Fine Catalyst Research Articles

Intermetallic Compounds: Promising Inorganic Materials for Well-Structured and Electronically Modified Reaction Environments for Efficient Catalysis

An overview of the catalytic properties of intermetallic compounds has been made to provide a comprehensive understanding regarding (1) what intermetallic catalysts can do, (2) their fundamental roles in enhanced catalysis, and (3) their advantages over other inorganic materials. A number of chemical transformations using intermetallic catalysts have been surveyed and classified into three major divisions—hydrogenation/dehydrogenation, oxidation, and steam reforming and various subsections. The fundamental roles of intermetallic phases obtained from this survey were categorized into four types of effects: (a) electronic, (b) geometric, (c) steric, and (d) ordering effects. The unprecedented steric effects governed by the specific surface structures of intermetallic compounds highlight the unique capabilities of intermetallic materials. On the basis of this overview, we have concluded that intermetallic compounds have the following advantages for fine catalyst design: (i) control of the electronic structur...

Environment-Friendly Approach to Fabricate Iron Nanochains as a Superb Adsorbent and Recycled as a Fine Photo-Fenton Catalyst

Herein, a facile chemical reduction technique was used to fabricate iron nanochains under room temperature. They show high adsorption capacity of 480 mg g−1 and 100 mg L−1 of Orange ΙΙ can be almost removed within 1 min. More important thing is iron nanochains can be recycled as a photo-Fenton catalyst to continuously degrade Orange ΙΙ. Specifically, 98% of Orange ΙΙ could be decomposed within 100 min under simulated solar light irradiation and 80% of the degradation rate was maintained even after 6 successive cycles, indicating its good photocatalytic performance and reusability. Hence, iron nanochains reported in the paper realize the maximum reusability of materials. An environment-friendly approach to fabricate iron nanochains as a superb adsorbent and recycled as a fine photo-Fenton catalyst.

(Invited) Plasma Synthesis and Structural Control for Carbon Nanowalls for Novel Nano-Bio Devices

Carbon nanowalls (CNWs) are one of carbon nanomaterials. They consist of graphene sheets standing vertically on substrates, so that they have self-aligned three-dimensional structures. Significant recent attention has been focused on the functionalities of the CNWs because of their unique morphologies and excellent electrical properties. For example, since they have large surface-to-volume ratios and very high aspect ratios, they are expected as catalyst supporting materials in fuel cells, field emitters, and various kinds of templates. In addition, high-density graphene edges on the top-region of CNWs promise expression of novel functionalities and applications. In this study, we have investigated controlled synthesis techniques of carbon nanowalls, which have suitable morphologies and electrical properties for each device. Density ratios of hydrogen (H) and fluorocarbon (CFx (x=1-3)) radicals are essential to determine the density and height of CNWs, because the H radicals enhance desorption of fluorine (F) atoms from the adsorbed CFx. Ar+ ion irradiation is also important for the nucleation and vertical-growth of graphene sheets. According to observation results of their initial growth using ellipsometry and scanning electron microscopy, not only nucleation but also vertical-growth of graphene sheets could occur only under Ar+ ion irradiation with suitable energy and flux for each process. For example, when Ar+ion energy is too much, no film deposition occers due to etching. On the other hand, since too low energy ion bombardment can not induce nucleation of nanographen, only continuous amorphous carbon film grows on the substrate surface. Furthermore, when ion flux is too high, continuous amorphous carbon films grow too, since deposition rates of carbon related radicals much higher than growth rate of vertical graphene sheets. By using a supercritical fluid, high-density metal nanoparticles or metal oxide ones can be uniformly supported on the whole surface area of CNWs. For example, TiO2nanoparticles-supported CNWs efficiently desolve methylene blue molecules, which are typical test reagent for photocatalytic performance under UV irradiation. Pt nanoparticles-supported CNWs also show fine catalyst performance at cyclic voltammetry (CV) measurements. In addition, they also show very high durability at high potential cycle tests, which demonstrate start and stop operations of fuel cells. Furthermore, the CNWs also show multimodal and unique characteristic as cell culturing template. Preliminarily, the wide-range control of surface wettability of CNWs from superhydrophilic to superhydrophobic can be realized by the post-growth plasma treatments. Then, the dependence of the HeLa cell culturing rate and morphological change on the surface wettability of CNWs scaffolds was systematically evaluated. The cell culturing rates were significantly dependent on the CNW densities, although the surface wettability of the CNWs was not significantly dependent. Morphological changes of the cells were not significantly dependent on the density of CNWs. On the other hand, using the chemically surface-modified CNWs as electrodes, the CV characteristics were measured in PBS (PBS, pH 7) containing bovine serum albumin (BSA). Using the as-grown CNW electrode without Ar atmospheric pressure plasma treatment, weak oxidation and reduction peaks were observed in anode peak potential at 0.2 V and cathodic peak potential at -0.3 V, respectively. On the other hand, in the case of typical surface-oxidized CNW electrode, a broad oxidation peak was recorded with an anode peak potential of 0.2 V. A high peak reduction current was also observed in the cathodic peak potential at -0.75 V. In the case of surface-oxidized CNW electrode of low height, the CV profile exhibited small peak currents compared with the case using typical CNW-oxide electrode, due to the decrease of immobilized BSA on the reduced surface area. These results indicate that the high potentials of CNWs as a novel platform for nano-bio applications.

