XPS and reactivity study of bimetallic nanoparticles containing Ru and Pt supported on a gold disk

Pd-Pt-Ru nanozyme with peroxidase-like activity for the detection of total antioxidant capacity

The design of highly active nanozymes and the establishment of ultra-sensitive bioassays remain a challenge. Therefore, it is necessary to synthesize highly active nanozymes. In this work, a Pd-Pt-Ru (PPR) nanozyme was prepared by atomic coating of the bimetallic nanozyme Pd-Pt. The steady-state kinetics showed that the PPR nanozyme had excellent peroxidase-like activity. Based on this concept, the as-prepared PPR nanozyme was applied to the detection of ascorbic acid (AA) and hydrogen peroxide (H₂O₂). The linear ranges for ascorbic acid and hydrogen peroxide were 2-12 μM and 5-40 mM, respectively. The limits of detection (LOD) are 1.13 μM and 2.79 mM, respectively. Ascorbic acid was used as a typical model to assay the total antioxidant capacity (TAC) of foods and several herbs. The Fructus Corni extract showed the highest reducing ability. The corresponding extracts were applied for the green synthesis of silver nanoparticles with a size of 167 nm. This study provides a method for the design of highly active nanozymes and the expansion of their applications.

Multifunctional Material Composed of Cesium Salt of Keggin-Type Heteropolytungstate and PtRh/Vulcan Nanoparticles for Electrochemical Oxidation of 2-Propanol in Acidic Medium

Platinum–rhodium nanoparticles modified with cesium salt of phosphotungstic acid, CsPTA, have been tested for electro-oxidation of 2-propanol in acidic medium. The resulting Pt-based nanoparticle-containing materials have been carried out using X-ray diffraction (XRD), microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and different electrochemical techniques combining with differential electrochemical mass spectrometry (DEMS). The experimental results such as cyclic voltammetry and chronoamperometry exhibit that films on carbon electrodes composed of CsPTA-modified PtRh/Vulcan nanoparticles improve the catalytic activity, in terms of potential and current densities recorded during electro-oxidation of 2-propanol, relative to the CsPTA-free PtRh/Vulcan nanoparticles. Particularly, the boost in the catalytic current densities is observed at low potential value (below 0.25 V vs. RHE). The differential electrochemical mass spectrometry measurements were utilized to recognize the reaction intermediates as well as products created during the electro-oxidation of 2-propanol. The results indicate that contributions from a straightforward oxidation of 2-propanol to CO2 are small in comparison to acetone yield.

A magnetically separable and recyclable g-C3N4/Fe3O4/porous ruthenium nanocatalyst for the photocatalytic degradation of water-soluble aromatic amines and azo dyes

Herein, we present the development of a visible-light-driven magnetically retrievable nanophotocatalyst made of porous ruthenium nanoparticles supported on magnetic carbon nitride (g-C3N4/Fe3O4/p-RuNP) for the facile removal/degradation of aromatic amines and azo dyes from wastewater. Aromatic amines and azo-based dyes in water bodies are highly toxic and carcinogenic even at very low concentrations and are difficult to separate because of their high solubility. Our nanocatalyst can efficiently degrade/decompose the aromatic amines and azo dyes under visible light (LED/sunlight) at room temperature and in a wide pH range (pH 5.0-9.0) without using any external chemicals. The magnetic property of the nanocatalyst facilitates its efficient and facile separation from the reaction mixture for reuse in multiple photocatalytic cycles. The nanocatalyst-based degradation of azo dyes and aromatic amines presented here is simple and convenient in terms of efficiency, energy, reusability and cost. The process also does not require any external chemicals and forms gaseous/less harmful end products.

One-Pot Process for Hydrodeoxygenation of Lignin to Alkanes Using Ru-Based Bimetallic and Bifunctional Catalysts Supported on Zeolite Y

The synthesis of high-efficiency and low-cost catalysts for hydrodeoxygenation (HDO) of waste lignin to advanced biofuels is crucial for enhancing current biorefinery processes. Inexpensive transition metals, including Fe, Ni, Cu, and Zn, were severally co-loaded with Ru on HY zeolite to form bimetallic and bifunctional catalysts. These catalysts were subsequently tested for HDO conversion of softwood lignin and several lignin model compounds. Results indicated that the inexpensive earth-abundant metals could modulate the hydrogenolysis activity of Ru and decrease the yield of low-molecular-weight gaseous products. Among these catalysts, Ru-Cu/HY showed the best HDO performance, affording the highest selectivity to hydrocarbon products. The improved catalytic performance of Ru-Cu/HY was probably a result of the following three factors: (1) high total and strong acid sites, (2) good dispersion of metal species and limited segregation, and (3) high adsorption capacity for polar fractions, including hydroxyl groups and ether bonds. Moreover, all bifunctional catalysts proved to be superior over the combination catalysts of Ru/Al₂ O₃ and HY zeolite.

