to reduce sulfur level in diesel fuel from about 320 to less than 10 ppmw at 333 K and atmospheric pressure. Additionally, on the basis of the results obtained a mechanistic proposal for this reaction is described, as an oxidation mechanism by nucleophilic attack of the sulfur atom on peroxo species of hepta- and octamolybdates, but a mechanism involving the singlet oxygen presence can be discarded.

Application of solid ash based catalysts in heterogeneous catalysis.

Abstract: Solid wastes, fly ash, and bottom ash are generated from coal and biomass combustion. Fly ash is mainly composed of various metal oxides and possesses higher thermal stability. Utilization of fly ash for other industrial applications provides a cost-effective and environmentally friendly way of recycling this solid waste, significantly reducing its environmental effects. On the one hand, due to the higher stability of its major component, aluminosilicates, fly ash could be employed as catalyst support by impregnation of other active components for various reactions. On the other hand, other chemical compounds in fly ash such as Fe2O3 could also provide an active component making fly ash a catalyst for some reactions. In this paper, physicochemical properties of fly ash and its applications for heterogeneous catalysis as a catalyst support or catalyst in a variety of catalytic reactions were reviewed. Fly-ash-supported catalysts have shown good catalytic activities for H2 production, deSOx, deNOx, hydrocar...

Well-dispersed high-loading pt nanoparticles supported by shell-core nanostructured carbon for methanol electrooxidation.

Abstract: Shell−core nanostructured carbon materials with a nitrogen-doped graphitic layer as a shell and pristine carbon black particle as a core were synthesized by carbonizing the hybrid materials containing in situ polymerized aniline onto carbon black. In an N-doped carbon layer, the nitrogen atoms substitute carbon atoms at the edge and interior of the graphene structure to form pyridinic N and quaternary N structures, respectively. As a result, the carbon structure becomes more compact, showing curvatures and disorder in the graphene stacking. In comparison with nondoped carbon, the N-doped one was proved to be a suitable supporting material to synthesize high-loading Pt catalysts (up to 60 wt %) with a more uniform size distribution and stronger metal−support interactions due to its high electrochemically accessible surface area, richness of disorder and defects, and high electron density. Moreover, the more rapid charge-transfer rates over the N-doped carbon material are evidenced by the high crystallinity...

High-performance olefin polymerization catalysts discovered on the basis of a new catalyst design concept

Abstract: This critical review highlights the “ligand oriented catalyst design concept”, a new catalyst design concept for olefin polymerization that has led to the development of high-activity catalysts. The concept has created a series of highly active ethylene polymerization catalysts, many of which show high activities comparable to those of group 4 metallocene catalysts. Moreover, these catalysts display unique polymerization catalysis to produce a wide variety of polymers that possess unprecedented molecular architectures that are either difficult or impossible to achieve using conventional catalysts (98 references).

Hydrogen Evolution on Supported Incomplete Cubane-type (Mo3S4) 4+ Electrocatalysts

Abstract: Electrocatalytic properties of biomimetic supported incomplete cubane-type [Mo3S4]4+ clusters are investigated. The activity toward the hydrogen evolution reaction (HER) is evaluated on both a high surface area gas diffusion electrode in a membrane electrode assembly and on highly orientated pyrolytic graphite (HOPG) supports. Sub-monolayers of the clusters were imaged by means of scanning tunnelling microscopy (STM) prior to electrochemical characterization. This enabled the quantification of the activity on a per cluster basis for the HER and the comparison of the activity with other HER catalysts. We find that the HER activity of the [Mo3S4]4+ is comparable with that of the edge sites of MoS2. The supported [Mo3S4]4+ molecules were also characterized by X-ray photoelectron spectroscopy (XPS), and the observed deterioration in electrocatalytic activity with time was assigned to slow [Mo3S4]4+ cathodic desorption from the catalyst support.