Precipitation in a Micromixer – From Laboratory to Industrial Scale

AbstractContinuous high‐intensity mixing of two fluids for carrying out fast precipitation is an important method for producing nanoparticulate solids for diverse applications, e.g., in fine chemistry, pigment or catalyst preparation. Continuous precipitation with a newly developed micromixer technology, the so‐called valve‐assisted micromixer, allows for stable operation without clogging for several days. Scale‐up to technically relevant scale was achieved without differences in the quality of the precipitate. The technology has been extensively tested for preparation of catalysts for production of carbon nanotubes.

Development of Tailored Porous Microstructures for Infiltrated Catalyst Electrodes by Aqueous Tape Casting Methods

Recent activities in SOFC research have shown the technique of impregnating fine catalyst structures into porous scaffolds to be an extremely promising route of development. Electrodes made in this way have shown promising performance with improvements in power density, carbon tolerance, redox tolerance and potentially sulphur tolerance. To gain the best cell performance it is likely that a supported electrolyte design will be favoured with the scaffold being fabricated by economically viable and scaleable techniques such as tape casting. It is clear that in optimising the advantages offered by the infiltration technique there will be an obvious link between the morphology of the porous scaffold and the infiltrated catalyst which is supported upon it. At present a significant amount of tape casting techniques are based around non-polar solvent systems. The solvents used in these systems, such as methyl ethyl ketone and toluene, can be quite aggressive and so limit the type of polymeric based pore former which can be employed to create porosity. There are also significant health and environmental issues with the use of such systems, such as flammability in exhaust systems at larger production scales and they are also coming under increasingly tight legislation with regards to handling, worker exposure and disposal. Minimising these make development of an aqueous system an attractive option. However the application of aqueous systems is not without issue. Attaining stable particle dispersions can be trickier due to the polar nature of the solvent leading to increased dipole interaction between slurry constituents and increased sensitivity to changes in pH. Furthermore the slurry can be more susceptible to local environmental changes such as temperature and humidity resulting in inconsistencies in tape quality. These factors have led to a slow uptake of aqueous systems in technical ceramic processing. However the potential benefits of aqueous systems for this application, such as a the potential for a far larger range of pore forming materials which may be employed to create specific pore morphologies, secondly the significantly reduced environmental burdens, such as exhaust handling, worker exposure and disposal, make their development for the production of porous scaffolds a valuable goal. Recent and ongoing activities to develop such systems at University of St Andrews will be described in this paper. A number of pore forming systems are under investigation, acrylic microspheres, rice starch, styrene-acrylic latex and sodium alginate, the latter is of additional interest due to its ability to cross-link allowing gel-casting techniques to be explored. Tapes have been manufactured using both YSZ and strontium and calcium doped lanthanum titanate (LSCT) as the ceramic phase with the pore formers used both individually and in combination with one another . The rheological behaviour of the wet tapes was assessed by rotational viscometry along with assessment of casting, drying and green properties. Tapes were fired in air over various times and temperatures with fired microstructures assessed by SEM examination and image analysis using “Image J” analytical software. Areas of discussion will be effects of ceramic particle type and size, the size ratio of pore former to ceramic particle, pore former type and loading and how these affect the interaction with other tape constituents both on the behaviour of the tape during processing and on the final fired morphology. How these relationships may be better understood and what implications they have in designing optimised porous structures in the future will also be discussed.

