Ruthenium Clusters Research Articles

Selective oxidation of C (sp3)—H bonds enabled by ruthenium clusters containing pyridine‐alkoxide ligands

Reactions of Ru3(CO)12 with 6‐methyl‐2‐pyridinyl‐ethanol ligands 6‐CH3‐2‐PyCH2CR1R2OH [R1H, R22‐CH3OC6H4 (L1H); R1H, R22‐CF3C6H4 (L2H); R1R2CH3 (L3H); and R1H, R22,6‐(CH3O)2C6H3 (L4H)] in refluxing THF afforded the corresponding trinuclear ruthenium clusters (6‐CH3‐2‐PyCH2CR1R2O)(μ2‐H)Ru3(CO)9 [R1H, R22‐CH3OC6H4 (1); R1H, R22‐CF3C6H4 (2); R1R2CH3 (3); and R1H, R22,6‐(CH3O)2C6H3 (4)], respectively. All the four new clusters were well characterized by elemental analysis, IR, 1H, and 13C nuclear magnetic resonance. Furthermore, their crystal structures were determined by single‐crystal X‐ray diffraction analysis. The ruthenium clusters were proved to be efficient catalysts for the oxidation of saturated CH bonds with tert‐butyl hydroperoxide (TBHP) as the oxidant in CH3CN/H2O (1:4) at room temperature.

Trimeric Ruthenium Cluster-Derived Ru Nanoparticles Dispersed in MIL-101(Cr) for Catalytic Transfer Hydrogenation

The synthesis of highly dispersed metal nanoparticles supported on metal–organic frameworks has been widely studied as a means to provide high-performance heterogeneous catalysts. Here, a Ru-nanoparticles-supported MIL-101(Cr) catalyst was prepared via a diamine and oxo-centered trimeric ruthenium cluster ([Ru3(μ3-O)(μ-CH3COO)6(H2O)3]CH3COO), Ru3 cluster sequential grafting, followed by alcohol reduction. Ethylenediamine (ED) acted as the linker, coordinating with unsaturated sites on both MIL-101(Cr) and the Ru3 cluster to produce Ru3-ED-MIL-101(Cr), after which selective alcohol reduction process provided the Ru/ED-MIL-101(Cr) catalyst. The synthesized Ru/ED-MIL-101(Cr) catalyst contained small, finely dispersed Ru nanoparticles, and the structural integrity of ED-MIL-101(Cr) was maintained. The Ru/ED-MIL-101(Cr) catalyst was tested for the transfer hydrogenation of benzene using isopropanol as the hydrogen source, where it was shown to outperform other Ru-based catalysts.

Ultrafine Ruthenium Clusters Shell-Embedded Hollow Carbon Spheres as Nanoreactors for Channel Microenvironment-Modulated Furfural Tandem Hydrogenation.

Rationally modulating the catalytic microenvironment is important for targeted induction of specific molecular behaviors to fulfill complicated catalytic purposes. Herein, a metal pre-chelating assisted assembly strategy is developed to facilely synthesize the hollow carbon spheres with ultrafine ruthenium clusters embedded in pore channels of the carbon shell (Ru@Shell-HCSs), which can be employed as nanoreactors with preferred electronic and geometric catalytic microenvironments for the efficient tandem hydrogenation of biomass-derived furfural toward 2-methylfuran. The channel-embedding structure is proved to confer the ultrafine ruthenium clusters with an electron-deficient property via a reinforced interfacial charge transfer mechanism, which prompts the hydrogenolysis of intermediate furfuryl alcohol during the tandem reaction, thus resulting in an enhanced 2-methylfuran generation. Meanwhile, lengthening the shell pore channel can offer reactant molecules with a prolonged diffusion path, and correspondingly a longer retention time in the channel, thereafter delivering an accelerated tandem hydrogenation progression. This paper aims to present a classic case that emphasizes the critical role of precisely controlling the catalytic microenvironment of the metal-loaded hollow nanoreactors in coping with the arduous challenges from multifunctional catalyst-driven complex tandem reactions.

