Catalytic Ru Research Articles

Bioinspired Water Preorganization in Confined Space for Efficient Water Oxidation Catalysis in Metallosupramolecular Ruthenium Architectures.

ConspectusNature has established a sustainable way to maintain aerobic life on earth by inventing one of the most sophisticated biological processes, namely, natural photosynthesis, which delivers us with organic matter and molecular oxygen derived from the two abundant resources sunlight and water. The thermodynamically demanding photosynthetic water splitting is catalyzed by the oxygen-evolving complex in photosystem II (OEC-PSII), which comprises a distorted tetramanganese-calcium cluster (CaMn4O5) as catalytic core. As an ubiquitous concept for fine-tuning and regulating the reactivity of the active site of metalloenzymes, the surrounding protein domain creates a sophisticated environment that promotes substrate preorganization through secondary, noncovalent interactions such as hydrogen bonding or electrostatic interactions. Based on the high-resolution X-ray structure of PSII, several water channels were identified near the active site, which are filled with extensive hydrogen-bonding networks of preorganized water molecules, connecting the OEC with the protein surface. As an integral part of the outer coordination sphere of natural metalloenzymes, these channels control the substrate and product delivery, carefully regulate the proton flow by promoting pivotal proton-coupled electron transfer processes, and simultaneously stabilize short-lived oxidized intermediates, thus highlighting the importance of an ordered water network for the remarkable efficiency of the natural OEC.Transferring this concept from nature to the engineering of artificial metal catalysts for fuel production has fostered the fascinating field of metallosupramolecular chemistry by generating defined cavities that conceptually mimic enzymatic pockets. However, the application of supramolecular approaches to generate artificial water oxidation catalysts remained scarce prior to our initial reports, since such molecular design strategies for efficient activation of substrate water molecules in confined nanoenvironments were lacking. In this Account, we describe our research efforts on combining the state-of-the art Ru(bda) catalytic framework with structurally programmed ditopic ligands to guide the water oxidation process in defined metallosupramolecular assemblies in spatial proximity. We will elucidate the governing factors that control the quality of hydrogen-bonding water networks in multinuclear cavities of varying sizes and geometries to obtain high-performance, state-of-the-art water oxidation catalysts. Pushing the boundaries of artificial catalyst design, embedding a single catalytic Ru center into a well-defined molecular pocket enabled sophisticated water preorganization in front of the active site through an encoded basic recognition site, resulting in high catalytic rates comparable to those of the natural counterpart OEC-PSII.To fully explore their potential for solar fuel devices, the suitability of our metallosupramolecular assemblies was demonstrated under (electro)chemical and photocatalytic water oxidation conditions. In addition, testing the limits of structural diversity allowed the fabrication of self-assembled linear coordination oligomers as novel photocatalytic materials and long-range ordered covalent organic framework (COF) materials as recyclable and long-term stable solid-state materials for future applications.

Sol–Gel Synthesized Nickel‐Doped Ruthenium Oxide Aerogel for Highly Efficient Acidic Hydrogen Evolution Reaction

Solar and wind energy for water electrolysis are gaining interest in contemporary times. In this context, platinum catalysts are commonly recognized as the standard for the hydrogen evolution reaction (HER), yet their effectiveness is constrained by their high cost and inadequate stability. Combining Ru and Ni lowers the material expense and greatly improves the electrocatalytic performance. Therefore, in the present study, a 3D nanostructured amorphous RuO2 aerogel is doped with various concentrations of Ni for enhanced HER activity. The results indicate that the 4% Ni‐RuO2 aerogel exhibits a 0D colloidal network featuring interconnected mesopores, with a high specific surface area of 241.5 m2·g−1. In addition, the 4% Ni‐RuO2 aerogel catalyst exhibits the lowest overpotentials of 63 and 122 mV at current densities of 10 and 50 mA·cm−2, respectively, along with enhanced hydrogen adsorption activity for the HER due to the 3D porous structure of the aerogel. However, a further increase in Ni doping leads to a decrease in HER activity due to a reduction in the number of catalytic Ru sites. The study found that doping with the optimum amount of Ni causes a redistribution of charges on the sample surface, thereby uncovering more reaction sites and enhancing the electrocatalytic performance.

