Showing papers on "Catalyst support published in 2012"

Catalyst–support interactions: Electronic perturbations

Abstract: Oxide materials typically used as supports for the active metal nanoparticles of heterogeneous catalysts are known to influence catalytic activity through strong metal–support interactions. Researchers have now revealed electronic interactions between platinum and ceria that go well beyond known effects and lead to excellent catalytic activity.

Graphene as a new carbon support for low-temperature fuel cell catalysts

Abstract: Highly dispersed catalysts on a conductive support, commonly platinum and platinum-based catalysts, are used as electrode materials in low-temperature fuel cells. Carbon blacks are commonly used as fuel cell catalysts supports, but their properties are not completely satisfactory. Thus, in the last years carbon black alternative materials such as nanostructured carbons, ceramic and polymer materials have been proposed as fuel cell catalyst supports. Very recently, in consideration of their high surface area, high conductivity, unique graphitized basal plane structure and potential low manufacturing cost, graphene nanosheets have been investigated as a support for low-temperature fuel cell catalysts. This paper presents an overview of graphene nanosheets used as supports for fuel cell catalysts. In particular, the catalytic activity and durability of catalysts supported on graphene are compared with those of catalysts supported on the commonly used carbon blacks and on carbon nanotubes, that is, on rolled graphene.

Mesoporous g-C3N4 nanorods as multifunctional supports of ultrafine metal nanoparticles: hydrogen generation from water and reduction of nitrophenol with tandem catalysis in one step

Abstract: Flexible mesoporous g-C3N4 nanorods with open channels, synthesized via nanocasting, can act as catalyst support, solid stabilizer and photosensitizer simultaneously for anchoring uniform metal nanoparticles with high compatibility with the composition, the synthetic method and the particle size. The final hybrid nanorods exhibit high stability and catalytic/photocatalytic activity.

Electro-Fenton oxidation of pesticides with a novel Fe3O4@Fe2O3/activated carbon aerogel cathode: High activity, wide pH range and catalytic mechanism

Abstract: A novel electro-Fenton (E-Fenton) system with the Fe3O4@Fe2O3/activated carbon aerogel (ACA) composite cathode was firstly constructed in this study. Its application on degrading imidacloprid exhibited highly catalytic efficiency over a wide applicable pH range from 3 to 9. The removal of imidacloprid and TOC achieved to 90% within 30 and 60 min, respectively. The nature of composite cathode was examined by BJH, XRD, SEM, TEM, XPS and FTIR techniques. ACA with high surface area of 2410 m2 g−1 and multiplicated porosities composed of micropores and mesopores worked not only as cathode but also as Fenton catalyst support, enhancing oxidation activity. We proposed reasonable E-Fenton oxidation mechanisms with Fe3O4@Fe2O3/ACA cathode at acidic and basic conditions. At pH 3, it followed a Haber–Weiss mechanism that the dissolved iron ions and surface Fe(II) sites catalyzed the decomposition of H2O2 to generate hydroxyl radicals ( OH). While at pH 9, it was expected the formation and deactivation of H2O2 complex as well as the catalytic decomposition of H2O2 with surface Fe(III) and Fe(II) sites to produce both superoxide anion ( O2−/HO2 ) and hydroxyl radicals ( OH), involving an in situ recycling of iron oxide (FeO·Fe2O3 → Fe2O3).

A heterogeneous nickel catalyst for the hydrogenolysis of aryl ethers without arene hydrogenation.

Abstract: A heterogeneous nickel catalyst for the selective hydrogenolysis of aryl ethers to arenes and alcohols generated without an added dative ligand is described. The catalyst is formed in situ from the...

Dry Reforming of Methane Over Cobalt Catalysts: A Literature Review of Catalyst Development

Abstract: Dry reforming of methane produces syngas with desirable H2/CO ratio. Besides noble metal catalysts, the cobalt catalyst performs good activity in this reaction. However, carbon deposition and catalyst deactivation are becoming the main problems inhibiting the scale up of this process into industrial application. Recently, many scientists were trying to increase the activity as well as the stability toward coking by using variants of support, promoter, and combination of metal series catalyst. This paper presents a recent technology of methane dry reforming over cobalt metal-base catalyst, covering the catalyst activity and their resistance of catalyst deactivation.