Moderate oxidation levels of Ru nanoparticles enhance molecular oxygen activation for cross-dehydrogenative-coupling reactions via single electron transfer

Ruthenium nanoparticles with altered surface oxidation states showed a volcano shaped relationship in molecular oxygen activation via single electron transfer for cross-dehydrogenative-coupling reactions.

Bimetallic Nickel/Ruthenium Catalysts Synthesized by Atomic Layer Deposition for Low-Temperature Direct Methanol Solid Oxide Fuel Cells

Nickel and ruthenium bimetallic catalysts were heterogeneously synthesized via atomic layer deposition (ALD) for use as the anode of direct methanol solid oxide fuel cells (DMSOFCs) operating in a low-temperature range. The presence of highly dispersed ALD Ru islands over a porous Ni mesh was confirmed, and the Ni/ALD Ru anode microstructure was observed. Fuel cell tests were conducted using Ni-only and Ni/ALD Ru anodes with approximately 350 μm thick gadolinium-doped ceria electrolytes and platinum cathodes. The performance of fuel cells was assessed using pure methanol at operating temperatures of 300-400 °C. Micromorphological changes of the anode after cell operation were investigated, and the content of adsorbed carbon on the anode side of the operated samples was measured. The difference in the maximum power density between samples utilizing Ni/ALD Ru and Pt/ALD Ru, the latter being the best catalyst for direct methanol fuel cells, was observed to be less than 7% at 300 °C and 30% at 350 °C. The improved electrochemical activity of the Ni/ALD Ru anode compared to that of the Ni-only anode, along with the reduction of the number of catalytically active sites due to agglomeration of Ni and carbon formation on the Ni surface as compared to Pt, explains this decent performance.

High-activity mesoporous Pt/Ru catalysts for methanol oxidation

High activity mesoporous Pt/Ru catalysts with 2D-hexagonal structure were synthesized using a triblock poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) copolymer (Pluronic F127) template. The normalized mass activities for the methanol oxidation reaction (MOR) of the Pt/Ru catalysts with a regular array of pores is higher than those reported for nanoparticulated Pt/Ru catalysts. Different kinetic parameters, as Tafel slope and activation energy, were obtained for the MOR on the mesoporous catalysts. Results indicated that catalysts performance depends on pore size. Mass activities and the CO2 conversion efficiency for large pore size mesoporous catalysts (10 nm) are greater than those reported for smaller pore size mesoporous catalysts with similar composition. The effect of pore size on catalysts performance is related to the greater accessibility of methanol to the active areas inside large pores. Consequently, the overall residence time of methanol increases as compared with mesoporous catalyst with small pores.

Effect of surface segregation on the methanol oxidation reaction in carbon-supported Pt-Ru alloy nanoparticles

Ru and Pt-Ru (Pt:Ru = 1:1) nanoparticles supported on carbon black were prepared by the borohydride reduction method using oleylamine as a stabilizer in an anhydrous ethanol solvent. We investigated the effect of Pt segregation to the surface of alloy nanoparticles on the methanol oxidation reaction (MOR). As-prepared Pt(1)Ru(1)/C showed a narrow size distribution and a relatively uniform particle distribution on a carbon support. However, its electrocatalytic activity toward the MOR was poor due to the high surface concentration of Ru. As duration time of heat treatment at 200 degrees C was increased up to 2 h, the surface composition of Pt atoms was increased without significant particle growth due to thermally induced segregation of Pt atoms, which were revealed by TEM images, X-ray photoelectron spectroscopy (XPS) analysis, changes in the potentials of zero total charge (pztc), and increase in the oxidation charge of "reduced CO(2)". In particular, from the combination of CO adlayer oxidation and "reduced CO(2)" oxidation charges, the increased surface concentration of Pt of alloy catalysts was relatively quantified when compared to its as-prepared state. Cyclic voltammograms in 0.1 M HClO(4) solution with 0.5 M methanol showed that Pt(1)Ru(1)/C annealed for 2 h at 200 degrees C in a flow of mixture gas of Ar and H(2) (5 vol %) had a less positive onset potential for the MOR. These results demonstrate a definitive contribution from segregation of Pt atoms to the MOR activity.

