Ruthenium Hydroxide Research Articles

Engineering Amorphous/Crystalline Ru(OH)3/CoFe-Layered Double Hydroxide for Hydrogen Evolution at 1000 mA cm-2.

For large-scale industrial applications, it is highly desirable to create effective, economical electrocatalysts with long-term stability for the hydrogen evolution reaction (HER) at a large current density. Herein, we report a unique motif with crystalline CoFe-layered hydroxide (CoFe-LDH) nanosheets enclosed by amorphous ruthenium hydroxide (a-Ru(OH)3/CoFe-LDH) to realize the efficient hydrogen production at 1000 mA cm-2, with a low overpotential of 178 mV in alkaline media. During the continuous HER process for 40 h at such a large current density, the potential remains almost constant with only slight fluctuations, indicating good long-term stability. The remarkable HER performance can be attributed to the charge redistribution caused by abundant oxygen vacancies in a-Ru(OH)3/CoFe-LDH. The increased electron density of states lowers the charge-transfer resistance and promotes the formation and release of H2 molecules. The water-splitting electrolyzer with a-Ru(OH)3/CoFe-LDH as both an anode and a cathode in 1.0 M KOH demonstrates stable hydrogen production and a 100% faradic efficiency. The design strategy of interface engineering in this work will inspire the design of practical electrocatalysts for water splitting on an industrial scale.

Sub-Second Joule-Heated RuO2-Decorated Nitrogen- and Sulfur-Doped Graphene Fibers for Flexible Fiber-type Supercapacitors.

Graphene-based fiber-shaped supercapacitors (FSSCs) have received considerable attention as potential wearable energy storage devices owing to their simple operating mechanism, flexibility, and long-term stability. To date, energy storage capacities of supercapacitors have been significantly improved via strategies such as heteroatom doping and the incorporation of pseudocapacitive metal oxides. Herein, we develop a novel and scalable direct-hybridization method that combines heteroatom doping and metal oxide hybridization for the fabrication of high-performance FSSCs. Using porous and highly conductive nitrogen and sulfur co-doped graphene fibers (NS-GFs) as self-heating units, we successfully convert ruthenium hydroxide anchored to the surface into ruthenium oxide nanoparticles after programmed sub-second electrothermal annealing without structural damage of the fibers. The resulting fibers show an increased gravimetric capacitance of 68.88 F g-1 compared to that of the pristine NS-GF (8.32 F g-1), excellent cyclic stability maintaining 96.67% of the initial capacitance after 20 000 continuous charging/discharging cycles, and good mechanical flexibility. The findings of this work advocate a successful Joule heating strategy for preparing high-performance graphene-based metal oxide hybrid FSSCs for use in energy storage applications.

Aerobic Dehydrogenative Coupling of Naphthols and Phenols with a Ru(OH)x/Al2O3 Catalyst under Continuous‐Flow Conditions

AbstractDehydrogenative coupling reactions of naphthols and phenols were achieved with a heterogeneous catalyst, alumina‐supported ruthenium hydroxide (Ru(OH)x/Al2O3), using continuous‐flow conditions and aerobic oxygen as the sole oxidant. The reactions were operated continuously for more than 16 h with good reactivity and selectivity. The Ru catalyst could be recycled at least three times by a simple online washing/activation procedure without depackaging the catalyst cartridge. The reaction provided binaphthols and biphenols as valuable products for synthetic purpose and functional materials, while an over‐oxidized quinone was obtained with 2,6‐Di‐tert‐butylphenol; combining this reaction with catalytic hydrogenation under continuous‐flow conditions enabled smooth conversion of quinone to the 4,4′‐biphenol derivative, which is a member of an important class of compounds for liquid crystals, engineering plastics, and other functional materials.

Aerobic Oxidative Cleavage of Vicinal Diol Fatty Esters by a Supported Ruthenium Hydroxide Catalyst

Oxidative cleavage of fatty acids and fatty acid derivatives can be used to obtained mono- and dicarboxylic acids, which are valuable building blocks in different industries. Although ozonolysis ha...

Catalytic Hydrolysis of Tricresyl Phosphate by Ruthenium (III) Hydroxide and Iron (III) Hydroxide towards Sensing Application.