Efficient magnesium catalysts for the copolymerization of epoxides and CO2; using water to synthesize polycarbonate polyols.

Abstract: The synthesis and characterization of three highly active dimagnesium catalysts for the copolymerization of cyclohexene oxide and carbon dioxide, active under just 1 atm of carbon dioxide pressure, are reported. The catalysts have turnover numbers up to 6000 and turnover frequencies of up to 750 h–1. These values are, respectively, 75 and 20 times higher than those of the other three known magnesium catalysts. Furthermore, the catalysts operate at 1/500th the loading of the best reported magnesium catalyst. The catalyst selectivities are excellent, yielding polymers with 99% carbonate repeat units and >99% selectivity for copolymer. Using a dimagnesium bis(trifluoroacetate) catalyst, and water as a renewable chain transfer reagent, poly(cyclohexene carbonate) polyols are synthesized with high selectivity.

Novel Platinum–Cobalt Alloy Nanoparticles Dispersed on Nitrogen-Doped Graphene as a Cathode Electrocatalyst for PEMFC Applications

Abstract: A novel synthesis procedure is devised to obtain nitrogen-doping in hydrogen-exfoliated graphene (HEG) sheets. An anionic polyelectrolyte–conducting polymer duo is used to form a uniform coating of the polymer over graphene sheets. Pyrolysis of graphene coated with polypyrrole, a nitrogen-containing polymer, in an inert environment leads to the incorporation of nitrogen atoms in the graphene network with simultaneous removal of the polymer. These nitrogen-doped graphene (N-HEG) sheets are used as catalyst support for dispersing platinum and platinum–cobalt alloy nanoparticles synthesized by the modified-polyol reduction method, yielding a uniform dispersion of the catalyst nanoparticles. Compared to commercial Pt/C electrocatalyst, Pt–Co/N-HEG cathode electrocatalyst exhibits four times higher power density in proton exchange membrane fuel cells, which is attributed to the excellent dispersion of Pt–Co alloy nanoparticles on the N-HEG support, the alloying effect of Pt–Co, and the high electrocatalytic activity of the N-HEG support. A stability study shows that Pt/N-HEG and Pt–Co/N-HEG cathode electrocatalysts are highly stable in acidic media. The study shows two promising electrocatalysts for proton exchange membrane fuel cells, which on the basis of performance and stability present the possibility of replacing contemporary electrocatalysts.

Design strategies for the molecular level synthesis of supported catalysts.

Abstract: Supported catalysts, metal or oxide catalytic centers constructed on an underlying solid phase, are making an increasingly important contribution to heterogeneous catalysis. For example, in industry, supported catalysts are employed in selective oxidation, selective reduction, and polymerization reactions. Supported structures increase the thermal stability, dispersion, and surface area of the catalyst relative to the neat catalytic material. However, structural and mechanistic characterization of these catalysts presents a formidable challenge because traditional preparations typically afford complex mixtures of structures whose individual components cannot be isolated. As a result, the characterization of supported catalysts requires a combination of advanced spectroscopies for their characterization, unlike homogeneous catalysts, which have relatively uniform structures and can often be characterized using standard methods. Moreover, these advanced spectroscopic techniques only provide ensemble average...

Rhodium-nickel nanoparticles grown on graphene as highly efficient catalyst for complete decomposition of hydrous hydrazine at room temperature for chemical hydrogen storage

Abstract: Well-dispersed rhodium–nickel nanoparticles grown on graphene are successfully synthesized by co-reduction of graphene oxide and metal precursors, wherein graphene proved to be a powerful dispersion agent and distinct support for the RhNi nanoparticles. Unexpectedly, the resultant RhNi@graphene catalyst exerts 100% selectively and exceedingly high activity to complete the decomposition reaction of hydrous hydrazine at room temperature. This excellent catalytic performance might be due to the synergistic effect of the graphene support and the RhNi nanoparticles and the promotion effect of NaOH. The utilization of graphene as a novel two-dimensional catalyst support to anchor active component nanoparticles and thus to facilitate the electron transfer and mass transport kinetics during the catalytic reaction process opens up new avenues for designing next-generation catalysts.