SYNTHESIS AND PROPERTIES OF RUTHENIUM CLUSTER COMPLEXES

Methods for the synthesis of ruthenium cluster complexes based on carbonyl and amine-containing organic bifunctional ligands have been developed. The structure of the obtained combinations of clusters were determined on the basis of IR spectroscopy data, thermogravimetry, and elemental analysis. Samples of ligands I and II were obtained by condensation of carboxylic acid chlorides of cyclopentane and cyclohexane with ethylene followed by replacement of the chlorine atom by amine groups. To obtain cluster complexes of ruthenium with the synthesized ligands the ruthenium trichloride salt (RuCl3) was dissolved in water, and the calculated amount of sodium borohydride was added in portions to the resulting solution under vigorous stirring in nitrogen atmosphere. Rapidly emerging black-dispersed nanoparticles of metallic ruthenium did not precipitate. When organic ligands I and II are added, the corresponding cluster compounds III and IV are formed, which gradually over 45 min. precipitated from an aqueous solution. The resulting dark-brown precipitates were washed with distilled water and dried in a nitrogen atmosphere at a temperature of 35-400C. The melting temperatures of the synthesized compounds were determined, the components for cluster III - 2060С and cluster IV - 2220С (with decomposition). The IR spectra of cluster compounds show intense absorption bands characterizing the presence of both the ketone carbonyl group and the amine fragment. The absorption bands of ketone groups in cluster compounds are shifted towards higher frequencies compared to the initial ligands. A similar picture is also observed when comparing the IR vibrations of CN bonds in the initial ligands and the corresponding cluster compounds. The results of elemental analysis confirm the structures of cluster compounds and are in complete agreement with the concept that cluster compounds are formed upon the reduction of ruthenium salts with metal hydrides in an aqueous solution. Apparently, in this case, the most stable ruthenium clusters with tetrahedral structure are formed.. Thermogravimetric analysis made it possible to establish the presence of a peak at a temperature of 3180C with a mass number of 744.8 , corresponding to a cluster combination of four ruthenium atoms. At each stage of decomposition, the experimental mass losses are in good agreement with the calculated values. Keywords: synthesis, ruthenium, cluster complexes, amine and caryonyl containing ligands, bifunctional ligands, cyclopentyl amino ketone, cyclohexyl amino ketone.

Supported Ru Single Atoms and Clusters on P‐Doped Carbon Nitride as an Efficient Photocatalyst for H2O2 Production

AbstractPhotocatalytic H2O2 evolution via two‐electron oxygen reduction is a promising path for renewable and on‐the‐spot H2O2 production compared with the traditional anthraquinone method. However, the efficiency of photocatalytic production of H2O2 is usually very low. Herein, P‐doped carbon nitride loaded with ruthenium single atoms and clusters (Ruatom/P‐CN) is reported as an efficient photocatalyst for H2O2 production. The yield of H2O2 over Ruatom/P‐CN (385.8 mmol g−1 h−1) is about 4.3 times higher than that of P‐CN (88.9 mmol g−1 h−1) and 3.6 times higher than that of ruthenium nanoparticles loaded P‐CN (105.9 mmol g−1 h−1). Further mechanistic study indicates that the presence of Ru in the form of single atoms and clusters not only improves the separation efficiency of photogenerated carriers and inhibits the recombination of photogenerated electron‐hole pairs, but also increases the reactive sites of this catalytic system. This study breaks through people‘s understanding that precious metal loading is not conducive to H2O2 selectivity and provides a new way to prepare low‐metal loading, high‐activity photocatalysts for H2O2 production.