Structural and architectural evaluation of bimetallic nanoparticles: a case study of Pt-Ru core-shell and alloy nanoparticles

A comprehensive structural/architectural evaluation of the PtRu (1:1) alloy and Ru@Pt core-shell nanoparticles (NPs) provides spatially resolved structural information on sub-5 nm NPs. A combination of extended X-ray absorption fine structure (EXAFS), X-ray absorption near edge structure (XANES), pair distribution function (PDF) analyses, Debye function simulations of X-ray diffraction (XRD), and field emission transmission electron microscopy/energy dispersive spectroscopy (FE-TEM/EDS) analyses provides complementary information used to construct a detailed picture of the core/shell and alloy nanostructures. The 4.4 nm PtRu (1:1) alloys are crystalline homogeneous random alloys with little twinning in a typical face-centered cubic (fcc) cell. The Pt atoms are predominantly metallic, whereas the Ru atoms are partially oxidized and are presumably located on the NP surface. The 4.0 nm Ru@Pt NPs have highly distorted hcp Ru cores that are primarily in the metallic state but show little order beyond 8 A. In contrast, the 1-2 monolayer thick Pt shells are relatively crystalline but are slightly distorted (compressed) relative to bulk fcc Pt. The homo- and heterometallic coordination numbers and bond lengths are equal to those predicted by the model cluster structure, showing that the Ru and Pt metals remain phase-separated in the core and shell components and that the interface between the core and shell is quite normal.

Methanol electrooxidation on PtRu bulk alloys and carbon-supported PtRu nanoparticle catalysts: a quantitative DEMS study

Methanol electrooxidation on smooth Pt and PtRu bulk alloys and carbon-supported Pt and PtRu nanoparticle catalysts has been studied using cyclic voltammetry and potential step chronoamperometry combined with differential electrochemical mass spectrometry (DEMS). The current efficiencies for generated CO2 and methyl formate were calculated from Faradaic current (coulometric charge) and mass spectrometric currents (charges) at m/z=44 and m/z=60. The effects of Ru content in PtRu catalysts, catalyst loading/roughness, and the concentration of sulfuric acid as supporting electrolyte on the reaction kinetics and product distribution during methanol electrooxidation have been investigated. The results indicate that Pt-rich PtRu alloys and carbon-supported PtRu catalysts with ca. 20 atom % Ru content exhibit the highest catalytic activity for methanol electrooxidation, that is, the highest Faradaic current and the highest current efficiency for CO2 generation at low applied potentials. As the catalyst loading/roughness increases, the current efficiency for CO2 formation increases due to the further oxidation of soluble intermediates (formaldehyde and formic acid). At high concentrations of sulfuric acid, the electrooxidation of methanol was suppressed; both the oxidative current and the current efficiency of CO2 decreased, likely due to sulfate/bisulfate adsorption.

Ru-Pt core-shell nanoparticles for preferential oxidation of carbon monoxide in hydrogen

Most of the world's hydrogen supply is currently obtained by reforming hydrocarbons. 'Reformate' hydrogen contains significant quantities of CO that poison current hydrogen fuel-cell devices. Catalysts are needed to remove CO from hydrogen through selective oxidation. Here, we report first-principles-guided synthesis of a nanoparticle catalyst comprising a Ru core covered with an approximately 1-2-monolayer-thick shell of Pt atoms. The distinct catalytic properties of these well-characterized core-shell nanoparticles were demonstrated for preferential CO oxidation in hydrogen feeds and subsequent hydrogen light-off. For H2 streams containing 1,000 p.p.m. CO, H2 light-off is complete by 30 (composite function)C, which is significantly better than for traditional PtRu nano-alloys (85 (composite function)C), monometallic mixtures of nanoparticles (93 (composite function)C) and pure Pt particles (170 ( composite function)C). Density functional theory studies suggest that the enhanced catalytic activity for the core-shell nanoparticle originates from a combination of an increased availability of CO-free Pt surface sites on the Ru@Pt nanoparticles and a hydrogen-mediated low-temperature CO oxidation process that is clearly distinct from the traditional bifunctional CO oxidation mechanism.

