Low Metal Loading Research Articles

Ionic liquid-assisted synthesis of Pt nano thin films at toluene–water interface: Enhanced CO tolerance in methanol fuel cells and adsorptive removal of p-nitrophenol from water

In this investigation, we report a one-pot method for the synthesis of Pt/ionic liquid nano thin films at organic-aqueous media at room temperature without using any harsh conditions. Synthesized Pt/ionic liquid thin films were characterized with common analytical techniques. Transmission electron microscope images confirmed the formation of spherical particles having a size distribution in the range of 4–12 nm. Ionic liquids have a key role in the control of better size distribution and prevent from agglomeration of nanostructures by preparing a shell around particles. These catalysts were applied for the reduction of toxic p-nitrophenol into non-toxic p-aminophenol and exhibited good catalytic activity. Also, they exhibit excellent CO tolerance in methanol oxidation process of fuel cells. This method provides a novel, rapid, low cost and economical alternative for the reduction of toxic organic pollutants in water and also to prepare high quality catalysts with low metal loading for methanol fuel cells. Pt/1-aminoethyl-3-methylimidazolium bromide exhibits better CO tolerance than Pt/1-methyl-3-octylimidazolium chloride and Pt/1-methyl-3-octylimidazolium tetrafluoroborate thin films.

Gas-phase electrocatalytic conversion of CO2 to chemicals on sputtered Cu and Cu–C catalysts electrodes

Abstract A novel gas-phase electrocatalytic cell containing a low-temperature proton exchange membrane (PEM) was developed to electrochemically convert CO2 into organic compounds. Two different Cu-based cathode catalysts (Cu and Cu–C) were prepared by physical vapor deposition method (sputtering) and subsequently employed for the gas-phase electroreduction of CO2 at different temperatures (70–90 °C). The prepared electrodes Cu and Cu–C were characterized by X-ray diffraction (XRD), X-ray photoemission spectroscopy (XPS) and scanning electron microscopy (SEM). As revealed, Cu is partially oxidized on the surface of the samples and the Cu and Cu–C cathodic catalysts were comprised of a porous, continuous, and homogeneous film with nanocrystalline Cu with a grain size of 16 and 8 nm, respectively. The influence of the applied current and temperature on the electro-catalytic activity and selectivity of these materials was investigated. Among the two investigated electrodes, the pure Cu catalyst film showed the highest CO2 specific electrocatalytic reduction rates and higher selectivity to methanol formation compared to the Cu–C electrode, which was attributed to the higher particle size of the former and lower CuO/Cu ratio. The obtained results show potential interest for the possible use of electrical renewable energy for the transformation of CO2 into valuable products using low metal loading Cu based electrodes (0.5 mg Cu cm−2) prepared by sputtering.

An Efficient Protocol for the Synthesis of Primary Amides via Rh‐Catalyzed Rearrangement of Aldoximes

AbstractA system consisting of catalytic amounts of [Rh(CH2=CH2)Cl]2/PPh2Cy, and PhCl as the solvent efficiently catalyzes selective rearrangement of aldoximes to furnish various primary amides in moderate to good yields. Replacing the [Rh(CH2=CH2)Cl]2 with Rh(NBD)2OTf enables the superior transformation to afford the amides with up to 99% yields. Attractive synthetic features associated with this methodology include absence of co‐catalysts, broad functional group tolerance, good to excellent yields, low metal loadings, and operational convenience.

Synergistic role of Brønsted and Lewis acidity in alkali metal-exchanged heteropolyacid catalysts for esterification of acetic acid at room temperature