Integrating trace ruthenium cluster with cobalt boride toward superior overall water splitting in neutral media

Cobalt boride which is an active bifunctional water splitting catalyst in alkaline media shows poor activity in neutral media. We found that trace ruthenium (Ru) cluster deposition (80 μg·cm−2) on cobalt boride by simple wet chemical reduction method can dramatically improve both its hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) activity in neutral solution. The electron transfer from Co-B to Ru may result in the easier water dissociation step so as to facilitate the catalytic process. The resulting Ru@Co-B/Ni binder-free electrode could supply 10 mA cm−2 at overpotentials of 56 mV for HER and 280 mV for OER in 0.5 M phosphate buffer electrolyte. This work proposed a fruitful approach to advance the water splitting performance of transition metal boride in neutral media.

Synthesis and characterization of multinuclear ruthenium clusters assembled by terminal alkyne alcohols and ortho-carborane diselenolate ligands

Two novel half-sandwich trinuclear ruthenium complexes bridged by ortho-carborane-1,2-diselenolato ligands (p-cymene)Ru3(Se2C2B10H10)2(Se2C2B10H9)[HCCH(cyclo-C6H10)OCCH(cyclo-C6H10)] (2) and (p-cymene)Ru3(Se2C2B10H10)2(Se2C2B10H9)[HCCH(CH3)2COCCHC(CH3)2] (3) have been prepared by the reactions of ortho-carborane-1,2-diselenolate ligands and [(p-cymene)RuCl2]2 with CHC(cyclo-C6H10)(OH) and CHCC(OH)(CH3)2, respectively. The complexes have been fully characterized by 1H, 13C, and 11B NMR, mass and IR spectroscopy as well as by element analyzes. The molecular structures of two complexes have been determined by single-crystal X-ray diffraction analyzes.

Electrochemical atomic force microscopy of two-dimensional trinuclear ruthenium clusters molecular assembly and dynamics under redox state control.

Mixed-valence ruthenium trinuclear clusters containing dichloroacetates were synthesized, and the self-assembly of a single molecular adlayer composed of these clusters on a graphite surface was investigated by atomic force microscopy (AFM). AFM clearly revealed the dynamics of two-dimensional (2D) structure formation as well as the molecular characteristics of the adlayers at different electrochemical interfaces. The results verified that the design of metal complexes is important not only for redox chemistry but also for molecular assembly and nanoarchitecture construction.

Immobilization of a trimeric ruthenium cluster in mesoporous chromium terephthalate and its catalytic application.

Molecular trimeric ruthenium carboxylate clusters (Ru3 clusters) have been introduced into the pore channels of mesoporous metal-organic framework chromium terephthalate [MIL-101(Cr)] by employing a facile two-step post-synthetic strategy in which diamine hooks anchored on the framework metal nodes of the MOF are used to covalently immobilize the Ru3 clusters. The catalytic activity of the isolated Ru3 clusters in the pore channels of the MOF was significantly improved compared to the bulk counterpart.

Ru-Catalyzed Reverse Water Gas Shift Reaction with Near-Unity Selectivity and Superior Stability

Cascade catalysis of reverse water gas shift (RWGS) and well-established CO hydrogenation holds promise for the conversion of greenhouse gas CO2 and renewable H2 into liquid hydrocarbons and methanol under mild conditions. However, it remains a big challenge to develop low-temperature RWGS catalysts with high activity, selectivity, and stability. Here, we report the design of an efficient RWGS catalyst by encapsulating ruthenium clusters with the size of 1 nm inside hollow silica shells. The spatially confined structure prevents the sintering of Ru clusters while the permeable silica layer allows the diffusion of gaseous reactants and products. This catalyst with reduced particle sizes not only inherits the excellent activity of Ru in CO2 hydrogenation reactions but also exhibits nearly 100% CO selectivity and superior stability at 200–500 °C. The ability to selectively produce CO from CO2 at relatively low temperatures paves the way for the production of value-added fuels from CO2 and renewable H2.

