Catalyst Metal Loading Research Articles

Study of the Preparation and Property of Oxygen Reduction Electrode Based on Polyaniline or Polypyrrole

Polyaniline (PANI) and polypyrrole (PPy) is developed rapidly with special physical and chemical performance. According to high catalytic activity, polyaniline is applied in a wide range of electrocatalysis area, especially for oxygen reduction. In this paper, electrochemical prepared polyaniline was used as catalyst as well as the loading of noble metal catalyst for manufacturing oxygen reduction electrode. Then the influence of carrier, noble metal and their binding forms to the ability of oxygen reduction were investigated by cyclic voltammeter. The result shows that PANI carrier was the most influential factor for oxygen reduction; for single noble metal catalyst, Pt shows bigger catalytic activity than Ag. And the best catalytic activity was optimized at dual deposited catalyst as Ag, Pt mass ratio to 23:100. Further more; compared to glassy carbon, graphite is much better for electrode basement.

Supporting PtRu catalysts on various types of carbon nanomaterials for fuel cell applications

PtRu catalysts were supported on five types of carbon nanomaterials of various shapes, sizes, and graphitic properties and the catalyst supports evaluated. The carbon nanomaterial used included three types of nanoparticles: Arc Black (AcB), Vulcan XC-72 (Vulcan) and graphene oxide (GO), and two types of nanofibers: carbon nanocoil (CNC) and carbon nanotube (CNT). Pt and Ru were supported by the reduction method using sodium borohydride. The metal catalyst loading was confirmed by thermo-gravimetric analysis (TGA), electron microscopy, and X-ray diffraction (XRD). Transmission electron microscopy (TEM) and XRD revealed that the diameter of PtRu catalyst nanoparticles loaded on reduced GO (rGO) and AcB were ~2 nm and was the smallest among all the samples. Shifts in Pt (111) XRD peaks of CNC and CNT were larger than those of AcB, Vulcan, and rGO. These results suggest that the diameters of catalyst nanoparticles became smaller by loading on the carbon nanoparticles with a large surface area including rGO, AcB, and Vulcan. Loading onto the carbon nanofibers enhanced the degree of PtRu alloying.

Hydrogen production from solar driven glucose oxidation over Ni(OH)2 functionalized electroreduced-TiO2 nanowire arrays

Herein, we demonstrated that solar driven glucose oxidation to produce hydrogen has been achieved on a functionalized TiO2 nanowire arrays photoanode without expensive metal catalyst loading. The Ni(OH)2 functionalized the electro-reduced TiO2 NWAs photoanode exhibits a much lower onset potential, substantially higher oxidation current density and good stability for glucose oxidation.

A direct glucose alkaline fuel cell using MnO2–carbon nanocomposite supported gold catalyst for anode glucose oxidation

Gold nanoparticles supported on MnO2–carbon nanocomposite (Au/MnO2–C) are synthesised as the catalyst for the anodic oxidation of glucose for use in a direct glucose alkaline fuel cell (DGAFC). Characterisation of the catalyst is carried out using physical and electrochemical methods. It is observed that gold nanoparticles are uniformly dispersed onto the MnO2–carbon nanocomposite support. Cyclic voltammetry shows that the prepared Au/MnO2–carbon catalysts exhibit higher electro–catalytic activity for glucose oxidation than that of commercial Pt/C and Au/C catalysts. A maximum power density, at 30 °C, of 1.1 mW cm−2 is obtained using an Au/MnO2–C anode catalyst in DGAFC, which is higher than that of the commercial Au/C catalyst. The enhanced activity is attributed to a catalytic effect of MnO2 towards glucose oxidation. MnO2–C nanocomposite is a promising approach for reducing noble metal catalyst loading in addition to improving the catalytic activity of gold catalyst for glucose oxidation.

Hydroprocessing of heavy gas oils using FeW/SBA-15 catalysts: Experimentals, optimization of metals loading, and kinetics study