Direct Amidation of Carboxylic Acids Catalyzed by ortho-Iodo Arylboronic Acids: Catalyst Optimization, Scope, and Preliminary Mechanistic Study Supporting a Peculiar Halogen Acceleration Effect

Abstract: The importance of amides as a component of biomolecules and synthetic products motivates the development of catalytic, direct amidation methods employing free carboxylic acids and amines that circumvent the need for stoichiometric activation or coupling reagents. ortho-Iodophenylboronic acid 4a has recently been shown to catalyze direct amidation reactions at room temperature in the presence of 4A molecular sieves as dehydrating agent. Herein, the arene core of ortho-iodoarylboronic acid catalysts has been optimized with regards to the electronic effects of ring substitution. Contrary to the expectation, it was found that electron-donating substituents are preferable, in particular, an alkoxy substituent positioned para to the iodide. The optimal new catalyst, 5-methoxy-2-iodophenylboronic acid (MIBA, 4f), was demonstrated to be kinetically more active than the parent des-methoxy catalyst 4a, providing higher yields of amide products in shorter reaction times under mild conditions at ambient temperature. ...

Poly(ionic liquid) Complex with Spontaneous Micro-/Mesoporosity: Template-Free Synthesis and Application as Catalyst Support

Abstract: A facile, template-free synthetic route is reported toward poly(ionic liquid) complexes (PILCs) which for the first time exhibit stable micro-/mesoporous structure. This is accomplished via in situ ionic complexation between imidazolium-based PILs and poly(acrylic acid) in various alkaline organic solvents. The PILC can be highly loaded with copper salts and can be used as a catalytic support for effective aerobic oxidation of activated hydrocarbons under mild conditions.

Nitrogen‐Doped Carbon Nanotubes as a Highly Active Metal‐Free Catalyst for Selective Oxidation

Abstract: Catalytic reactions are generally carried out on supported metals or oxides, which act as an active phase and require impregnation and thermal treatment steps. During tests, the metal or oxide nanoparticles could be further sintered, which would induces deactivation. Direct incorporation of the active phase into the matrix of a support could be an elegant alternative to prevent catalyst deactivation. Here, we report that nitrogen-doped carbon nanotubes (N-CNTs) can be efficiently employed as a metal-free catalyst for oxidative reactions that allow the selective transformation of the harmful, gaseous H(2)S into solid sulfur. The catalyst exhibits a high stability during the test at high space velocity. The macroscopic shaping of the catalyst on the silicon carbide foam also increases its catalytic activity by improving the contact between the reactants and the catalyst. Such macroscopic shaping allows the avoidance of problems linked with transport and handling of nanoscopic materials and also reduces the pressure drop across the catalyst bed to a large extent.

Nanoporous surface alloys as highly active and durable oxygen reduction reaction electrocatalysts

Abstract: It is of critical importance to design and fabricate highly active and durable oxygen reduction reaction (ORR) catalysts for the application of proton exchange membrane fuel cells (PEMFCs). By a simple two-step dealloying process, the active components in a Pt/Ni/Al ternary alloy were sequentially leached out in a highly controllable manner, generating a novel nanoporous surface alloy structure. Characterized by an open bicontinuous spongy morphology, the resulting nanostructure is interconnected by ∼3 nm diameter ligaments which are comprised of a Pt/Ni alloy core and a nearly pure Pt surface. In the absence of any catalyst support, these nanoporous surface alloys show much enhanced durability and electrocatalytic activity for ORR as compared to the commercial Pt/C catalyst. At a high potential, such as 0.9 V versusRHE, nanoporous Pt/Ni surface alloys show a remarkable specific activity of 1.23 mA cm−2. These nanomaterials thus hold great potential as cathode catalysts in PEMFCs in terms of facile preparation, clean catalyst surface, and enhanced ORR activity and durability.

