Showing papers on "Catalyst support published in 2013"

Towards stable catalysts by controlling collective properties of supported metal nanoparticles

Abstract: Supported metal nanoparticles play a pivotal role in areas such as nanoelectronics, energy storage/conversion and as catalysts for the sustainable production of fuels and chemicals. However, the tendency of nanoparticles to grow into larger crystallites is an impediment for stable performance. Exemplarily, loss of active surface area by metal particle growth is a major cause of deactivation for supported catalysts. In specific cases particle growth might be mitigated by tuning the properties of individual nanoparticles, such as size, composition and interaction with the support. Here we present an alternative strategy based on control over collective properties, revealing the pronounced impact of the three-dimensional nanospatial distribution of metal particles on catalyst stability. We employ silica-supported copper nanoparticles as catalysts for methanol synthesis as a showcase. Achieving near-maximum interparticle spacings, as accessed quantitatively by electron tomography, slows down deactivation up to an order of magnitude compared with a catalyst with a non-uniform nanoparticle distribution, or a reference Cu/ZnO/Al(2)O(3) catalyst. Our approach paves the way towards the rational design of practically relevant catalysts and other nanomaterials with enhanced stability and functionality, for applications such as sensors, gas storage, batteries and solar fuel production.

High Performance Fe- and N- Doped Carbon Catalyst with Graphene Structure for Oxygen Reduction

Abstract: High Performance Fe- and N- Doped Carbon Catalyst with Graphene Structure for Oxygen Reduction

Catalytic Aminohalogenation of Alkenes and Alkynes.

Abstract: Transition metal carbides (TMCs) have attracted a significant amount of attention over the past few years as electrocatalyst support materials. TMCs are interesting because of their similar electronic structures to noble metals near the Fermi level (i.e., WC and Pt), which can promote electron transfer between the catalyst and its support—to enhance the stability of supported Pt nanoparticles as well as enhance its intrinsic activity for select reactions. This perspective article summarizes both theoretical and experimental results for Pt catalysts supported by TMCs for hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) to explore the interaction mechanism of the catalysts and the carbide supports. The strategies to improve the present carbide supports for HER and ORR are also discussed, which is expected to shed light on future development of TMC electrocatalyst supports.

Core-shell Fe3O4 polydopamine nanoparticles serve multipurpose as drug carrier, catalyst support and carbon adsorbent.

Abstract: We present the synthesis and multifunctional utilization of core-shell Fe3O4 polydopamine nanoparticles (Fe3O4@PDA NPs) to serve as the enabling platform for a range of applications including responsive drug delivery, recyclable catalyst support, and adsorbent. Magnetite Fe3O4 NPs formed in a one-pot process by the hydrothermal approach were coated with a polydopamine shell layer of ~20 nm in thickness. The as prepared Fe3O4@PDA NPs were used for the controlled drug release in a pH-sensitive manner via reversible bonding between catechol and boronic acid groups of PDA and the anticancer drug bortezomib (BTZ), respectively. The facile deposition of Au NPs atop Fe3O4@PDA NPs was achieved by utilizing PDA as both the reducing agent and the coupling agent. The nanocatalysts exhibited high catalytic performance for the reduction of o-nitrophenol. Furthermore, the recovery and reuse of the catalyst was demonstrated 10 times without any detectible loss in activity. Finally, the PDA layers were converted into carbon to obtain Fe3O4@C and used as an adsorbent for the removal of Rhodamine B from an aqueous solution. The synergistic combination of unique features of PDA and magnetic nanoparticles establishes these core-shell NPs as a versatile platform for multiple applications.