Accelerating water reduction towards hydrogen generation via cluster size adjustment in Ru-incorporated carbon nitride

The metal cluster size and its interaction with the support has a strong impact on charge separation, water dissociation performance as well as durability of a heterogeneous catalyst. However, recent research on heterogeneous catalysis is predominantly devoted to enhancing the water splitting performance, but overlooks the fundamental concepts of relating cluster size as well as metal-support interaction with charge transfer ability and catalytic stability of electrocatalyst. Here, we report density functional theory along with experimental investigation that probe the relationship between particle size, intermediate structures, and energetics of water reduction on Rux (Ruthenium) clusters (x = 6, 13 and 55) on the g-CN support. The electrocatalytic activity for water reduction is found to dramatically oscillate as a function of the ‘Ru’ cluster size; the Ru55@CN catalyst shows the highest turnover rate 0.75 s−1 at 100 mV of H2 production. Density function theory (DFT) and experimental studies show a better stability and durability of Ru55@CN substrate due to its direct connection with five nitrogen atoms near the hole, along with one nitrogen at the hole center. In contrast, smaller clusters (Ru6 and Ru13) lead to greater distortion as they interact with only two neighboring nitrogen atoms in the pores of g-CN. The DFT study supported the Ru-N interaction in novel nitrogen-rich 2D g-CN structure which facilitates water dissociation and prohibits the undesired adsorption of active *OH groups. We hope optimization of metal’s cluster size and its interaction with the substrate might be an interesting approach for designing an electrocatalyst system.

Regulating the Coordination Environment of Ruthenium Cluster Catalysts for the Alkaline Hydrogen Evolution Reaction.

Exploring high-efficiency catalysts for the electrochemical hydrogen evolution reaction (HER) in alkaline environments is attractive but remains challenging. Here we report a coordination regulation strategy to tune the atomic structure of Ru cluster catalysts supported on Ti3C2Tx MXene (Ru-Ti3C2Tx) for the HER. We identify that the coordination number (CN) of Ru-Ru could be slightly regulated from 2.1 to 2.8 by adjusting the synthesized temperature so as to achieve an optimal catalytic configuration. The Ru-Ti3C2Tx with a CNRu-Ru of 2.8 exhibits the best catalytic activity with a low overpotential of 96 mV at 10 mA cm-2 and a mass activity about 11.5 times greater than the commercial Pt/C catalyst. Density functional theory calculations demonstrated that the small Ru clusters have a stronger covalent interaction with Ti3C2Tx support leading to an optimal ΔGH* value. This work opens up a general avenue to modulate the coordination environment of catalysts for the HER.

Preparation of trinuclear ruthenium clusters based on piconol ligands and their application in Oppenauer‐type oxidation of secondary alcohols

AbstractTreatment of Ru3(CO)12 with one equivalent of 2‐indolyl‐6‐pyridinyl‐alcohol ligands 2‐(C8H6N)‐6‐(CR1R2OH)C5H3N (R1 = R2 = Me (L1H); R1 = R2 = C2H5 (L2H); R1, R2 = −(CH2)4‐ (L3H);& R1, R2 = −(CH2)5‐ (L4H)) in refluxing THF afforded the corresponding trinuclear ruthenium clusters L(μ2‐H)Ru3(CO)9 (1a–1d), respectively. All the novel Ru complexes were well characterized by NMR, elemental analyses and IR spectra. Structures of complexes 1a, 1c, and 1d were further determined by X‐ray crystallographic studies. Complexes 1a–1d were applied to catalytic Oppenauer‐type oxidation of secondary alcohols with acetone as oxidant, and complex 1a was found to be the most efficient catalyst.

Tetranuclear ruthenium clusters anchored on polyoxometalates catalyze the hydrogenation of methyl levulinate in water

The tungstoaluminate-anchored ruthenium cluster catalyst is efficient and recyclable for the selective hydrogenation of methyl levulinate (ML) to gamma-valerolactone or methyl 4-hydroxypentanoate.