A series of Cs exchanged phosphotungstic acid (PTA) catalysts were synthesized by the ion exchanged method and were characterized by X-ray diffraction, FT-IR spectroscopy, pyridine adsorbed FT-IR spectroscopy, SEM, BF-TEM, ICP-OES and BET surface area analysis. For comparison purposes, K exchanged PTA, Cs and K exchanged phosphomolybdic acid (PMA) catalysts were also prepared. XRD diffractograms showed that the crystallites of the Keggin ion are maintained, while FT-IR spectra also revealed the characteristic bands of the Keggin ion at all metal loadings of all the catalysts. From pyridine adsorbed FT-IR spectroscopy, it was observed that the Bronsted and Lewis acidity were significantly maintained at lower metal loadings, whereas STEM analysis showed a uniform distribution of the elements which correlated well with the theoretical atomic values of the loaded metals for all the catalysts, which were verified by ICP results. The efficiency of various metal-exchanged heteropolyacid catalysts was assessed for the esterification reaction using various substrates, and the Cs exchanged phosphotungstic acid catalysts showed superior activity compared to the other catalysts. In particular, the Cs exchanged phosphotungstic acid with a 1 wt% loading showed the highest activity and was most tolerant to the presence of water that was produced in the reaction. The catalytic activity correlates well with the Bronsted and Lewis acidity, as well as Keggin ion density of the catalysts.

Selective Oxidation of Methane to Methanol Using Supported AuPd Catalysts Prepared by Stabilizer-Free Sol-Immobilization

The selective oxidation of methane to methanol, using H2O2, under mild reaction conditions was studied using bimetallic 1 wt % AuPd/TiO2 prepared by stabilizer-free sol-immobilization. The as-prepared catalysts exhibited low, unselective oxidation activity and deleterious H2O2 decomposition, which was ascribed to the small mean particle size of the supported AuPd nanoparticles. Heat treatments were employed to facilitate particle size growth, yielding an improvement in the catalyst turnover frequency and decreasing the H2O2 decomposition rate. The effect of support phase was studied by preparing a range of AuPd catalysts supported on rutile TiO2. The low surface area rutile TiO2 yielded catalysts with effective oxygenate production but poor H2O2 utilization. The influence of the rutile-TiO2 support was investigated further by producing catalysts with a lower metal loading to maintain a consistent metal loading per square meter compared to the 1 wt % AuPd/P25 TiO2 catalyst. When calcined at 800 °C, the 0.1...

Atomically Dispersed Transition Metals on Carbon Nanotubes with Ultrahigh Loading for Selective Electrochemical Carbon Dioxide Reduction

Single-atom catalysts (SACs) are the smallest entities for catalytic reactions with projected high atomic efficiency, superior activity, and selectivity; however, practical applications of SACs suffer from a very low metal loading of 1-2 wt%. Here, a class of SACs based on atomically dispersed transition metals on nitrogen-doped carbon nanotubes (MSA-N-CNTs, where M = Ni, Co, NiCo, CoFe, and NiPt) is synthesized with an extraordinarily high metal loading, e.g., 20 wt% in the case of NiSA-N-CNTs, using a new multistep pyrolysis process. Among these materials, NiSA-N-CNTs show an excellent selectivity and activity for the electrochemical reduction of CO2 to CO, achieving a turnover frequency (TOF) of 11.7 s-1 at -0.55 V (vs reversible hydrogen electrode (RHE)), two orders of magnitude higher than Ni nanoparticles supported on CNTs.

Porous carbon electrocatalyst with exclusive metal-coordinate active sites for acidic oxygen reduction reaction

A porous P-doped M/N/C electrocatalyst with high-surface-area (up to 1312 m2 g−1) was prepared by annealing a mixture of triphenylphosphine, polyaniline, phthalocyanine iron (II), and phthalocyanine cobalt (II). The synthesis involves hard templating with silica nanoparticles, followed by NH3 activation. Along with low metal loading (Fe loading = 0.46 wt. %; Co loading = 0.26 wt. %), the resulting P-doped M/N/C exhibits an excellent ORR activity and durability in acidic media. The half-wave potential difference of the catalyst for ORR is only ∼53 mV negative relative to the benchmarked Pt/C (360 μg Pt) at the same loading. More importantly, transmission electron microscopy, X-ray absorption fine structure spectra, and electrochemical poisoning by SCN− ion suggested that exclusive metal-coordinate catalytic active sites such as Fe-N6 and Co-N4, are involved in ORR. Moreover, as-prepared P-doped M/N/C catalysts with bimetallic catalytic active sites exhibit superior electrochemical performance compared to catalysts with single metal active sites. These results represent an important step towards rational design of high-performance ORR electrocatalysts for polymer exchange membrane fuel cells.