Tricresyl phosphate (TCP) is an organophosphorous neurotoxin that has been detected in water, soil and air. Exposure to TCP in cockpit and cabin air poses a severe threat to flight safety and the health of the aircraft cabin occupants. Conventional methods for the detection of TCP in various samples are gas or liquid chromatography coupled to mass spectrometry, which are complex and expensive. To develop a simple low-cost methodology for the real-time monitoring of TCP in the environment, an effective catalyst is demanded for the hydrolysis of TCP under neutral condition. In this study, Ruthenium (III) hydroxide and Iron (III) hydroxide are found to facilitate the production of the alcoholysis and hydrolysis products of TCP, suggesting their role as a catalyst. With this finding, these metal hydroxides provide new potential to realize not only simple colorimetric or electrochemical detection of TCP, but also a simple detoxication strategy for TCP in environment. In addition, the catalytic capability of Ru (III) or Fe (III) hydroxide for TCP gives a hint that they can potentially serve as catalysts for the hydrolysis of alcolyolysis of many other organophosphate compounds.

Electrochemical Atomic Layer Etching of Ruthenium

A novel process for the electrochemical atomic layer etching (e-ALE) of ruthenium (Ru) is described. In this process, the surface Ru is electrochemically oxidized to form a monolayer of ruthenium (III) hydroxide—Ru(OH)3. The Ru(OH)3 monolayer is then selectively etched in an electrolyte containing chloride (Cl–) species. This etching process is selective towards Ru(OH)3 and does not attack the underlying Ru metal. Adsorbed Cl– on the Ru electrode is then cathodically desorbed before the sequence of Ru oxidation and Ru(OH)3 etching is repeated. This e-ALE sequence is shown to etch Ru at approximately 0.5 monolayer per cycle while practically avoiding any surface roughness amplification. The proposed Ru e-ALE process uses a single electrolyte which eliminates the need for electrode transfer or electrolyte switching between process steps. In this report, we employ electrochemical, microscopic and spectroscopic techniques to gain insights into the various characteristics of the Ru e-ALE process.

In situ electro-oxidation modulation of Ru(OH)x/Ag supported on nickel foam for efficient hydrogen evolution reaction in alkaline media

Transition metal hydroxides for hydrogen evolution reaction (HER) usually have been limited by poor intrinsic activity and weak conductivity. In our work, in situ electro-oxidation as an effective way has been used to modulate the electronic states of active sites for ruthenium hydroxides, which provides obviously enhanced activity for HER in alkaline media. Ag-modified nickel foam (NF) as substrate can provide the excellent conductivity to improve the charge transfer rate of Ru(OH)x/Ag/NF. In situ electro-oxidation process has been conducted for Ru(OH)x/Ag/NF through OER measurements in alkaline media, which results in the formation of more Ru (IV) as higher actives sites for HER. Compared to Ru(OH)x/NF, X-ray photoelectron spectroscopy (XPS) and polarization curves prove that Ag doping in Ru(OH)x/Ag/NF may contribute to the oxidization of ruthenium from Ru (III) to Ru (IV) during in situ electro-oxidation. The obtained Ru(OH)x/Ag/NF exhibits Pt-like HER activity with a very low overpotential of 103.2 mV to drive 100 mA cm−2 in 1.0 M KOH. The excellent stability of Ru(OH)x/Ag/NF has also been demonstrated. Therefore, our work provides a new strategy by modulating valence state of active sites for transition metal hydroxides for efficient HER.

Selective formation of formic acid from biomass-derived glycolaldehyde with supported ruthenium hydroxide catalysts

Ceria-supported ruthenium hydroxide catalysts, Ru(OH)x/CeO2, with micro- and nanoparticle supports were applied for selective aerobic oxidation of glycolaldehyde (GAD) to formic acid (FA) in water under mild and base-free conditions.

Frontispiece: Crystal Structure and Magnetic Properties of ϵ‐RuxFe2‐xO3 Nanosize Hard Ferrite

A new series of metal-substituted ϵ-iron oxides, ϵ-RuxFe2−xO3, nanoparticles are synthesized by sintering iron oxide hydroxide with ruthenium hydroxide in a silica matrix. RuIII selectively substitutes into the regular octahedral C site among the four non-equivalent Fe sites (A, B, C, and D site). Even a small amount of Ru substitution (less than 1% of Fe) contributes to increase the Hc value (i.e., the Hc value at 300 K increases 15% at x = 0.014). The observed increase in Hc can be understood by the large single ion magnetic anisotropy due to strong spin–orbit interaction of RuIII. More information can be found in the Communication by A. Namai and S. Ohkoshi on page 11880 ff.