CO2 reforming of CH4 over nanocrystalline zirconia-supported nickel catalysts

Abstract: Mesoporous nanocrystalline zirconia with high-surface area and pure tetragonal crystalline phase has been prepared by the surfactant-assisted route, using Pluronic P123 block copolymer surfactant. The synthesized zirconia showed a surface area of 174 m2 g−1 after calcination at 700 °C for 4 h. The prepared zirconia was employed as a support for nickel catalysts in dry reforming reaction. It was found that these catalysts possessed a mesoporous structure and even high-surface area. The activity results indicated that the nickel catalyst showed stable activity for syngas production with a decrease of about 4% in methane conversion after 50 h of reaction. Addition of promoters (CeO2, La2O3 and K2O) to the catalyst improved both the activity and stability of the nickel catalyst, without any decrease in methane conversion after 50 h of reaction.

Potassium-doped Co3O4 catalyst for direct decomposition of N2O

Abstract: Direct decomposition of nitrous oxide (N 2 O) on K-doped Co 3 O 4 catalysts was examined. The K-doped Co 3 O 4 catalyst showed a high activity even in the presence of water. In the durability test of the K-doped Co 3 O 4 catalyst, the activity was maintained at least for 12 h. It was found that the activity of the K-doped Co 3 O 4 catalyst strongly depended on the amount of K in the catalyst. In order to reveal the role of the K component on the catalytic activity, the catalyst was characterized by XRD, XPS, TPR and TPD. The results suggested that regeneration of the Co 2+ species from the Co 3+ species formed by oxidation of Co 2+ with the oxygen atoms formed by N 2 O decomposition was promoted by the addition of K to the Co 3 O 4 catalyst.

Fischer-Tropsch Synthesis by Carbon Dioxide Hydrogenation on Fe-Based Catalysts

Abstract: Impregnated and co-precipitated, promoted and unpromoted, bulk and supported iron catalysts were prepared, characterized, and subjected to hydrogenation of CO2 at various pressures (1–2 MPa) and temperatures (573–673 K). Potassium, as an important promoter, enhanced the CO2 uptake and selectivity towards olefins and long-chain hydrocarbons. Al2O3, when added as a structural promoter during co-precipitation, increased CO2 conversion as well as selectivity to C2+ hydrocarbons. Among V, Cr, Mn and Zn promoters, Zn offered the highest selectivity to C2–C4 alkenes. The different episodes involved in the transformation of the catalyst before it reached steady-state were identified, on the co-precipitated catalyst. Using a biomass derived syngas (CO/CO2/H2), CO alone took part in hydrogenation. When enriched with H2, CO2 was also converted to hydrocarbons. The deactivation of impregnated Fe–K/Al2O3 catalyst was found to be due to carbon deposition, whereas that for the precipitated catalyst was due to increase in crystallinity of iron species. The suitability of SiO2, TiO2, Al2O3, HY and ion exchanged NaY as supports was examined for obtaining high activity and selectivity towards light olefins and C2+ hydrocarbons and found Al2O3 to be the best support. A comparative study with Co catalysts revealed the advantages of Fe catalysts for hydrocarbon production by F–T synthesis.

Hydrogen production via steam reforming of bio-oil components over calcium aluminate supported nickel and noble metal catalysts

Abstract: Steam reforming of two representative bio-oil components, acetic acid and acetone, was investigated thermally and catalytically over nickel (5 wt%) and noble metal (0.5 wt% Rh or Ir) catalysts supported on calcium aluminates (CaO·2Al2O3 and 12CaO·7Al2O3). The thermal reactions (with or without water) were studied in the presence of inert quartz particles and showed that at 750 °C, acetone and to a lesser extent acetic acid undergo a series of homogeneous reactions forming CO, CO2, CH4 and H2 in concentrations which depend on the organic, and the presence or absence of water. Characteristic of acetone thermal steam reforming is that high amounts of acetic acid are produced. The catalysts prepared were tested at three reaction temperatures 550–650–750 °C using steam/carbon = 3 and space velocities around 30 000 h−1. The results showed that acetic acid is easily reformed over the catalysts to hydrogen rich gas with yield approaching that of equilibrium. Hydrogen yields depend on the metal type and loading and the ratio of CaO to Al2O3 of the support. The best performance in terms of highest hydrogen yield is achieved with the 5 wt% Ni/CaO·2Al2O3 catalyst, while the 0.5 wt% Rh/CaO·2Al2O3 catalyst presents the highest resistant to coking. These catalysts were tested in acetone reforming showing also very high activity, low coking deposition rate and slight superiority of the Rh catalyst in terms of hydrogen yield.