In the present work, a series of FeW/SBA-15 catalysts were prepared and screened for their hydrodesulfurization and hydrodenitrogenation activities using bitumen-derived heavy gas oil from Athabasca. A systematic process optimization study has been conducted to investigate the optimum process conditions required to evaluate kinetic parameters for these reactions. Catalyst metal loadings were varied from 0 to 5 and 15 to 45wt.% for Fe and W, respectively; resulting in an optimum catalyst (Cat-5) with metal loadings of 3.0 and 30.0wt.% for Fe and W, respectively. Several techniques were employed to characterize the prepared catalysts and activity results have been correlated with that obtained from characterization. Hydrotreating experiments were performed in a continuous flow micro trickle-bed reactor at the temperatures, pressures, and LHSVs of 633–693°K, 7.6–9.6MPa, and 0.5–2h−1, respectively, with H2 flow rate and catalyst weight maintained constant at 50mL/min and 1.5g, respectively, in all cases. Three kinetic models were applied to fit experimental data obtained from HDS and HDN reaction studies evaluated within temperature range of 633–693°K. The optimum operating conditions for maximum sulfur and nitrogen conversions occurred at temperature, pressure, and LHSV of 673°K, 8.8MPa, and 1h−1, respectively. Experimental data fitted with the Power Law model yielded reaction orders of 2.0 and 1.5 for HDS and HDN reactions, respectively; and activation energies of 129.6kJ/mol and 150.6kJ/mol, respectively. By fitting a modified power law model (Multi-parameter model) to the kinetic data yielded hydrodesulfurization (HDS) and hydrotreating (HDN) reactions orders of 2.2 and 1.8, with respective activation energies of 126.7kJ/mol and 118.8kJ/mol.

Cathode Materials for Polymer Electrolyte Fuel Cells Based on Vertically Aligned Carbon Filaments

Polymer electrolyte fuel cells (PEMFC) suffer dramatic loss of an operating voltage due to a significant cathode overpotential calling for economically unviable noble metal catalyst loadings in the cathode active layers. Therefore significant effort is put into the investigation of the cathode oxygen reduction reaction (ORR) and the development of novel electrocatalytic materials. In this presentation we discuss catalytic materials based on platinum nanoparticles supported on vertically aligned carbon nanofilaments. They are intended to improve mass transport, Pt utilization and corrosion stability of the cathode. They are also of interest as a model system for shedding light on the kinetics and mechanisms of fuel cell reactions.

Optimization of Carbon Nanotubes Synthesis via Methane Decomposition over Alumina-Based Catalyst

Carbon nanotubes (CNTs) were synthesized from alumina-based catalyst via decomposition of methane in a horizontal reactor system. By using statistical design of experiments (DoE), six process variables (reaction temperature, reaction duration, metal loading of catalyst, amount of catalyst, flow rate of methane and flow rate of nitrogen) were optimized for the synthesis of CNTs with satisfying quality. The response of the process towards the process variables was assessed using two quantitative signifiers, which are the yield of carbonaceous material and the ID/IG ratio from Raman spectrum. A total of 23 runs was required to achieve the optimum condition: 9 runs for the screening of decisive process variables by using Resolution III fractional factorial design (FFD), 13 runs for the response surface incurred from Box-Behnken design and 1 run for the validation of the final optimum condition. The optimum parameter set was found at a reaction temperature, reaction duration and metal loading of 762°C, 2.3h and 27%, respectively with the carbon yield and ID/IG of 350.0% and 0.595, respectively.

One‐Pot Synthesis of Lactide–Styrene Diblock Copolymers via Catalytic Immortal Ring‐Opening Polymerization of Lactide and Nitroxide‐Mediated Polymerization of Styrene

An efficient, practical, and industrially relevant procedure for the production of polymer materials, in which a part of the oil-derived polyolefins has been replaced by a renewable, biodegradable, and biocompatible poly(lactide) block, is presented. Binary catalytic systems combining innocuous metals (yttrium, zinc, magnesium, or calcium) and bifunctional alcohols (acting as transfer agents) were developed to promote the immortal ring-opening polymerization of lactide directly in styrene. Up to 20,000 equivalents of lactide were polymerized (metal catalyst loading of 50-100 ppm) in a controlled fashion in the presence of 10-100 equivalents of a double-headed transfer agent to give as many end-functionalized poly(lactide) macromolecules that can be used eventually as macroinitiators for the controlled nitroxide-mediated polymerization of styrene. The specific use of the sterically shielded complex [BDI-iPr]Zn-N(SiMe(3))(2) ([BDI-iPr]=bis(diketiminate) ligand) allowed the efficient, catalytic, and controlled production of poly(lactide)-block-poly(styrene) materials in a one-pot, solvent-free sequential procedure, with nearly 100% atom-efficiency.