Crystal Structure and Magnetic Properties of ϵ-Rux Fe2-x O3 Nanosize Hard Ferrite.

A new series of metal-substituted ϵ-iron oxides, ϵ-Rux Fe2-x O3 (x=0 (1), 0.005 (2), and 0.014 (3)) nanoparticles (average size=20 nm) is synthesized by sintering iron oxide hydroxide with ruthenium hydroxide in a silica matrix. The samples are characterized by inductively coupled plasma mass spectrometry, and energy dispersive X-ray spectroscopy (EDS) of transmission electron microscope. The X-ray diffraction pattern shows that ϵ-Rux Fe2-x O3 has an orthorhombic crystal structure with a space group of Pna21 and the Rietveld analyses show that Ru is doped selectively at the regular octahedral C site among the four non-equivalent Fe sites (A, B, C, and D site). Magnetization vs. temperature plots show that the Curie temperature (TC ) depends on x, and TC =498 K for 1, 497 K for 2, and 496 K for 3. Magnetization vs. external magnetic field plots indicate that the coercive field (Hc ) increases from 17.7 kOe (1) to 20.3 kOe (3). This increment of 15 % on Hc is attributed to the single ion anisotropy of the magnetic spin on RuIII (4d5 , S=1/2).

Mechanism of Alcohol-Water Dehydrogenative Coupling into Carboxylic Acid Using Milstein's Catalyst: A Detailed Investigation of the Outer-Sphere PES in the Reaction of Aldehydes with an Octahedral Ruthenium Hydroxide.

In aqueous basic media, the square-pyramidal complex [Ru(PNN)(CO)(H)] (1-Ru, where PNN is a dearomatized bipyridyl-CH-P(t)Bu2 pincer ligand) catalyzes the transformation of alcohols and water into carboxylates and H2. A previous theoretical investigation reported the following mechanism for the reaction: (i) metal-catalyzed dehydrogenation of the alcohol into an aldehyde, (ii) metal-ligand cooperation (MLC) addition of water to 1-Ru to give an octahedral ruthenium hydroxide (2-Ru-OH), (iii) concerted MLC hydration of the aldehyde by 2-Ru-OH to give separated 1-Ru and a gem-diol, and (iv) concerted MLC dehydrogenation of the gem-diol by 1-Ru into an octahedral ruthenium dihydride (2-Ru-H) and a carboxylic acid. We calculate the outer-sphere PES in the reaction between the aldehyde and 2-Ru-OH to start with a localized coupling step yielding an ion-pair minimum (7-ip-OH) in which the hydroxyl group of an α-hydroxyl-alkoxide (gem-diolate) is coordinated to the metal of a cationic square-pyramidal complex. From 7-ip-OH, we identify a route to carboxylic acid that circumvents ligand deprotonation involving (i) 1,1-rearrangement of the gem-diolate within the contact ion pair through an α-OH/O(-) slippage TS into the octahedral 2-Ru-OCH(OH)R and (ii) a second 1,1-rearrangement through an α-O(-)/H slippage TS that gives a new ion-pair minimum in which the α-hydrogen of the anion is coordinated to the metal, followed by a localized hydride-transfer TS that gives a carboxylic acid and the octahedral hydride complex (2-Ru-H). The net transformation from 2-Ru-OH and the aldehyde to the carboxylic acid and 2-Ru-H can be viewed as a H/OH metathesis in which a hydride and a hydroxide are exchanged between the acyl group of the aldehyde and the metal center of 2-Ru-OH. The MLC mechanism gives the same metathesis products through the intermediacy of a gem-diol. When the SMD solvent continuum model is applied during geometry optimization with water as the solvent, the Gibbs free energy profile of the slippage pathway is predicted to be much lower than that predicted for MLC. The possibility of dissociation of the ion pair 7-ip-OH into free ions and reassociation is also briefly addressed. Some calculations are also performed to address why no esters are observed in the given system.