CuO and CeO2 catalysts supported on Al2O3, ZrO2, and SiO2 in the oxidation of CO at low temperature

Abstract: The effect of the support, Al 2 O 3 , ZrO 2 , and SiO 2 , on the activity for CO oxidation of a series of CuO and CeO 2 monometallic and bimetallic catalysts was studied. The catalysts were prepared by coimpregnation of the support with the adequate amount of Cu and Ce nitrates to obtain a loading of 2% Cu and/or 8% Ce. It was found that the support has a strong influence on the activity of the different bimetallic catalysts. Interestingly, the SiO 2 supported catalyst shows the higher activity. The bimetallic supported catalysts follow the activity sequence CuO–CeO 2 /SiO 2 > CuO–CeO 2 /ZrO 2 > CuO–CeO 2 /Al 2 O 3 . In the absence of CeO 2 , the most active monometallic catalyst was the CuO/ZrO 2 system. The different degree of interaction between CuO and CeO 2 particles, induced by the support, can explain the activity results for the bimetallic catalysts.

CNx nanotubes as catalyst support to immobilize platinum nanoparticles for methanol oxidation

Abstract: Pt nanoparticles with sizes of 3–9 nm were well dispersed on carbon nitride (CNx) nanotubes without needing pre-surface modification on the CNx nanotubes due to the inherent chemical activity The products were characterized by transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy All the experimental results revealed that Pt nanoparticles were immobilized on the CNx nanotubes due to the N-participation in the connection of Pt species with the support The electrocatalytic property of the as-prepared Pt/CNx catalyst in methanol oxidation was examined by cyclic voltammetry The results reveal that the so-constructed Pt/CNx catalyst has obvious catalytic activity, suggesting potential applications in fuel cells

Fischer–Tropsch synthesis over cobalt catalyst supported on carbon nanotubes in a slurry reactor

Abstract: The potential of carbon nanotubes (CNTs) supported cobalt catalysts for Fischer–Tropsch (FT) reaction is discussed in this paper. Cobalt on carbon nanotube catalysts were prepared using the wet impregnation method with cobalt loading varying from 15 to 40 wt.%. The catalysts were characterized by BET, X-ray diffraction (XRD), H2 chemisorption, TPR, and transmission electron microscopy (TEM). The activity and selectivity of the catalysts were assessed using a continuous stirred tank reactor (CSTR). Most of the cobalt particles were homogeneously distributed inside the tubes and the rest on the outer of the CNTs. Carbon nanotubes as cobalt catalyst support was found to shift the reduction temperature of cobalt oxide species to lower temperatures. The strong metal–support interactions are reduced to a large extent and the reducibility of the catalysts improved significantly. CNT aided in well dispersion of metal clusters and average cobalt clusters size decreased. The hydrocarbon yield in the FT process obtained by CNT-supported cobalt catalyst is about 75% more than that obtained using cobalt on alumina supports. The maximum concentration of active surface Co° sites and FTS activity for CNT-supported catalysts are achieved at 40 wt.% cobalt loading. CNT caused a slight decrease in FTS product distribution to lower molecular weight hydrocarbons.

Layered Double Hydroxides as Catalytic Materials: Recent Development

Abstract: This report surveys the recent development of layered double hydroxides (LDHs) as catalytic materials, which have attracted considerable attention in the past decade. A major challenge in the rapidly growing field is to improve the functionalities of these materials. Therefore, this article is mainly focused on the lately reported design and synthesis strategies for LDH materials and their catalytic applications as actual catalysts, catalyst precursors and catalyst supports.