Maintenance of photosynthesis by Betula populifolia in metal contaminated soils

Improving our understanding of plant responses to elevated trace metal concentrations under field conditions will enhance restoration and urban greening practices in settings with contaminated soils. This study examined the effects of trace metal pollution on the leaf gas exchange rates of mature, field-grown Betula populifolia Marsh. (gray birch) trees, additionally assessing whether elevated temperature and drought compounded the effects of trace metal contamination. The study compared B. populifolia growing in areas of comparatively high and low trace metal loads (HML and LML, respectively) within a former rail yard at Liberty State Park in Jersey City, New Jersey, USA. Gas exchange parameters were determined monthly from May through September in 2014 and 2015 using a portable photosynthesis system. The effects of drought and high temperature were assessed during a short heat wave in July 2015 and via a manipulative experiment, respectively. During a few of the measurement months, some parameters differed significantly between the LML and HML groups. However, when considered over the entire study period, no significant differences in biophysical parameters were observed between groups. The photosynthetic capacity of B. populifolia thus appears to be fairly robust across this site's steep gradient of trace metal contamination. Nonetheless, leaf mass per unit area was significantly lower in the HML group, indicating that metal loads affected resource allocation within trees. Also, immediately following the heat wave in 2015, intrinsic water use efficiency declined significantly in the HML group, suggesting that extreme climatic conditions can have a disproportionate effect on the physiological performance of plants growing in metal contaminated soils.

Analysis of Voltage Losses in PEM Water Electrolyzers with Low Platinum Group Metal Loadings

In this study, the influence of catalyst loading on the performance of a proton exchange membrane (PEM) water electrolyzer is investigated (Nafion 212 membrane; IrO2/TiO2 (anode) and Pt/C (cathode)). Due to the fast kinetics of the hydrogen evolution reaction (HER) on platinum (Pt), the Pt loading on the cathode can be reduced from 0.30 mgPt cm−2 to 0.025 mgPt cm−2 without any negative effect on performance. On the anode, the iridium (Ir) loading was varied between 0.20–5.41 mgIr cm−2 and an optimum in performance at operational current densities (≥1 A cm−2) was found for 1–2 mgIr cm−2. At higher Ir loadings, the performance decreases at high current densities due to insufficient water transport through the catalyst layer whereas at Ir loadings <0.5 mgIr cm−2 the catalyst layer becomes inhomogeneous, which leads to a lower electrochemically active area and catalyst utilization, resulting in a significant decrease of performance. To investigate the potential for a large-scale application of PEM water electrolysis, the Ir-specific power density (gIr kW−1) for membrane electrode assemblies (MEAs) with different catalyst loadings is analyzed as a function of voltage efficiency, and the consequences regarding catalyst material requirements are discussed.

Ultralow-weight loading Ni catalyst supported on two-dimensional vermiculite for carbon monoxide methanation

Abstract Nickel-based catalysts represent the most commonly used systems for CO methanation. We have successfully prepared a Ni catalyst system supported on two-dimensional plasma-treated vermiculite (2D-PVMT) with a very low Ni loading (0.5 wt%). The catalyst precursor was subjected to heat treatment via either conventional heat treatment (CHT) or the plasma irradiation method (PIM). The as-obtained CHT-Ni/PVMT and PIM-Ni/PVMT catalysts were characterized with scanning electron microscopy (SEM), energy dispersive X-ray (EDX), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), inductively coupled plasma-atomic emission spectroscopy (ICP-AES) and high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM). Additionally, CHT-NiO/PVMT and PIM-NiO/PVMT catalysts were characterized with hydrogen temperature programmed reduction (H2-TPR). Compared with CHT-Ni/PVMT, PIM-Ni/PVMT exhibited superior catalytic performance. The plasma treated catalyst PIM-Ni/PVMT achieved a CO conversion of 93.5% and a turnover frequency (TOF) of 0.8537 s− 1, at a temperature of 450 °C, a gas hourly space velocity of 6000 ml·g− 1·h− 1, a synthesis gas flow rate of 65 ml·min− 1, and a pressure of 1.5 MPa. Plasma irradiation may provide a successful strategy for the preparation of catalysts with very low metal loadings which exhibit excellent properties.