Multi-Layer Functionalized Poly(Ionic Liquid) Coated Magnetic Nanoparticles: Highly Recoverable and Magnetically Separable Brønsted Acid Catalyst

Abstract: A functionalized poly(ionic liquid) coated magnetic nanoparticle (Fe3O4@PIL) catalyst was successfully synthesized by polymerization of functionalized vinylimidazolium in the presence of surface modified magnetic nanoparticles. The resulting heterogeneous catalyst is shown to be an efficient acidic catalyst for synthesis of 1,1-diacetyl from aldehydes under solvent free conditions and room temperature in high yields. Also, the catalyst shows good activity for the deprotection reaction of acylals. After completion of reaction, the catalyst was simply recovered by an external conventional magnet and recycled without significant loss in the catalytic activity. Because of the polymer layers coated surface of the magnetic nanoparticles, the catalyst has a good thermal stability and recyclability. The poly(ionic liquid) coated magnetic nanoparticles represents a novel class of heterogeneous catalyst which are particularly attractive in the practice of organic synthesis in an environmentally friendly manner.

Recent advances in the selective catalytic reduction of NOx by hydrogen in the presence of oxygen

Abstract: Selective catalytic reduction of NOx by hydrogen (H2-SCR) in the presence of oxygen has received much attention as a potential technology for reducing NOx emissions. A lot of research has been done in order to understand the reaction mechanism of H2-SCR and some possible mechanisms have been proposed. These mechanisms can be classified into two categories: NO adsorption/dissociation mechanisms and oxidation–reduction mechanisms. Based on the discussion of the reaction mechanism, the influence of the nature of the noble metal, catalyst support, catalyst preparation method, promoters and reaction conditions (including the presence of H2 and O2, water, sulfur, CO and CO2) on the catalytic performance of some H2-SCR catalysts has been discussed. Finally, future research directions in the area of H2-SCR have been proposed.

Heterogeneous catalysts for production of chemicals using carbon dioxide as raw material: A review

Abstract: The utilization of CO2 for the production of useful chemicals using heterogeneous catalysts is one of the ways to reduce the anthropogenic greenhouse gases in the atmosphere. In many cases, the CO2 conversion and products yield are still considered very low and need to be operated at high pressure and temperature. The critical point in CO2 conversion is to activate the CO2 molecules either by adding a co-reactant or by using effective catalysts. This paper presents the current development on the effect of several precursors like metals, metal oxides, ionic liquids, and acid–base loaded on a suitable support in creating magical properties of catalysts on the performance of CO2 conversion. Cu/ZnO-based catalysts, ionic liquid-based catalysts, and metal oxides-based catalysts are reported to be the most effective catalysts in the formation of methanol, cyclic carbonates and dimethyl carbonate. This review also focuses on various strategies and developments in altering heterogeneous catalysts, followed by critical factors of CO2 molecule activation, and the optimization of the catalytic activity or catalysts reusability.

Perovskite Sr0.95Ce0.05CoO3-delta loaded with copper nanoparticles as a bifunctional catalyst for lithium-air batteries

Abstract: Sr0.95Ce0.05CoO3−δ (SCCO) particles loaded with copper nanoparticles on their surface are shown to be excellent, low-cost, and stable bifunctional catalysts for the oxygen-reduction and oxygen-evolution reactions (ORR and OER) in aqueous solution. Evidence for the presence of Ce3+ and Co2+ as well as Co4+ and Co3+ ions revealed by XPS measurements as well as XRD analysis indicates that a CeCoO2.5 brownmillerite phase may be extruded to the surface. A surface Co4+/Co3+ couple is known to be a good OER catalyst. The performance of the SCCO-based catalysts is better at higher current rates (>0.1 mA cm−2) than that of Vulcan XC-72 and even close to that of the 50% Pt/carbon-black catalyst. This catalyst could be used in a metal/air battery or a PEM fuel cell as an efficient and stable bifunctional catalyst.