Biomass-derived electrocatalytic composites for hydrogen evolution

Abstract: The production of hydrogen from water electrolysis calls for an efficient non-precious-metal catalyst to make the process economically viable because of the high cost and the limited supply of the currently used platinum catalysts. Here we present such a catalyst made from earth-abundant molybdenum and common, humble soybeans (MoSoy). This catalyst, composed of a catalytic β-Mo2C phase and an acid-proof γ-Mo2N phase, drives the hydrogen evolution reaction (HER) with low overpotentials, and is highly durable in a corrosive acidic solution over a period exceeding 500 hours. When supported on graphene sheets, the MoSoy catalyst exhibits very fast charge transfer kinetics, and its performance rivals that of noble-metal catalysts such as Pt for hydrogen production. These findings prove that the soybean (as well as other high-protein biomass) is a useful material for the generation of catalysts incorporating an abundant transition metal, thereby challenging the exclusivity of platinum catalysts in the hydrogen economy.

Oxidative Dehydrogenation on Nanocarbon: Identification and Quantification of Active Sites by Chemical Titration

Abstract: Nanostructured carbon-based materials have shown high catalytic activity in several important reactions and related chemical industrial processes, such as direct or oxidative dehydrogenation of hydrocarbons and Friedel–Crafts reactions. Nanocarbon materials exhibit significant advantages over traditional metal or metal oxide based catalysts because of their tunable acidity/basicity, electron density, and convenient recycling and reusability, and they have been shown to be potential alternatives to conventional catalysts to meet the requirements of sustainable chemistry. As a result, the field of nanocarbon catalysis has been experiencing an unparalleled development of new catalyst synthesis or their applications in new reaction systems. However, there is only slow growth of mechanistic interpretation of carbon-catalyzed reactions, which is even more urgent to advance our knowledge in related fields. Present research on the mechanism of carbon catalysis suggests that oxygen containing functional groups, especially ketonic carbonyl groups on nanocarbon, which are rich in electrons, may act as the catalytic active sites for oxidative dehydrogenation (ODH) of alkanes to corresponding alkenes. The reaction process is assumed to be similar to that for transition-metal oxide catalysts. The C H bonds of alkanes dissociate at active oxygen functional groups, and the hydrogen atoms are abstracted by Lewis base sites. After the desorption of alkene products, gas-phase O2 reacts with the abstracted hydrogen to form H2O, then the active catalytic sites are regenerated to finish one catalytic cycle. The above unspecific catalytic mechanism is only based on the qualitative characterization of carbon catalysts, while the identity of the active sites or a detailed kinetic study has never been executed with direct and convincing chemical evidence. One of the most critical problems that limits the quantitative description of the catalytic mechanism is the uncertainty of the chemical structure of nanocarbon materials. The coexistence of several kinds of surface functional groups (such as hydroxyl, carbonyl, and carboxylic acid groups) is unavoidable, as the synthesis or the following surface modification procedures of nanocarbon catalysts are normally realized by a severe physical or chemical process, such as laser irradiation and oxidation by HNO3, O2, and O3. [8] There are still lack of reliable quantification methods for the surface functional groups on nanostructured carbon materials because of their complexity in type and quantity. As a result, turnover frequency (TOF), the ultimate parameter to evaluate the intrinsic activity of heterogeneous catalysts, is also rarely reported in the case of nanocarbon catalysts, making it impossible to study the detailed reaction kinetics or compare the activity of carbon catalysts bearing different structures fairly and objectively. The quantitative surface composition analysis is also desirable for the application of nanostructured carbon as a catalyst support or electrochemical devices, which takes an even larger proportion in the field of carbon materials, as the surface structure of nanocarbon materials is essential for their physical or chemical properties (for example, affinity for a certain metal or metal ion). In view of the quantification methods of oxygen functional groups, herein we propose a chemical titration method to determine the surface concentration of three kinds of typical oxygen functional groups ( C=O, C OH, and COOH) on the surface of carbon nanotubes (CNTs) (Scheme 1). Through selective deactivation of these specific oxygen functional groups and the assessment of the catalytic activity of different CNT derivatives for ethylbenzene (EB) ODH reactions, we provided chemical evidence to show that

Ammonia synthesis catalysts : innovation and practice

Abstract: Development of Ammonia Synthesis Catalysts Catalytic Reaction Mechanism For Ammonia Synthesis Chemical Composition and Structure of Fused Iron Catalysts Preparation of Iron Catalysts Reduction of Fused Iron Catalyst Ruthenium Catalysts Performance Evaluation and Characterization of Catalysts Performance and Application of Catalysts Effect of Catalysts Performance On Economic Benefit of Catalytic Process Outlook and Innovation.