Development of Tailored Porous Microstructures for Infiltrated Catalyst Electrodes by Aqueous Tape Casting Methods

Recent SOFC research has shown that impregnating fine catalyst structures into porous scaffolds to be an extremely promising route for electrode development. It is clear that in optimising the advantages offered by this technique there will be an obvious link between the morphology of the porous scaffold and the infiltrated catalyst. There are significant potential benefits to using aqueous systems for the manufacture of the scaffold. They include the potential for a far larger range of pore formers which may be employed to create specific pore morphologies and also reduced environmental burdens, such as exhaust handling, worker exposure and disposal. Recent and ongoing activities to develop such systems at University of St Andrews will be described. Areas of discussion will be effects of ceramic particle size, the size ratio of pore former to ceramic particle, pore former type and loading and how these interact with other tape constituents both on the behaviour during processing and on the final fired morphology. Better understanding of these complex relationships will help in designing optimised porous structures in the future

Application of Minihydrocyclones in Methanol‐to‐Olefin Process Wastewater Treatment

AbstractA significant amount of wastewater containing fine catalyst particles is produced in the methanol‐to‐olefin (MTO) process, which restricts the long‐period operation of the processing unit. To address this key problem, a minihydrocyclone was designed for MTO wastewater treatment and tested in the laboratory. Good separation performance and a small cut diameter were achieved under certain feed conditions. Furthermore, a group composed of 300 parallel‐arranged minihydrocyclones was applied to the industrial unit in the MTO quench water treatment. The obtained results indicated that the separation efficiency and precision of the minihydrocyclone can meet the requirements of fine catalyst particle separation, and the designed minihydrocyclone group with reasonable parallel configuration exerted an outstanding application effect on the treatment of MTO quench water.

Treating Methanol‐to‐Olefin Quench Water by Minihydrocyclone Clarification and Steam Stripper Purification

AbstractIn the chemical industry, methanol‐to‐olefin (MTO) technology is a novel process for producing ethylene and propylene from naphtha thermal cracking. The process of recovering MTO quench water by minihydrocyclone and steam stripping treatment was successfully applied in industrial plants. The fine catalyst in the quench water is removed by the two‐stage minihydrocyclone separation. The method and equipment for this system present various advantages: the quench water can be recycled in the cooling system and prevents heat loss in heat transfer systems; and the stripping tower can be blocked by the catalyst. Maintenance activities are reduced and a stable operation cycle is extended. The proposed treatment process improves the economic efficiency of the MTO device.

무전해 동 도금을 위한 초음파 적용 주석-은-팔라듐 활성화 공정에 대한 연구

An ultrasound-assisted Sn-Ag-Pd activation method for electroless copper plating was presented in this study. With this activation process, it was shown that the fine catalyst particles were homogeneously distributed with high density on the entire specimen. In addition, it was observed that incubation period occurred during the electroless plating step was decreased owing to the absorption of Ag which holds high catalytic activity. Resulting from the refinement and high densification of catalyst, the defect-free gap-fill was achieved within the 20x nm trench.

The effect of encapsulated nanosized catalysts on the combustion of composite solid propellants

In solid rocket propellants, nano-sized catalysts are expected to be more effective than their micron-sized counterparts due to their higher surface area and increased contact with the oxidizer. However, propellant processing becomes more difficult and ultimate mechanical properties can be negatively impacted as catalyst size is reduced. One proposed solution to these issues is to encapsulate a nano-sized catalyst inside the oxidizer. We have previously created composite particles with nano-sized iron oxide catalyst encapsulated in fine ammonium perchlorate (AP). In this paper we explore the effect of the composite particles on the burning rate and flame structure of an AP-based composite propellant. The propellant containing the composite nano-iron oxide/AP particles was compared to a baseline propellant without catalyst, a propellant formulated with micron-sized catalyst, and a propellant with nano-sized catalyst mixed directly. All catalyzed propellants contained the same catalyst mass fraction. High-speed (5kHz) OH planar laser-induced fluorescence (PLIF) and high-speed surface imaging were used to examine differences in flame structure and coarse crystal burning characteristics and determine how the encapsulated catalyst influences the global burning rate. It was found that the burning rate of the propellant with the encapsulated catalyst was 90% higher than that of the baseline propellant, 44% higher than the propellant with micron-scale catalyst, and 15% higher than that of the propellant with nano-sized catalyst added directly. Our results indicate that the high global burning rate of the propellant with the encapsulated catalyst is due to an accelerating effect on the fine AP/binder matrix burning rate, assumed to be caused by the intimate contact between the fine AP and catalyst. At elevated pressures (4.4–7.1atm) flame structure and burning surface morphology change as the catalyst size and location is changed. The coarse crystals are observed to protrude more from the burning surface as the catalyst size decreases. The microscale flame structure is observed to transition from jet-like to lifted arches as the pressure and catalyst size increase.

Production of biodiesel fuel from canola oil with dimethyl carbonate using an active sodium methoxide catalyst prepared by crystallization.