Hydrotreating of Jatropha Oil over Alumina Based Catalysts

Abstract: Hydrotreatment of nonedible jatropha oils over PtPd/Al2O3 catalyst and NiMoP/Al2O3 catalysts was investigated under conditions of 330–390 °C, 3 MPa and 2 h–1 in a fixed-bed reactor. A significantly high yield range of about 82 wt % of liquid hydrocarbon products was achieved over all catalysts. Moreover, the liquid hydrocarbon products have low acid number, suitable density and viscosity, and quite high cetane index. The oil can be a high-performance additive for diesel oil. The oxygen removal pathway of jatropha oil over PtPd/Al2O3 catalyst is primarily compiled through decarboxylation and/or decarbonylation, but over NiMoP/Al2O3 catalysts, the oxygen removal pathways are executed primarily by hydro-deoxygenation. A long-term experiment was conducted over catalyst A (NiMoP/Al2O3). Results show that catalyst A starts deactivation from reaction time of 120 h. The sulfide catalyst conversion to oxide catalyst is regarded as the main reason for deactivation. The deactivated catalyst can be reused after regen...

Hydrodeoxygenation of guaiacol over carbon-supported molybdenum nitride catalysts: Effects of nitriding methods and support properties

Abstract: Molybdenum nitride catalysts supported on activated carbon materials with different textural and chemical properties were synthesized by nitriding supported Mo oxide precursors with gaseous NH 3 or N 2 /H 2 mixtures using a temperature-programmed reaction. The supports and catalysts were characterized by N 2 physisorption, XRD, chemical analysis, TPD, FT-IR and XPS. Guaiacol (2-methoxyphenol) hydrodeoxygenation (HDO) activities at 5 MPa and 300 °C were evaluated in a batch autoclave reactor. Molybdenum nitrides prepared using a N 2 /H 2 mixture resulted in more highly dispersed catalysts, and consequently more active catalysts, relative to those prepared using ammonolysis. The HDO activity was also related to pore size distribution and the concentration of oxygen-containing surface groups of the different carbon supports. Increased mesoporosity is argued to have facilitated the access to active sites while increased surface acidity enhanced their catalytic activity through modification of their electronic properties. The highest activity was thus attributed to the highest dispersion of the unsaturated catalyst species and the highest support mesoporosity. Surprisingly, addition of Co did not improve the HDO activity.

CO2 methanation on Rh/γ-Al2O3 catalyst at low temperature: “In situ” supply of hydrogen by Ni/activated carbon catalyst

Abstract: Nowadays, the control of CO2 emissions is still a challenge. A few alternatives exist but nothing concrete seems to be developed. Instead of catching and storing CO2, one possibility would be its transformation into value added molecules as methane. Rhodium catalysts are active in CO2 methanation reaction. But it seems that a competitive adsorption exist between the two reactants: CO2 and hydrogen. In order to surpass this trouble and increase hydrogen adsorption, a known active catalyst in methanation (Rh/γ-Al2O3) was put into contact with a known active catalyst in hydrogen activation (Ni/activated carbon). Catalysts were prepared by the mechanical mixing of the latter two in different proportions. Catalysts were tested in the low temperature methanation reaction using CO2 and H2. Methane is produced in all cases with a 100% of selectivity. A significant synergy appears in the catalytic activity of this mixed catalyst. Production of methane in mixtures is largely higher than the theoretical predicted values considering the individual performances. Catalysts were characterized before and after reaction by ICP-AES, N2 physisorption, XRD, CO2 chemisorption, ToF-SIMS, XPS and TPR. The synergy is due to the increase of H2 adsorption and promoting the carbon hydride formation. Furthermore the suggested hydrogen spill-over maintains Rh particles in a metallic state necessary for the reaction.

One-Pot Liquid-Phase Catalytic Conversion of Ethanol to 1-Butanol over Aluminium Oxide—The Effect of the Active Metal on the Selectivity

Abstract: Direct catalytic valorization of bioethanol to 1-butanol over different alumina supported catalysts was studied. Thirteen (13) heterogeneous catalysts were screened in search for the optimal material composition for direct one-pot conversion of ethanol to 1-butanol. For the most promising catalyst, a 25% ethanol conversion with 80% selectivity (among liquid carbon products) to 1-butanol could be reached at 250 °C. Additionally, the reaction kinetics and mechanisms were further investigated upon use of the most suitable catalyst candidate.