SBA-15 Mesoporous Silica as Catalytic Support for Hydrodesulfurization Catalysts-Review.

Abstract: SBA-15 is an interesting mesoporous silica material having highly ordered nanopores and a large surface area, which is widely employed as catalyst supports, absorbents, drug delivery materials, etc. Since it has a lack of functionality, heteroatoms and organic functional groups have been incorporated by direct or post-synthesis methods in order to modify their functionality. The aim of this article is to review the state-of-the-art related to the use of SBA-15-based mesoporous systems as supports for hydrodesulfurization (HDS) catalysts.

Heterogeneous Ni Catalyst for Direct Synthesis of Primary Amines from Alcohols and Ammonia

Abstract: This paper reports the synthesis of primary amines from alcohols and NH3 by an Al2O3-supported Ni nanoparticle catalyst as the first example of heterogeneous and noble-metal-free catalytic system for this reaction without additional hydrogen sources under relatively mild conditions. Various aliphatic alcohols are tolerated, and turnover numbers were higher than those of Ru-based homogeneous catalysts. The catalyst was recoverable and was reused. The effects of the Ni oxidation states and the acid–base nature of support oxides on the catalytic activity are studied. It is clarified that the surface metallic Ni sites are the catalytically active species, and the copresence of acidic and basic sites on the support surface is also indispensable for this catalytic system.

Application of heterogeneous catalysts prepared by mechanochemical synthesis.

Abstract: Mechanochemical synthesis has the potential to provide more sustainable preparative routes to catalysts than the current multistep solvent-based routes. In this review, the mechanochemical synthesis of catalysts is discussed, with emphasis placed on catalysts for environmental, energy and chemical synthesis applications. This includes the formation of mixed-metal oxides as well as the process of dispersing metals onto solid supports. In most cases the process involves no solvent. Encouragingly, there are several examples where the process is advantageous compared with the more normal solvent-based methods. This can be because of process cost or simplicity, or, notably, where it provides more active/selective catalysts than those made by conventional wet chemical methods. The need for greater, and more systematic, exploration of this currently unconventional approach to catalyst synthesis is highlighted.

Stabilization of copper catalysts for liquid-phase reactions by atomic layer deposition.

Abstract: Atomic layer deposition (ALD) of an alumina overcoat can stabilize a base metal catalyst (e.g., copper) for liquid-phase catalytic reactions (e.g., hydrogenation of biomass-derived furfural in alcoholic solvents or water), thereby eliminating the deactivation of conventional catalysts by sintering and leaching. This method of catalyst stabilization alleviates the need to employ precious metals (e.g., platinum) in liquid-phase catalytic processing. The alumina overcoat initially covers the catalyst surface completely. By using solid state NMR spectroscopy, X-ray diffraction, and electron microscopy, it was shown that high temperature treatment opens porosity in the overcoat by forming crystallites of γ-Al2O3. Infrared spectroscopic measurements and scanning tunneling microscopy studies of trimethylaluminum ALD on copper show that the remarkable stability imparted to the nanoparticles arises from selective armoring of under-coordinated copper atoms on the nanoparticle surface.

Use of polypyrrole in catalysts for low temperature fuel cells

Abstract: Carbon materials, especially Vulcan XC-72 carbon black, are the most widely used catalyst support in low temperature fuel cells. Several disadvantages of these catalyst supports, however, limit the catalyst performance leading to reduced fuel cell performance and durability: low resistance to corrosion at high potentials, micropores leading to limited accessible surface, impermeability to gases and liquids, and no proton conductivity. Therefore, development of novel supports or modified carbon materials is essential to commercialization of low temperature fuel cell technology. Due to unique metallic/semiconductor characteristics along with excellent environmental stability, facile synthesis and high conductivity, polypyrrole (PPy), a member of the conjugated heterocyclic conducting polymers, has been considered the most promising alternative to carbon supports in fuel cells. Extensive research on PPy-containing catalysts has been reported in the last twenty years. This paper systematically and critically reviews the progress and main achievements of PPy use in both anode and cathode catalysts for low temperature fuel cells. Insight into the remaining challenges and future research directions is also discussed.