Liquid fuel synthesis via CO2 hydrogenation by coupling homogeneous and heterogeneous catalysis

Summary Synthesis of liquid fuel (C5+ hydrocarbons) via CO2 hydrogenation generally involves cascade catalysis of reverse water gas shift (RWGS) and Fischer-Tropsch synthesis (FTS) reactions over heterogeneous catalysts. Because of thermodynamic limitations of the cascade reactions, the reported heterogeneous catalysts usually suffer from high temperature (above 300°C) and low selectivity. Here, we report the liquid fuel production from CO2 hydrogenation by coupling homogeneous RuCl3 and heterogeneous Ru0 catalysts, which proceeded at the lowest temperature reported so far (180°C) and reached the highest C5+ selectivity to date (71.1%). The TOF of the CO2 hydrogenation reached 9.5 h−1, which is comparable with that of the reported Ru0 catalyzed FTS reaction using syngas. Detailed study indicates that synergy of homogeneous and heterogeneous catalysis is the key for the outstanding performance.

Effect on the Ligand of Triruthenium Unit for Hydrogen Evolution Reaction

At present, various energy problems occur on the earth. In order to solve the problems utilization of hydrogen is a candidate. Because hydrogen is a clean and highly efficient energy that does not produce sulfur oxides and nitrogen oxides and is attracting attention as a substitute for primary energy such as petroleum and natural gas. In this study, we focused on the ruthenium cluster unit (1-mer) forming a cyclic structure having three ruthenium ions in a mixed-valence state. Here, we examined a catalytic function of hydrogen evolution reaction (HER) at the 1-mer modified highly oriented pyrolytic graphite (HOPG) electrode. In addition, we have studied effects of alcohol as ligands for 1-mer. Cyclic voltammetry (CV) and linear sweep voltammetry (LSV) were used for electrochemical measurements. HOPG was modified by drop casting of 0.5 μM 1-mer dichloromethane or methanol solution and used as a working electrode. A Ag/AgCl (KCl sat.) or a reversible hydrogen electrode (RHE) was used as a reference electrode, and a platinum plate was used as a counter electrode. LSV and CV were carried out in 0.1 M HClO4 in the presence of various alcohols such as methanol and ethanol. Figure 1 shows the LSVs of 0.1 M HClO4 at the 1-mer modified HOPG. The surface concentration of 1-mer was cocurated to be 18 nmol cm-2. At the 1-mer modified HOPG electrode, the starting potential of HER was slightly shifted to positive as compared with that of bare HOPG electrode. This means that the 1-mer modified HOPG has a little catalytic activity for HER. On the other hand, addition of alcohol to the system changes drastically the catalytic activity of the HER. Onset potential of HER was shifted to positive by the addition of alcohol. Comparing the current densities in the presence of each alcohol at –0.80 V, the HER current was influenced by the kinds of alcohol. Especially, when methanol was added to the system, the current density of 0.02 A cm-2 at –0.80 V. Although the reason why the catalytic current for HER depends on the type of alcohol is not clear, it may be considered that the THF ligands of 1-mer are substituted by the alcohol used. We have been are studying the effect of surface concentration and nanoscale structure of 1-mer, and the anion of the electrolyte. Figure 1

Electrodeposition of Ruthenium-Doped Manganese Selenide for Energy-Related Materials

Selenium-based nanomaterials have attracted considerable attention for electrochemical hydrogen evolution and storage, fuel-cell catalysts, batteries, and electrochemical supercapacitors [1]. Among different selenium-based compounds, manganese selenide seems to be very interesting due to its magnetic and semiconducting properties. These properties are especially important in energy conversion and storage devices, electrochemical and gas sensors, and electrochromic devices [2]. The strong electrochemical properties of metal selenides can be improved by the introduction of ruthenium clusters [3].Many different methodologies have been used to obtain different Mn-Se nanostructures [2]; however, it seems that electrochemical techniques [1,4] are especially promising due to its simplicity, low-cost, and the possibility of controlling the composition, dimension, morphology, etc., of obtained materials. Unfortunately, there are limited literature reports devoted to the electrodeposition of those materials using a single bath solution.Therefore, this work is aimed at studying the influence of electrodeposition conditions (i.e., type of solvent, bath concentration, electrodeposition potential/current and duration, and hydrodynamic conditions in the electrolytic cell) on the morphology, chemical composition, structure, and electrochemical properties of manganese selenide and ruthenium-decorated manganese selenide.Manganese selenide and Ru-decorated manganese selenide have been electrodeposited onto the nickel foam using aqueous and non-aqueous (based on a mixture of choline chloride and ethylene glycol) baths containing (CH2COO)2Mn and SeO2 without or with the addition of RuCl3. Before electrodeposition, the reduction potentials were determined using linear sweep voltammetry (LSV) and differential pulse voltammetry (DPV). The morphology, chemical composition, and structure of as-obtained films were characterized using a field emission electron microscope (FE-SEM) coupled with an EDS analyzer system. X-ray powder diffraction (XRD) analysis was also performed. Acknowledgments This work was supported by the National Science Centre, Poland (Project no. 2017/26/M/ST5/00715).