Separation of cobalt, neodymium and dysprosium using amorphous zirconium phosphate

The purpose of this study was to investigate the separation of Co, Nd and Dy from a ternary Co-Nd-Dy solution using amorphous zirconium phosphate (am-ZrP). Am-ZrP was synthesized by a precipitation method at room temperature and subsequently characterized by Fourier transform-infrared spectrometry, thermogravimetry, scanning electron microscopy, X-ray diffraction, solid-state 31P magic angle spinning nuclear magnetic resonance spectrometry and sodium hydroxide titration (with and without background salt). The ion exchange kinetics of am-ZrP that were determined in ternary 1mM equimolar solutions at equilibrium pH2.5. The effect of pH on the adsorption was studied in ternary 1mM equimolar solutions and the uptakes of the metals increased with increasing pH until approximately pH3.5. The adsorption isotherms of Co, Nd and Dy were tested in a series of ternary equimolar solution, the total uptake amounted to 4.13meq/g at pH ~3.0. The preference of am-ZrP for these metals occurred in decreasing order Dy>Nd≫Co. The separation of Co, Nd and Dy from their 1mM equimolar ternary mixture was investigated on an am-ZrP column. Effects of loading (7.8%, 62% and 100%) on the separation were compared by measuring the corresponding HNO3 elution fractions. It was found that with a lower metal loading of 7.8%, three clear elution bands were obtained. Am-ZrP exhibited selective separation properties towards the ternary Co-Nd-Dy system, which contribute to the future scale-up studies for the recycling of NdFeB magnets.

Electrooxidation of glucose by binder-free bimetallic Pd1Ptx/graphene aerogel/nickel foam composite electrodes with low metal loading in basic medium

Many 2D graphene-based catalysts for electrooxidation of glucose involved the use of binders and toxic reducing agents in the preparation of the electrodes, which potentially causes the masking of original activity of the electrocatalysts. In this study, a green method was developed to prepare binder-free 3D graphene aerogel/nickel foam electrodes in which bimetallic Pd-Pt NP alloy with different at% ratios were loaded on 3D graphene aerogel. The influence of Pd/Pt ratio (at%: 1:2.9, 1:1.31, 1:1.03), glucose concentration (30 mM, 75 mM, 300 mM, 500 mM) and NaOH concentration (0.1 M, 1 M) on electrooxidation of glucose were investigated. The catalytic activity of the electrodes was enhanced with increasing the Pd/Pt ratio from 1:2.9 to 1:1.03, and changing the NaOH/glucose concentration from 75 mM glucose/0.1 M NaOH to 300 mM glucose/1 M NaOH. The Pd1Pt1.03/GA/NF electrode achieved a high current density of 388.59 A g−1 under the 300 mM glucose/1 M NaOH condition. The stability of the electrodes was also evaluated over 1000 cycles. This study demonstrated that the Pd1Pt1.03/GA/NF electrode could be used as an anodic electrode in glucose-based fuel cells.

Specific Recovery and In Situ Reduction of Precious Metals from Waste To Create MOF Composites with Immobilized Nanoclusters

Incorporation of active metal (especially precious metal) nanocomponents into metal–organic frameworks (MOFs) could capacitate MOFs with enhanced or new properties for innovative industrial applications. Despite increasing numbers of reports of precious metal nanoparticles/MOFs, developing such composites with low cost and high metal loading is still highly desirable. Herein, we demonstrated a novel and facile method to convert precious metal waste to wealth via using thiourea modified MOFs of UiO-66-TU as a proof of principle to recover and immobilize precious metals. The new MOFs exhibited excellent selectivity which allowed for precious metals to be isolated from the waste electronic and electrical equipment (WEEE), which commonly contain different metal species. UiO-66-TU extracts a representative precious metal of Au effectively in a wide pH range, and the maximum Au adsorption capacity could approach 326 mg g–1. Through a simple reduction treatment, the adsorbed Au ions could be converted to well-di...