Structures and catalytic properties of PtRu electrocatalysts prepared via the reduced RuO2 nanorods array

Structures and properties of PtRu electrocatalyts, derived from the aligned RuO2 nanorods (RuO2NR), are investigated using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and cyclic voltammetry toward COads and methanol oxidation. The catalytic activity of methanol oxidation and the CO tolerance are promoted significantly by reducing RuO2 into Ru metal before decorating with Pt. Reduction of RuO2NR was carried out by either thermal decomposition at 650 degrees C in vacuum or H2-reduction at 130 degrees C in low-pressure hydrogen. Reduction assisted by hydrogen allows infiltrating decomposition at low temperature and produces an array of nanorods with rugged walls featuring small Ru nuclei and larger surface area. Pt-RuNR, whose surface Pt:Ru ratio=0.58:0.42 was prepared by decorating with 0.1 mg cm(-2) Pt on the H2-reduced array containing 0.39 mg cm(-2) Ru, demonstrates a favorable combination of CO tolerance and high methanol oxidation activity superior to other RuO2NR-derived catalysts. When compared with a commercial electrocatalyst of PtRu (1:1) alloy (<4 nm), the activity of Pt-RuNR in methanol oxidation is shown to be somewhat lower at potential<0.48 V and higher at potential>or=0.48 V.

Electrocatalysis of oxygen reduction and small alcohol oxidation in alkaline media

We present here a critical review of several technologically important electrocatalytic systems operating in alkaline electrolytes. These include the oxygen reduction reaction (ORR) occurring on catalysts containing Pt, Pd, Ir, Ru, or Ag, the methanol oxidation reaction (MOR) occurring on Pt-containing catalysts, and the ethanol oxidation reaction (EOR) occurring on Ni-Co-Fe alloy catalysts. Each of these catalytic systems is relevant to alkaline fuel cell (AFC) technology, while the ORR systems are also relevant to chlor-alkali electrolysis and metal-air batteries. The use of alkaline media presents advantages both in electrocatalytic activity and in materials stability and corrosion. Therefore, prospects for the continued development of alkaline electrocatalytic systems, including alkaline fuel cells, seem very promising.

Generation and Detection of Single Metal Nanoparticles Using Scanning Electrochemical Microscopy Techniques

Different pathways towards the generation and detection of a single metal nanoparticle (MNP) on a conductive carbon support for testing as an electrocatalyst are described. Various approaches were investigated including interparticle distance enhancement, electrochemical and mechanical tip-substrate MNP transfer onto macroscopic surfaces, scanning electrochemical microscopy (SECM)-controlled electrodeposition, and the use of selective binding monolayers on carbon fiber electrodes (CFEs) for solution-phase-selective adsorption. A novel SECM technique for electrodepositing MNPs on CFE tips immersed 100-200 nm below the electrolyte level was developed and used to generate single Pt and Ni nanoparticles. Following their generation, we demonstrate electrocatalytic detection of Fe3+ on individual Pt particles with the CFE in a Fe3+/H2SO4 solution. We also describe an approach of attaching MNPs to CFEs by controlling the composition of monolayers bonded to the CFE. By employing a monolayer with a low ratio of binding (e.g., 4-aminopyridine) to nonbinding molecules (e.g., aniline) and controlling the position of the CFE in a colloidal Pt solution with a SECM, we attached a single 15 nm radius Pt nanoparticle to the CFE. Such chemisorbed Pt particles exhibited a stronger adhesion on surface-modified CFEs and better mechanical stability during proton reduction than MNPs electrodeposited directly on the CFE.

Size Effects in Electronic and Catalytic Properties of Unsupported Palladium Nanoparticles in Electrooxidation of Formic Acid

We report a combined X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), and chronoamperometry (CA) study of formic acid electrooxidation on unsupported palladium nanoparticle catalysts in the particle size range from 9 to 40 nm. The CV and CA measurements show that the most active catalyst is made of the smallest (9 and 11 nm) Pd nanoparticles. Besides the high reactivity, XPS data show that such nanoparticles display the highest core-level binding energy (BE) shift and the highest valence band (VB) center downshift with respect to the Fermi level. We believe therefore that we found a correlation between formic acid oxidation current and BE and VB center shifts, which, in turn, can directly be related to the electronic structure of palladium nanoparticles of different particle sizes. Clearly, such a trend using unsupported catalysts has never been reported. According to the density functional theory of heterogeneous catalysis, and mechanistic considerations, the observed shifts are caused by a weakening of the bond strength of the COOH intermediate adsorption on the catalyst surface. This, in turn, results in the increase in the formic acid oxidation rate to CO2 (and in the associated oxidation current). Overall, our measurements demonstrate the particle size effect on the electronic properties of palladium that yields different catalytic activity in the HCOOH oxidation reaction. Our work highlights the significance of the core-level binding energy and center of the d-band shifts in electrocatalysis and underlines the value of the theory that connects the center of the d-band shifts to catalytic reactivity.