Ruthenium hydroxide supported on activated alumina for catalytic permanganate oxidation of aniline

Ruthenium loaded on CeO2 or TiO2 has been proved to be effective catalysts in permanganate oxidation, but the small size of supports led to a difficult separation of catalysts from the aqueous solution. Therefore, ruthenium hydroxide supported on activated alumina (diameter 3–4 mm), i.e. Ru-AA, was synthesized and employed as catalyst in permanganate oxidation of aniline at circumneutral pH for the first time. The characterization for Ru-AA by SEM-EDAX proved the existence of Ru on the surface of AA, but XRD patterns for AA were not affected by the impregnation of ruthenium hydroxide, due to its low concentration, low crystallinity, and good dispersion. Acting as an electron shuttle, Ru-AA significantly improved the apparent second-order rate constant (kapp) of aniline oxidation from 10.3 to 18.9 M−1 s−1 with its concentration increasing from 0.55 to 2.2 g L−1. Aniline degradation in catalytic oxidation was markedly influenced by pH, and the kapp decreased from 314.3 to 3.3 M−1 s−1 with increasing pH from 4.0 to 9.0. The intermediates of aniline in the catalytic permanganate oxidation were determined by LC–MS/MS analysis. Ru-AA displayed an excellent stability in first 10 consecutive runs, and the regenerated Ru-AA showed a better performance than the spent one after 15 runs, but less catalytic capability than the virgin one due to the leaching of Ru. The schematic mechanism for Ru-AA-catalyzed permanganate oxidation of aniline was proposed finally.

Ruthenium hydroxide supported on magnetic nanoparticles: a benign aqueous protocol for hydration of nitriles

Ruthenium hydroxide supported on magnetic nanoparticles: a benign aqueous protocol for hydration of nitriles

ChemInform Abstract: Development of Highly Active Heterogeneous Oxidation Catalysts Based on the Properties of Metal Hydroxides

AbstractReview: 62 refs.

Intramolecular C-H/O-H bond cleavage with water and alcohol using a phosphine-free ruthenium carbene NCN pincer complex.

Transition metal complexes that exhibit metal-ligand cooperative reactivity could be suitable candidates for applications in water splitting. Ideally, the ligands around the metal should not contain oxidizable donor atoms, such as phosphines. With this goal in mind, we report new phosphine-free ruthenium NCN pincer complexes with a central N-heterocyclic carbene donor and methylpyridyl N-donors. Reaction with base generates a neutral, dearomatized alkoxo-amido complex, which has been structurally and spectroscopically characterized. The tert-butoxide ligand facilitates regioselective, intramolecular proton transfer through a CH/OH bond cleavage process occurring at room temperature. Kinetic and thermodynamic data have been obtained by VT NMR experiments; DFT calculations support the observed behavior. Isolation and structural characterization of a doubly dearomatized phosphine complex also strongly supports our mechanistic proposal. The alkoxo-amido complex reacts with water to form a dearomatized ruthenium hydroxide complex, a first step towards phosphine-free metal-ligand cooperative water splitting.

Catalytic transfer hydrogenation of levulinate esters to γ-valerolactone over supported ruthenium hydroxide catalysts

Production of γ-valerolactone (GVL) from levulinate esters and several alcohols as hydrogen donors via a catalytic transfer hydrogenation (CTH) process was performed over supported ruthenium hydroxide catalysts. Among the catalysts examined, Ru(OH)x supported on high-surface-area, anatase TiO2 containing highly-dispersed ultrasmall Ru(OH)x nano-clusters was found to be the most active catalyst, which converted levulinate esters to GVL in an almost quantitative yield under mild reaction conditions with low catalyst loading. Addition of heterogeneous bases could afford a faster reaction rate in GVL production by accelerating the following intramolecular dealcoholation step. The catalyst was reusable over repeated catalytic cycles without loss of catalytic performance, making this material a potential candidate for efficient GVL production under ambient reaction conditions.

Multiphase catalytic oxidation of alcohols over paper-structured catalysts with micrometer-size pores

Paper-structured catalysts were prepared using ceramic fibers by a wet papermaking technique, followed by the deposition of ruthenium hydroxide on the fiber-network microstructures. As-prepared flexible paper catalysts possessed large geometric surface areas with micrometer-size pores. The paper-structured catalysts exhibited high catalytic efficiency for selective aerobic oxidation of aromatic and aliphatic alcohols to their corresponding aldehydes and ketones, in a fixed bed multiphase reactor. Hydrodynamic behavior in the reactor filled with either paper or bead catalysts was evaluated by measuring the residence time distribution in a cold flow model. It was revealed that the paper composites exhibited good wettability and internal diffusion of liquid substances compared with ceramic beads, showing heterogeneous liquid flow. Efficient catalytic oxidation of various alcohols was achieved using the paper-structured catalysts because uniform fluid dynamic behavior formed a thin liquid layer on the catalyst surfaces, possibly resulting in favorable gas–liquid–solid interfaces.