Direct methanol fuel cell stack for auxiliary power units applications based on fumapem® F-1850 membrane

Direct methanol fuel cells (DMFCs) have been actively investigated from both fundamental and applied points of view due to their interesting perspectives for the application in the fields of auxiliary power supply and portable power sources. However, research efforts are still needed to solve the drawbacks presently affecting these devices, such as methanol cross-over constraints, high costs of materials, etc. The present paper addresses these issues by using a new FUMATECH proton exchange membrane (fumapem® F-1850), characterized by a nominal equivalent weight of 1800, as the electrolyte, and low electrode noble metal loadings compared to the state of the art. A membrane-electrode assembly (MEA) based on this membrane was investigated in a small area (5 cm2) direct methanol fuel cell at 60 °C and compared to a benchmark Nafion® 115 membrane in terms of performance and methanol cross-over. The F-1850 membrane showed a lower methanol cross-over rate than Nafion® 115, despite a lower thickness of the fumapem® membrane. This allowed to obtain a higher performance (74 vs. 64 mW cm−2) for the F-1850 membrane compared to Nafion® at ambient pressure. To study the scalability of the DMFC device and related components, the new membrane was integrated in large-area MEAs (100 cm2) and investigated in a 5-cell and 10-cell pressurized stack based on a bipolar design. The stack was tested at 75 °C, 5 M methanol solution at the anode and pressurized oxygen (2 atm. rel.) at the cathode, giving a normalized power density per cell of about 130 mW cm−2. The results obtained with the 10-cell stack showed a good agreement with the performance recorded with the 5-cell stack, confirming the scalability of the DMFC device.

HDO activity of carbon-supported Rh, Ni and Mo-Ni catalysts

This work reports the performance of low metal loading (about 3wt.%) Rh, Ni and Mo-Ni catalysts supported on carbon in the hydrodeoxygenation (HDO) of phenol. The catalytic tests were carried out in a flow microreactor at 310°C and at a total hydrogen pressure of 3MPa. A commercial NiMoP/γ-Al2O3 sulfided catalyst was used as reference. The effect of catalyst pre-treatment (reduction against sulfidation) was investigated in the case of the noble metal catalyst. The thermally treated in inert atmosphere, fresh reduced and spent catalysts have been characterized by several physicochemical techniques: chemical analysis, N2 adsorption-desorption isotherms, Raman spectroscopy, Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and High Resolution Transmission Electron Microscopy (HRTEM).The HDO of phenol was found to be favored on the bifunctional Rh/C and Ni/AC catalysts which exhibit a large amount of well dispersed metallic species (from HRTEM). Contrary to a commercial sulfided NiMo/Al2O3 catalyst, the hydrogenation of aromatic ring of phenol was favored being the CO bond hydrogenolysis a minor reaction route. Catalytic HDO of phenol over Rh/C reveal that the catalyst activation by reduction is advantageous compared to that by sulfidation. The partial substitution of Ni by Mo in the Mo-Ni/AC catalyst led to enhance of the catalyst stability but decrease of overall activity occurs due to the decrease of amount of metallic nickel species. The role of the MoO3 species in the inhibition of deactivation by coke is discussed.

The electrochemical activity of two binary alloy catalysts toward oxygen reduction reaction in 0.1 M KOH

The platinum group metals (Pt, Ir and Ru) and the carbide-derived carbon support with the very high specific surface area were used to synthesise the low noble metal loading Pt-C, IrPt-C and RuPt-C alloy catalysts. The alloying of the platinum group metals in the studied catalysts was proved by the several independent physical characterization methods like: the X-ray diffraction, time of flight secondary ion mass-spectrometry, X-ray photoelectron spectroscopy, scanning and transmission electron microscopy. The electrocatalytic activity toward oxygen reduction reaction of the synthesised catalysts in an alkaline solution was studied and compared with the commercially available Pt-Vulcan. The combined and detail approach using the transmission electron microscopy and inductively coupled plasma mass spectrometry for estimation of the surface area of metal particles is provided. The noticeably higher calculated mass corrected and specific kinetic current density values for Pt-C catalyst were established. For IrPt-C and RuPt-C alloy catalysts, mass corrected current density values are comparable with the commercial Pt-Vulcan. The specific kinetic current density values increase in the following sequence: RuPt-C < IrPt-C < Pt-Vulcan < Pt-C.