In this study, a novel method for the production of biodiesel under mild conditions using fine particles of sodium methoxide formed in dimethyl carbonate (DMC) is proposed. Biodiesel is generally produced from vegetable oils by the transesterification of triglycerides with methanol. However, this reaction produces glycerol as a byproduct, and raw materials are not effectively utilized. Transesterification with DMC has recently been studied because glycerol is not formed in the process. Although solid-state sodium methoxide has been reported to be inactive for this reaction, the catalytic activity dramatically increased with the preparation of fine catalyst powders by crystallization. The transesterification of canola oil with DMC was studied using this catalyst for the preparation of biodiesel. A conversion greater than 96% was obtained at 65°C for 2h with a 3:1M ratio of DMC and oil and 2.0 wt% catalyst.

Soot oxidation in a corona plasma-catalytic reactor

Oxidation of soot by corona plasma was investigated at conditions of exhaust gases from diesel engines, both in the absence and presence of CoO x as a catalyst. The CoO x catalyst nanoparticles were synthesized by a precipitation method. The BET surface area of the catalyst was 50 m2/g, corresponding to 23 nm particles. An aluminum grid was sequentially dip-coated for several times by suspensions of the soot in toluene and/or fine catalyst powder in DI water. The grid was used as the plate of a pin-to-plate corona reactor. Air at 180 °C was passed through the corona reactor to oxidize the soot, oxidation products of which were analyzed by both gas chromatograph and FTIR with a gas cell. Soot oxidation rate linearly increased with an increase of input energy. When the soot was deposited on a layer of the CoO x catalyst, the soot oxidation rate increased up to 2 times. The only product of the plasma (catalytic) oxidation of soot was CO 2 determined by FTIR. O produced in the plasma discharge oxidized the soot and the active surface oxygen enhanced its rate.

Decrease in the fluidization quality of fluidized beds containing binary mixtures of different catalyst particles

Good fluidization was generally established when fine and light catalyst particles were fluidized. However, a large decrease in the fluidization quality was observed when two types of particles composed of different materials were mixed and fluidized, even though good fluidization was established with each type of particle alones. Formation of gas channeling was observed for binary mixtures of particles in a two-dimensional (2D) fluidized bed. In a three-dimensional (3D) bed, measurement of the pressure fluctuation showed that abnormal fluidization occurred due to mixing of the particles. In addition, measurements of the minimum fluidization velocity and emulsion phase expansion indicated that particle agglomeration occurred. The phenomena observed in the fluidized bed with the mixture of particles are quite similar to those observed for Group C particles. On the basis of the direction of the electrostatic charge, the particles were separated using electrodes installed above the fluidized bed surface. It was confirmed that one type of particle was positively charged and the other was negatively charged. Thus, it was concluded from these results that the bipolar charging caused by the difference in chemical composition of the particles induced the agglomeration phenomena and poor fluidization.

On the laboratory and field studies of removing fine particles suspended in wastewater using mini-hydrocyclone

Developments in different industries are leading to increased fine particles in industrial wastewater. Fine particle grading, separation, and recycling involve many problems, and the separation quality is directly related to the economic benefits and environmental effects. In this study, a mini-hydrocyclone with a nominal diameter of 25mm was designed and tested for the separation of fine catalyst particles from water in the laboratory. The method was also used in the industrial methanol-to-olefin (MTO) quench water treatment process. Under certain feed conditions in the laboratory experiment, the separation efficiency of the mini-hydrocyclone was around 88% and the particle cut size d50 was 1.70μm. The removal rate of particles larger than 3μm reached ⩾85%. The two stages of the mini-hydrocyclone separation process (i.e., clarification and concentrating) were examined, and the results showed that the process had high throughput and low loss. Recovery of MTO quench water by mini-hydroyclone and steam-stripping treatment were performed in an industrial plant. The cut size d50 in the industrial application was 1.68μm, which was close to that in the laboratory experiment. The stripping process removed ketone and methanol, which are poisonous and harmful components that prevent MTO quench water recovery. Furthermore, catalyst particles larger than 5μm were almost completely recycled. The recovery process of MTO quench water by mini-hydroyclone and steam-stripping treatment was successful. These results demonstrated that mini-hydrocyclone separation can be combined with other methods for the efficient treatment of industrial wastewater with fine particles.