Solid Acid Electrochemical Cell for the Production of Hydrogen from Ammonia

Summary Production of high-purity hydrogen by thermal-electrochemical decomposition of ammonia at an intermediate temperature of 250°C is demonstrated. The process is enabled by use of a solid-acid-based electrochemical cell (SAEC) in combination with a bilayered anode, comprising a thermal-cracking catalyst layer and a hydrogen electrooxidation catalyst layer. Cs-promoted Ru on carbon nanotubes (Ru/CNT) serves as the thermal decomposition catalyst, and Pt on carbon black mixed with CsH2PO4 is used to catalyze hydrogen electrooxidation. Cells were operated at 250°C with humidified dilute ammonia supplied to the anode and humidified hydrogen supplied to the counter electrode. A current density of 435 mA/cm2 was achieved at a potential of 0.4 V and ammonia flow rate of 30 sccm. With a demonstrated faradic efficiency for hydrogen production of 100%, the process yields hydrogen at a rate of 1.48 m o l H 2 / g c a t h .

Intrazeolite CO Methanation by Small Ruthenium Carbonyl Complexes: Translation from Free Clusters into the Cage

AbstractCatalytic CO methanation represents an important reaction to improve the feed gas quality for hydrogen fuel cells. Previously, the large potential of small bare and ligated ruthenium clusters as highly selective and active catalysts has been shown by employing gas phase clusters as model systems. Now, density functional theory (DFT) calculations are employed to demonstrate the possibility to translate the gas phase CO methanation reaction mediated by a ligated Ru4(CO)13H2+ complex into the framework of a ZSM‐5 zeolite. Such a translation, manifested by a reaction pathway which is mechanistically and energetically similar to the gas phase analogue, is possible since the zeolite framework does not influence the reactive center. Furthermore, we reveal the important role of the CO ligand environment in protecting the Ru4+ metal core from formation of bonds with the zeolite and in the creation of the reactive center by promoting the cooperatively enhanced adsorption and dissociation of H2.

Controllable synthesis for highly dispersed ruthenium clusters confined in nitrogen doped carbon for efficient hydrogen evolution

Modulating the size and dispersion of metal particles is highly desirable in nanocatalysis. Herein highly dispersed ruthenium clusters confined in nitrogen-doped carbon (RuNC) were synthesized by a one-pot pyrolysis of Ru(phen)3 organometallic compounds and glucose. The size of the Ru clusters was finely controlled at a cluster level (1.7 nm) to expose more catalytic active sites. The interaction between the Ru clusters and N species not only facilitated the uniform dispersion, but also prevented the aggregation of Ru clusters. This cluster-level RuNC manifested extraordinary catalytic performance towards the hydrogen evolution reaction (HER) and was comparable to or even better than a commercial Pt/C catalyst in basic and acidic media, respectively. Moreover, based on density functional theory (DFT) calculations, it was demonstrated that the N dopants in the carbon framework efficiently tailored the charge density distribution of the Ru centres and promoted the adsorption of H* on the catalyst, thus contributing to the high catalytic activity.