Hydrogenation of 2-Butyne-1,4-diol Using Novel Bio-Palladium Catalysts

Palladium catalyst samples were prepared upon bacterial biomass supports (Gram-positive A. oxidans and Gram-negative R. capsulatus) and tested in the partial hydrogenation of 2-butyne-1,4-diol to 2-butene-1,4-diol. The objectives of the study were to assess the effects of operating conditions in the stirred autoclave upon the reaction conversion and selectivity and to compare the biologically supported palladium (BioPd) catalyst performance with that of a conventionally supported catalyst. Variables investigated included solvent, stirring speed, and catalyst metal loading. A maximum selectivity toward 2-butene-1,4-diol of 0.98 was observed in a solvent composed of 5% isopropyl alcohol (2-propanol) in water at a conversion of 75% 2-butyne-1,4-diol for the Pd/A. oxidans catalyst. The Pd/R.capsulatas catalyst showed a maximum selectivity of 1.0 at a conversion of 62.6%. Concentration profiles of the different hydrogenation products were fitted using a Langmuir−Hinshelwood expression, which showed a higher fitted adsorption constant of 2-butyne-1,4-diol in a 5% 2-propanol/water solvent, compared with pure 2-propanol, suggesting that adsorption is stronger in the mixed solvent. At a typical catalyst loading of 0.29 g/L (Pd/R. capsulatus), analysis of the mass-transfer steps in the reactor showed that ∼63% of the resistance to mass transfer lies at the catalyst (liquid−solid) particle and ∼37% lies at the gas bubble interface. BioPd was proven to be a highly selective catalyst for partial hydrogenation reactions and has the advantage that it can be prepared inexpensively from metal-waste-bearing solutions.

Self-assembled mesoporous carbon films for platinum metal catalyst loading

This work demonstrates the use of self-assembled carbon films in designing fuel cell electrode. Well-dispersed mesoporous carbon particles were prepared based on the spontaneous and strong chemisorption of polyoxometalate (POM) solution on carbon surface. Electrostatically self-assembled films of the POM stabilized carbon interlaced with cationic polyelectrolyte binding layer were useful for confining electrodeposition of platinum (Pt) catalyst. The structure and morphology of the resulting films were characterized by X-ray diffraction and scanning electron microscopy respectively. The electrocatalytic activities of Pt deposited on the self-assembled carbon films toward the degradation of small organic molecules are largely dependent on the quantity of Pt and carbon. This work represents a simply controlled test-bed for fundamental studies on loading metal catalysts on ordered mesoporous carbon films for catalysis.

Poly(trimethylene carbonate) from Biometals‐Based Initiators/Catalysts: Highly Efficient Immortal Ring‐Opening Polymerization Processes

Abstractmagnified imageThe ring‐opening polymerization (ROP) of trimethylene carbonate (TMC) was evaluated in bulk at 60–110 °C using various catalyst systems based on bio‐friendly metals, including the metal bis(trimethylsilylamides) Mg[N(SiMe3)2]2, Ca[N(SiMe3)2]2(THF)2, Y[N(SiMe3)2]3, (BDI)Fe[N(SiMe3)2] [BDI=CH(CMeNC6H3‐2,6‐i‐Pr2)2], Fe[N(SiMe3)2]2, Fe[N(SiMe3)2]3, Zn[N(SiMe3)2]2, (BDI)Zn[N(SiMe3)2] and ZnEt2, associated with an alcohol such as isopropyl or benzyl alcohol. The actual metal alkoxide initiating species has been formed in situ prior to the addition of TMC. Introduction of the alcohol component in excess leads to the “immortal” ring‐opening polymerization (ROP) of TMC. According to such an “immortal” ROP process of TMC, whichever the metal species, as many as 200 polycarbonate chains could be successfully grown from a unique metal center in a well controlled ROP process. The best performances were obtained using the discrete (BDI)Zn[N(SiMe3)2] precursor. Under optimized conditions, as many as 50,000 equivalents of TMC could be fully converted from as little as 20 ppm of this metallic precursor, allowing the preparation of a polytrimethylene carbonate (PTMC) with a molar mass as high as 185,200 g mol−1 with a relatively narrow molar mass distribution (Mw/Mn=1.68). A double monomer feed experiment carried out with the (BDI)Zn[N(SiMe3)2]/BnOH initiating system proved the “living” character of the polymerization. Characterization of the PTMCs by NMR and size exclusion chromatography (SEC) showed well‐defined α‐hydroxy‐ω‐alkoxycarbonate telechelic polymers, highlighting the controlled character of this “living and immortal” ROP process. Using the (BDI)Zn[N(SiMe3)2] precursor, varying the alcohol (ROH) to 2‐butanol, 3‐buten‐2‐ol or 4‐(trifluoromethyl)benzyl alcohol, revealed the versatility of this approach, allowing the preparation of accordingly end‐functionalized HO‐PTMC‐OR polymers. The very low initial loading of metal catalyst considerably limits the potential toxicity and thus allows such polycarbonates to be used in the biomedical field.