Platinum–TM (TM = Fe, Co) alloy nanoparticles dispersed nitrogen doped (reduced graphene oxide-multiwalled carbon nanotube) hybrid structure cathode electrocatalysts for high performance PEMFC applications

Abstract: The efforts to push proton exchange membrane fuel cells (PEMFC) for commercial applications are being undertaken globally. In PEMFC, the sluggish kinetics of oxygen reduction reactions (ORR) at the cathode can be improved by the alloying of platinum with 3d-transition metals (TM = Fe, Co, etc.) and with nitrogen doping, and in the present work we have combined both of these aspects. We describe a facile method for the synthesis of a nitrogen doped (reduced graphene oxide (rGO)–multiwalled carbon nanotubes (MWNTs)) hybrid structure (N–(G–MWNTs)) by the uniform coating of a nitrogen containing polymer over the surface of the hybrid structure (positively surface charged rGO–negatively surface charged MWNTs) followed by the pyrolysis of these (rGO–MWNTs) hybrid structure–polymer composites. The N–(G–MWNTs) hybrid structure is used as a catalyst support for the dispersion of platinum (Pt), platinum–iron (Pt3Fe) and platinum–cobalt (Pt3Co) alloy nanoparticles. The PEMFC performances of Pt–TM alloy nanoparticle dispersed N–(G–MWNTs) hybrid structure electrocatalysts are 5.0 times higher than that of commercial Pt–C electrocatalysts along with very good stability under acidic environment conditions. This work demonstrates a considerable improvement in performance compared to existing cathode electrocatalysts being used in PEMFC and can be extended to the synthesis of metal, metal oxides or metal alloy nanoparticle decorated nitrogen doped carbon nanostructures for various electrochemical energy applications.

Particle size and support effects in electrocatalysis.

Abstract: Researchers increasingly recognize that, as with standard supportedheterogeneous catalysts, the activity and selectivity of supported metal electrocatalysts are influenced by particle size, particle structure, and catalyst support. Studies using model supported heterogeneous catalysts have provided information about these effects. Similarly, model electrochemical studies on supported metal electrocatalysts can provide insight into the factors determining catalytic activity. High-throughput methods for catalyst synthesis and screening candetermine systematic trends in activity as a function of support and particle size with excellent statistical certainty. In this Account, we describe several such studies investigating methods for dispersing precious metals on both carbon and oxide supports, with particular emphasis on the prospects for the development of low-temperature fuel-cell electrocatalysts. One key finding is a decrease in catalytic activity with decreasing particle size independent of the support for both oxygen reduction and CO oxidation on supported gold and platinum. For these reactions, there appears to be an intrinsic particle size effect that results in a loss of activity at particle sizes below 2–3 nm. A titania support, however, also increases activity of gold particles in the electrooxidation of CO and in the reduction of oxygen, with an optimum at 3 nm particle size. This optimum may represent the superposition of competing effects: a titania-induced enhanced activity versus deactivation at small particle sizes. The titania support shows catalytic activity at potentials where carbon-supported and bulk-gold surfaces are normally oxidized and CO electrooxidation is poisoned. On the other hand, platinum on amorphous titania shows a different effect: the oxidation reduction reaction is strongly poisoned in the same particle size range. We correlated the influence of the titania support with titania-induced changes in the surface redox behavior of the platinum particles. For both supported gold and platinum particles in electrocatalysis, we observe parallels to the effects of particle size and support in the equivalent heterogeneous catalysts. Studies of model supported-metal electrocatalysts, performs efficiently using high throughput synthetic and screening methodologies, will lead to a better understanding of the mechanisms responsible for support and particle size effects in electrocatalysis, and will drive the development of more effective and robust catalysts in the future

Highly Selective Synthesis of Phenol from Benzene over a Vanadium‐Doped Graphitic Carbon Nitride Catalyst