PWR core design with Metal Matrix Micro-encapsulated (M3) fuel

Metal Matrix Micro-encapsulated (M3) fuel consists of TRISO coated fuel particles directly dispersed in a matrix of zirconium metal to form a solid rod. In this integral fuel concept the cladding tube and the failure mechanisms associated with it have been eliminated; therefore, M3 fuel, compared to existing fuel designs, is expected to provide greatly improved operational performance. The main challenge to the deployment of M3 fuels is the low heavy metal load. This needs to be compensated with high density fuel (uranium nitride), larger rods and mainly higher enrichment. This study found that M3 fuel requires about 15.5% enriched UN TRISO particles to match the cycle length of standard fuel when loaded in a PWR. In order to achieve comparable reactivity feedbacks, in particular moderator temperature, the pitch to rod diameter ratio should be reduced to 1.20 compared to the typical 1.326. As M3 fuel provides a better path for heat transfer from the fuel, such smaller pitch is expected to be feasible, but further evaluations especially to examine thermal-hydraulic aspects are required. Analyses of possible load patterns for burnable poisons showed that M3 fuel maintains similar cycle length to that of standard fuel and pin power peaks are also comparable. Nevertheless, further optimization will be required to limit assembly power peaks.

High-Energy-Resolution X-ray Absorption Spectroscopy for Identification of Reactive Surface Species on Supported Single-Site Iridium Catalysts.

We report high-energy-resolution X-ray absorption spectroscopy detection of ethylene and CO ligands adsorbed on catalytically active iridium centers isolated on zeolite HY and on MgO supports. The data are supported by density functional theory and FEFF X-ray absorption near-edge modelling, together with infrared (IR) spectra. The results demonstrate that high-energy-resolution X-ray absorption spectra near the iridium LIII (2p3/2 ) edge provide clearly ascribable, distinctive signatures of the ethylene and CO ligands and illustrate effects of supports and other ligands. This X-ray absorption technique is markedly more sensitive than conventional IR spectroscopy for characterizing surface intermediates, and it is applicable to samples having low metal loadings and in reactive atmospheres and is expected to have an increasing role in catalysis research by facilitating the determination of mechanisms of solid-catalyzed reactions through identification of reaction intermediates in working catalysts.

Increased Affinity of Small Gold Particles for Glycerol Oxidation over Au/TiO2 Probed by NMR Relaxation Methods

The aerobic oxidation of glycerol in aqueous solution over Au/TiO2 catalysts has been studied, and the effect of Au loading by wet impregnation, in the range 0.5–5% Au, has been assessed. Low metal loading favors the deposition of smaller particles, whereas higher loadings lead to the formation of much larger gold particles, as revealed by scanning transmission electron microscopy (STEM) analysis. Reaction studies show that a higher metal loading has a detrimental effect on the catalyst activity, which decreases significantly as the Au load increases. In addition to reaction studies, 1H NMR T1/T2 relaxation time measurements have been used to assess the effect of metal loading and particle size on the adsorption properties of glycerol (reactant) and water (solvent) within the catalyst. The NMR results show that the adsorption properties of glycerol relative to water as a function of the Au loading have a similar trend to that observed for the reactivity, with glycerol exhibiting a higher surface affinity ...

Gold nanoparticle colorants as traditional ceramic glaze alternatives

AbstractHistorically, Roman stained glass has been a standard for high‐temperature color stability since biblical times but was not properly characterized as emission from nanoparticle plasmon resonance until the 1990s. The methods under which it was created have been lost, but some efforts have recently been made to recreate these properties using gold nanoparticle inks on glassy surfaces. This body of work employs gold nanoparticle systems ranging from 0.015% to 0.100% (wt/wt), suspended in a clear glaze body. The glazes are fired with traditional ceramic methods—in both gas reduction and electric oxidation kilns—in which nanoparticles are retained and can be imaged via TEM. Various colors intensities are reported in addition to changes in nanoparticle size after application and firing. The nanoparticle glazes are compared to traditional red glazes, highlighting the significantly lower metal loading required (5%‐10% for traditional glazes vs 0.100% for gold (wt/wt)), therein. Finally, proof of concept is provided with a functional gold nanoparticle mug, fired in reduction, that costs roughly 0.98$ USD in gold used.