DMFC electrode preparation, performance and proton conductivity measurements

A method that involves stenciling electrodes using dry powders for fuel cells is described and compared to anodes and cathodes prepared by the traditional spraying method using catalyst inks. Methods to determine the proton conductivity of the DMFC anode layer are also discussed. The stenciling method allows for the preparation of highly reproducible membrane electrode assemblies (MEAs) utilizing little waste material. MEAs can be prepared in a controlled manner using the stenciling technique. The resulting morphology of the as-prepared electrodes is observed to be dependent on the preparation method, while the thickness of the once hot-pressed catalyst layers appears to be independent of the preparation method. Stenciled anodes of the same catalyst loading were found to show a lower proton resistance (Rp) than sprayed anodes. However, the lower Rp value was not sufficient to result in a measurable increase in the performance of a direct methanol fuel cell (DMFC); as in fact, the average steady-state DMFC performance was found to be the same using sprayed or stenciled electrodes. The DMFC performance was found to be strongly dependent on the Nafion content and large increases in the Nafion content were needed to increase the DMFC performance measurably. Even though thick electrodes were prepared in this work, the Rp values of the stenciled anodes were found to be comparable to results reported in the literature for much thinner electrodes made using high metal catalyst loadings on carbon. This observation is most probably due to the higher Nafion content used in this work.

CaCo3 supported Co‐Fe catalysts for carbon nanotube synthesis in fluidized bed reactors

AbstractThe synthesis of carbon nanotubes (CNTs) on a cobalt‐iron (Co‐Fe) catalyst supported on a calcium carbonate (CaCO3) substrate, contained within a fluidized bed was investigated for the first time. CaCO3 supported catalysts, prepared using traditional wet impregnation techniques result in a soft and sticky powder requiring special arrangements to ensure satisfactory fluidization. A modified method developed using citric acid complex resulted in CaCO3 supported catalysts that can be classically fluidized without special arrangements. The issue of Fe3+ (aq) hydrolysis above its critical pH of ∼3.5 was also addressed. A carbon yield consistently greater than 10 times the weight of the catalyst metal loading was obtained. Thermogravimetric analysis coupled with mass spectrometry showed a single peak centered on 575°C, with no peaks below 400°C, indicating that an insignificant quantity of amorphous carbon was present. Transmission electron microscopy verified that the products contained a large proportion of CNTs. © 2008 American Institute of Chemical Engineers AIChE J 2008

An internal reformer for a pressurised SOFC system

A novel reformer design has been demonstrated that converts the methane required for a multi kilowatt SOFC stack. Results show the influence of temperature and the benefits of operating at elevated pressure on the reforming-catalyst fundamental reaction kinetics. Due to the high heat demand of the steam reforming reaction, efficient heat transfer between the SOFC stack and the reforming catalyst is essential. Parameters such as the volume/surface area ratio, choice of catalyst, and catalyst metal loading are key to the design, and these have been determined through a combination of computer modelling and experimental measurements. The thermal properties of the unit have been evaluated over a range of temperatures and fuel compositions that simulate system operating-conditions in the final product.

Activity and Selectivity of Novel Structured Pd-Catalysts: Kinetics Modeling of Vegetable Oils Hydrogenation

Hydrogenation of sunflower oil over novel structured catalysts with pore size ranging from 3 to 20 nm, BET-specific surface area of 710-1200 m²/g, and catalyst metal loadings ranging from 0.7 to 5.0 % w/w, was investigated and compared to a commercial Ni-catalyst. The activity and selectivity of the catalysts as well as profiles of the reaction products such as trans fatty acids (TFA) of the hydrogenated oils were investigated. Surface characteristics of the support and the metal loading significantly affected the activity and selectivity of the Pd-catalysts. Catalyst supports with the pore diameter between 7-8 nm were more active than supports with lower pore diameters. The activity and selectivity of hydrogenation depended on Pd content, with maxima in the concentration range of 0.8 to 1.2 % w/w.The catalyst with Pd-loading of 1% w/w, supported on structured silica material was active and selective for the hydrogenation of sunflower and canola oils under mild process conditions. For same iodine value (IV) reduction, this catalyst produced about the same level of TFA, but produced less stearic acid and was more selective towards cis monoenes formation than Ni-catalyst. More importantly, this catalyst produced a reduced level of stearic acid which causes waxy mouth feel of the hydrogenated fat at increased levels.The lumped kinetic model of the hydrogenation of vegetable oils over Pd as well as Ni catalysts was found useful in the prediction of the fate of reaction and product lumps and was statistically robust. The uncertainty and confidence joint regions were estimated using the Bootstrap “Monte Carlo” technique.