Development of Highly Active Heterogeneous Oxidation Catalysts Based on the Properties of Metal Hydroxides

This manuscript summarizes our recent research results on heterogeneously catalyzed aerobic oxidation reactions using supported metal hydroxide catalysts. Metal hydroxide species possess both Lewis acid and Bronsted base sites on the same metal sites, and various kinds of substrates including alcohols, primary amines, nitriles, and terminal alkynes can be activated by the concerted action of the Lewis acid and Bronsted base pair sites. In the presence of a supported ruthenium hydroxide catalyst (Ru(OH) x /Al2O3), oxidative dehydrogenation of alcohols and primary amines efficiently proceeds to afford the corresponding carbonyl compounds (aldehydes and ketones) and nitriles, respectively. In the presence of ammonia (THF solution), Ru(OH) x /Al2O3 can catalyze ammoxidation of primary alcohols to the corresponding nitriles. This ammoxidation proceeds through the sequential reactions of oxidative dehydrogenation of primary alcohols to aldehydes, dehydrative condensation of the aldehydes with ammonia to aldimines, and oxidative dehydrogenation of the aldimines. In addition, formal α-oxygenation of primary amines to the corresponding primary amides can be realized through the Ru(OH) x /Al2O3-catalyzed oxidative dehydrogenation and nitrile hydration. Moreover, a supported copper hydroxide species on a manganese oxide-based octahedral molecular sieve (Cu(OH) x /OMS-2) can act as an efficient and highly durable heterogeneous catalyst for oxidative homocoupling of terminal alkynes to the corresponding diynes. The catalyses for the above-mentioned oxidation reactions are truly heterogeneous, and the catalysts can be reused several times with keeping their high catalytic performance.

Preparation of porous paper composites with ruthenium hydroxide and catalytic alcohol oxidation in a multiphase gas–liquid–solid reaction

Abstract In situ synthesis of ruthenium hydroxide catalysts on a microporous fiber-network structure of ceramic paper composites was achieved. The efficient catalytic oxidation of alcohol was investigated in a heterogeneous, multiphase gas–liquid–solid reaction. A simple papermaking technique and subsequent immersion in a ruthenium chloride solution allowed us to fabricate novel-concept microstructured catalysts. The paper-structured catalysts possess micropores ca. 30 μm in diameter with high porosity of ca. 90%. They exhibited much higher catalytic efficiency in the O 2 -mediated oxidation in toluene of benzyl alcohol to benzaldehyde in a fixed bed external loop reactor, as compared with conventional pellet- and bead-type solid catalysts. This excellent catalytic effect is possibly attributed to the porous paper composite microstructure like microreactors.

Synthesis and Catalytic Applications of Ruthenium(0) Nanoparticles in Click Chemistry

Here we report a facile synthesis of ruthenium (Ru) Nanoparticles (NPs) by chemical co-precipitation method. The calcination of ruthenium hydroxide samples at <TEX>$500^{\circ}C$</TEX> under hydrogen atmosphere lead to the formation of <TEX>$Ru^0$</TEX> NPs. The size and aggregation of Ru NPs depends on the pH of the medium, and type of surfactant and its concentration. The X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope image (TEM) analyses of particles indicated the formation of <TEX>$Ru^0$</TEX> NPs, and have 10 to 20 nm sizes. As-synthesized <TEX>$Ru^0$</TEX> NPs are characterized and investigated their catalytic ability in click chemistry (azidealkyne cycloaddition reactions), showing good results in terms of reactivity. Interestingly, small structural differences in triazines influence the catalytic activity of <TEX>$Ru^0$</TEX> nanocatalysts. Click chemistry has recently emerged to become one of the most powerful tools in drug discovery, chemical biology, proteomics, medical sciences and nanotechnology/nanomedicine. In addition, preliminary tests of recycling showed good results with neither loss of activity or significant precipitation.