Abstract: Design and preparation of efficient and economical catalysts for direct hydroxylation of benzene to phenol is an important topic. In this work, a series of metal-doped graphitic carbon nitride catalyst (Cu-, Fe-, V-, Co-, and Ni-g-C3N4) were successfully synthesized by using urea as the precursor through a facile and efficient method. The catalysts were characterized systematically using N2 adsorption–desorption, FTIR, thermogravimetric analysis, powder X-ray diffraction, and X-ray photoelectron spectroscopy techniques. It was found that the vanadium-doped graphitic carbon nitride catalyst V-g-C3N4 was the most efficient catalyst for the direct synthesis of phenol from benzene with hydrogen peroxide as the oxidant and it could be recycled at least 4 times. The influence of reaction conditions such as the solvent, reaction temperature, reaction time, and the amounts of catalyst and hydrogen peroxide were investigated. Under optimized conditions, 18.2 % yield of phenol was obtained with the selectivity to phenol as high as 100 %.

How to Prepare a Good Cu/ZnO Catalyst or the Role of Solid State Chemistry for the Synthesis of Nanostructured Catalysts

Abstract: In this research report we summarize recent progress that has been made in the field of Cu/ZnO catalyst synthesis. We briefly introduce the fields of application of this catalyst: methanol synthesis, the water gas shift reaction, and methanol steam reforming. The review is focused on the well-documented industrial synthesis protocol and on the early stages of catalyst synthesis. The setting of the most critical synthesis parameters during co-precipitation and ageing, like pH and temperature, is discussed in detail. We show how these parameters effect the phase formation and identify zincian malachite, (Cu, Zn)2(OH)2CO3, as the relevant precursor phase for high-performance catalysts. A special emphasis is placed on the solid state chemistry of this precursor phase, in particular on the structural effects of Cu, Zn substitution. Based on the structural analysis, it is shown that the industrial synthesis recipe was empirically optimized to maximize the zinc incorporation into zincian malachite. From this insight a simple and generic geometric concept for the synthesis of nanostructured composite catalysts based on de-mixing of solid solution precursors is derived. With this concept, the complex multi-step industrial synthesis can be rationalized and the so-called “chemical memory” of this catalyst synthesis can be understood. We also demonstrate how application of this concept can lead to new interesting catalytic materials, which help to address fundamental questions of this catalyst system like to role of the Al2O3 promoter or the so-called Cu-Zn synergy.

A comparative study of Mn/CeO2, Mn/ZrO2 and Mn/Ce-ZrO2 for low temperature selective catalytic reduction of NO with NH3 in the presence of SO2 and H2O.

Abstract: Ce-ZrO2 is a widely used three-way catalyst support. Because of the large surface area and excellent redox quality, Ce-ZrO2 may have potential application in selective catalytic reduction (SCR) systems. In the present work, Ce-ZrO2 was introduced into a low-temperature SCR system and CeO2 and ZrO2 supports were also introduced to make a contrastive study. Mn/CeO2, Mn/ZrO2 and Mn/Ce-ZrO2 were prepared by impregnating these supports with Mn(NO3)2 solution, and have been characterized by N2-BET, XRD, TPR, TPD, XPS, FT-IR and TG. The activity and resistance to SO2 and H2O of the catalysts were investigated. Mn/Ce-ZrO2 and Mn/CeO2 were proved to have better low-temperature activities than Mn/ZrO2, and yielded 98.6% and 96.8% NO conversion at 180°C, respectively. This is mainly because Mn/Ce-ZrO2 and Mn/CeO2 had higher dispersion of manganese oxides, better redox properties and more weakly adsorbed oxygen species than Mn/ZrO2. In addition, Mn/Ce-ZrO2 showed a good resistance to SO2 and H2O and presented 87.1% NO conversion, even under SO2 and H2O treatment for 6 hours, and the activity of Mn/Ce-ZrO2 was almost restored to its original level after cutting off the injection of SO2 and H2O. This was due to the weak water absorption and weak sulfation process on the surface of the catalyst.