Increased CNT growth density with an additional thin Ni layer on the Fe/Al catalyst film

Density of 3×1011/cm2 and diameter of CNTs of 9–12nm were successfully controlled by using the multi-layered catalyst film consisting of an additional Ni layer on Fe/Al catalyst film. EDS analysis for the annealed catalyst films revealed that the increase of the density of Fe catalyst particles corresponded with the decrease of Ni in the films, which strongly suggested that the additional thin Ni layer on the Fe/Al multi-layered catalyst films prevented the fine Fe catalyst particles from agglomeration, resulting in the growth of high-density, and uniform diameter of CNTs.

Solvent-free selective aerobic oxidation of toluene by ultra fine nano-palladium catalyst

High activity ultrafine Pd catalyst was synthesized by both functional polymer encapsulated and impregnation methods. Catalysts were characterized and used to catalyze solvent-free aerobic toluene oxidation. Reaction temperature, time, catalyst mass, air pressure and catalyst reusability were investigated. Catalyst synthesized by encapsulating and immobilizing Pd inside titanium oxide is more active and has a better reusability.

Characteristics of Pt, Pt-Ru and Pt-CeO_2 Catalysts Supported on Carbon Nanotubes for Methanol Fuel Cell

Nanosized Pt, Pt-Ru and Pt-<TEX>$CeO_2$</TEX> electrocatalysts supported on acid-treated carbon nanotube (CNT) were synthesized by microwave-assisted heating of polyol process using <TEX>$H_2Cl_6Pt{\cdot}6H_2O$</TEX>, <TEX>$RuCl_3$</TEX>, <TEX>$CeCl_3$</TEX> precursors, respectively, and were characterized by XRD and TEM. And then the electrochemical activity of methanol oxidation for catalyst/CNT nanocomposite electrodes was investigated. The microwave assisted polyol process produced the nano-sized crystalline catalysts particles on CNT. The size of Pt supported on CNT was 7~12 nm but it decreased to 3~5 nm in which 10wt% sodium acetate was added as a stabilizer during the polyol process. This fine Pt catalyst particles resulted in a higher current density for Pt/CNT electrode. It was also found that 10 nm size of PtRu alloys were formed by polyol process and the onset potential decreased with Ru addition. Cyclic voltammetry analysis revealed that the <TEX>$Pt_{75}Ru_{25}/CNT$</TEX> electrode had the highest electrochemical activity owing to a higher ratio of the forward to reverse anodic peak current. And the chronoamperemetry test showed that <TEX>$Pt_{75}Ru_{25}$</TEX> catalyst had a good catalyst stability. The activity of Pt was also found to be improved with the addition of <TEX>$CeO_2$</TEX>.

Magnetic field enhances the graphitized structure and field emission effect of carbon nanotubes

This study uses a low temperature thermal chemical vapor deposition with an applied external magnetic field to grow carbon nanotubes (CNTs) on Ni/Ag-printed glass substrates. A mixture of C 2H 2 and H 2 gas was used for the growth of the CNTs. A Ni catalyst layer was deposited on the Ag-printed glass substrate by pulse electroplating. Scanning electron micrographs as well as the presence of two sharp peaks at 1320 cm −1 (D band) and 1590 cm −1 (G band) in the Raman spectra indicate that the graphitized structure of CNTs synthesized under a magnetic field has higher quality (i.e., a D-band to G-band intensity ratio of 0.303) than CNTs synthesized without a magnetic field. Transmission electron micrographs show a fine Ni catalyst at the tip of the tube for CNTs synthesized under a magnetic field, exhibiting a CNT “tip-growth” model. The synthesis of CNTs in the presence of a magnetic field also generates better field emission properties and better lighting morphology than without a magnetic field.

Liquid/Liquid Slug Flow Capillary Microreactor

AbstractThe liquid‐liquid slug flow capillary microreactor offers an excellent mass transfer performance for extraction and biphasic reactions. In combination with a simple phase separator based on wettability discrimination between the two liquids, it provides a powerful tool for process intensification and microscale processing. By new visualization techniques, the interfacial surface and slug vortex structures dictating inter‐ and intraphase mass transfer have been revealed to be more complex than previously assumed. Suspending fine catalyst particles in one phase of a two‐phase slug flow is an effective technique for using heterogeneous catalysts in microreactors, owing to the very good mass transfer characteristics and because catalyst recovery becomes simply a matter of separating the catalyst carrier phase from the reaction medium. To exploit the performance attributes of capillary microreactors at higher throughputs, distributor and control strategies for parallelisation were developed to provide a flow distribution uniform to within 1 % or less.

Precious Metal Reduction by Improving Promoter Function in Ultra Fine Precious Metal Catalyst

Precious Metal Reduction by Improving Promoter Function in Ultra Fine Precious Metal Catalyst