Catalytic engineering of carbon nanotube production

The impact of some engineering aspects such as space velocity, catalyst metal loading, hydrogen, and temperature on carbon nanotube (CNT) production rate, productivity, and morphology in carbon monoxide disproportionation has been studied. The morphology and quality of the CNTs produced were examined by high resolution transmission electron microscopy (TEM). It was found that space velocity and metal loading have significant effects on the production rate and CNT productivity. The presence of H 2 dramatically increased the productivity, but altered the CNT structure. The synthesis temperature also influenced the carbon productivity and structure. The results were interpreted according to the traditional model for CNT growth, and the implications for large-scale CNT production were suggested.

( S)-1-Aminoindane: synthesis by chirality transfer using ( R)-phenylglycine amide as chiral auxiliary

A practical asymmetric synthesis of nearly enantiomerically pure ( S)-1-aminoindane has been developed. The key step involves the diastereoselective heterogeneous metal-catalyzed reduction of the ketimine of 1-indanone with the chiral auxiliary ( R)-phenylglycine amide. The selectivity of the asymmetric hydrogenation step was optimized with regard to metal catalyst, solvent and catalyst loading. The chiral auxiliary was removed by means of a novel non-reductive procedure. Thus, ( S)-1-aminoindane with an ee of 96% was prepared in 58% overall yield from ( R)-phenylglycine amide in an effective three-step procedure.

Novel microfabrication approaches for directly patterning PEM fuel cell membranes

We have successfully developed miniature hydrogen-air proton exchange membrane (PEM) fuel cells (FC) on silicon and poly-dimethylsiloxane (PDMS) base substrates using conventional and non-conventional microfabrication technologies. Prototype base substrates were fabricated by using well-known micromachining technologies, such as photolithography, deep reactive ion etching, and soft lithography. Sputtering, a physical vapor deposition method, was used to deposit catalysts and electrodes directly on the surface of the Nafion PEM. This paper describes the novel microfabrication approaches employed to selectively deposit electrodes and catalyst materials on the membrane with improved morphology and structure of electrodes. The aim was to reduce precious metal catalyst loadings, ohmic (iR) losses, and to improve structural support for the thin-film FC with concurrent reduction in fabrication complexity.

Kinetics of CH4Decomposition on Supported Cobalt Catalysts

A model of the kinetics of CH4decomposition on supported Co catalysts, at conditions relevant to the two-step CH4homologation reaction (450°C, 101 kPa), is presented. The model includes the decomposition of gas phase CH4on a Co site and migration of the resulting CHxfragment from the Co to the support as the key kinetic steps in the decomposition reaction. The migration step is essential to explain the observed kinetics at long reaction times (2–7 min) or high CH4feed concentrations (5% CH4in Ar). At these conditions, CH4decomposition continues at a low but constant rate despite a nominal Co coverage by CHx>1. The magnitudes of the estimated rate constants for the decomposition and migration steps are used to interpret the observed effects of temperature, catalyst metal loading, support, and K promoter on the CH4decomposition kinetics.

Low Cost Electrodes for Proton Exchange Membrane Fuel Cells: Performance in Single Cells and Ballard Stacks

For widespread exploitation of proton exchange membrane fuel cells (PEMFCs) the cost of the stack must be reduced, and the performance per unit volume increased. Significant cost reduction has been achieved by the development of a high‐volume, low cost, electrode manufacturing process and from reductions in the electrode precious metal catalyst loadings. The performance of membrane electrode assemblies (MEAs) employing printed cathodes (⩽0.6 mg Pt/cm2) and anodes (⩽0.25 mg Pt/cm2, 0.12 mg Ru/cm2) in Ballard Mark V single‐cell and advanced‐stack hardware are at least comparable to current stack MEAs comprising high loading unsupported platinum black electrodes containing 4.0 mg Pt/cm2. Optimum cell performance has provided high power densities of 0.42 W/cm2 at 0.7 V. Furthermore, under motive and utility test conditions, the low‐cost electrodes show minimal loss in performance after over 3000 h of stack operation and, in short and full sized stacks, the cell‐to‐cell reproducibility is excellent, highlighting the high consistency of product available from the electrode manufacturing process. Incorporation of the low cost electrodes in commercial PEMFC stacks is anticipated in the near future.