Extended aging of Ru-Ni, Na2O/Al2O3 dual function materials (DFM) for combined capture and subsequent catalytic methanation of CO2 from power plant flue gas

This study investigates the use of catalytic Ru and Ni combinations, intimately mixed with Na2O supported on γ-Al2O3 DFMs (dual function materials). We refer to these as dual function since one material – composed of an alkaline sorbent and catalytic component intimately dispersed on a high surface area carrier – can be used to capture CO2 from power plant flue gas and subsequently upgrade it to methane. The goal is to reduce the Ru content by combining it with catalytic Ni. Due to the presence of O2 in flue gas, Ni-only DFMs are not suitable candidates as they are oxidized and cannot be reactivated at temperatures below 550 °C. However, with the addition of small amounts of Ru, NiO can be reduced at DFM operating temperatures (∼300 °C, consistent with the exhaust temperature of natural gas flue gas), increasing catalytic sites for methanation. Several Ru + Ni combinations are investigated (0.5 % Ru, x% Ni, 6.1 % “Na2O”/Al2O3, x = 1, 5, 10, 20) for cyclic capture/methanation performance to identify an optimal formulation. 0.5 % Ru, 5 % Ni, 6.1 % “Na2O”/Al2O3 DFM is then aged in simulated, O2– and steam-containing natural gas flue gas. Aging over 60 cycles shows that there is steady deactivation in performance with XRD and STEM/EDS showing that the formation of inactive and stable NiAl2O4 is the primary cause for decreased methanation ability.

Insights into the cyclic CO2 capture and catalytic methanation over highly performing Li-Ru/Al2O3 dual function materials

The combined CO2 capture and in-situ methanation using renewable hydrogen over dual function sorbent-catalyst materials is a chemical looping process with strong potential to increase the efficiency and reduce the cost of current CCU technologies. In this work, we set out to develop highly performing Lithium-Ruthenium/Al2O3 investigating synergic and mechanistic aspects involved in the alternate CO2 adsorption and hydrogenation phases. Catalysts with low Ru loading (max 1% wt.) and fixed dispersion on Al2O3 spheres were promoted with variable amounts of Li (1–5% wt.) and characterized by BET, PSD, XRD, H2 chemisorption, CO2-TPD, TG-MS, H2-TPSRx and CO2 catalytic methanation under continuous flow conditions. Transient CO2 storage/methanation cycles were studied in a fixed bed reactor that was operated at several temperature levels (250–350 °C) with alternate feed conditions of variable duration. The cycled CO2 adsorption and methanation were also investigated by in-situ DRIFT comparing results for xLi-Ru/Al2O3 materials against the reference Ru/Al2O3 catalyst. The favourable synergism existing at the nanoscale between the Li-aluminate sorbent phase and the catalytic Ru sites enhances the intrinsic activity of the DFMs that can guarantee high methane productivity and selectivity with low noble metal loadings.

Double-ligand Fe, Ru catalysts: A novel route for enhanced H2 production from Formic Acid

Catalytic Ru- or Fe-complexes bearing two ligands L1, L2, where L1 = phosphine and L2 = Schiff-base ligand, present remarkable H2 production efficiency from Formic Acid (FA) than their single-ligand counterparts. The optimum L1RuL2 and L1FeL2 catalysts were obtained using a phosphine = P(CH2CH2PPh2)3 (or PP3) as L1 and a Schiff-base ligand (abbreviated Lγ herein) as L2, while the using of amino functionalized nanoparticle H2N@SiO2 as cocatalyst further promotes the H2 production efficiency. In long term stability experiments [RuPP3Lγ]/H2N@SiO2 and [FePP3Lγ]/H2N@SiO2 achieve a total TONs >17,367 and >29,372 respectively without deactivation. Thermodynamic and spectroscopic data reveal a common catalytic mechanism for both Fe and Ru based systems, involving synergism between L1, L2 in order to promote the rate-limiting steps. The present work is the first example of “double-ligand catalyst” concept as a novel route for high-efficiency, HCOOH dehydrogenation catalysts, which can be operative for either noble-metal or earth-abundant metals.

Synthesis of 4,4-Difluoroalkenes by Coupling of α-Substituted α,α-Difluoromethyl Halides with Allyl Sulfones under Photoredox Catalyzed Conditions.

Photoredox-catalyzed allylation of α-gem-difluorinated organohalides with allyl sulfones proceeded smoothly under visible light irradiation to give 4,4-difluoroalkenes in good yields. In the presence of catalytic Ru(bpy)3Cl2, Hantzsch ester, and diisopropylethylamine, the reaction was complete within 2 h. Using the same methodology, three-component cascade reactions to give 6,6-difluoroalkenes were carried out successfully.

Direct Synthesis of Methyl Formate from CO2 With Phosphine-Based Polymer-Bound Ru Catalysts.

Methyl formate was produced in one pot through the hydrogenation of CO2 to formic acid/formate followed by an esterification step. The route offers the possibility to integrate renewable energy into the fossil-based chemical value chain. In this work, a phosphine-polymer-anchored Ru complex was shown to be an efficient solid catalyst for the direct hydrogenation of CO2 to methyl formate. The 1,2-bis(diphenylphosphino)ethane-like polymer presented the highest activity with a turnover number (TON) of up to 3401 at 160 °C. The reaction parameters were systemically investigated to optimize the reaction towards the formation of methyl formate. This catalyst could be reused seven times without a significant decrease in activity. Evolution of the catalytic Ru center during the reaction was revealed, and a possible reaction mechanism was proposed.

Catalytic Ru containing Pt3Mn nanocrystals enclosed with high-indexed facets: Surface alloyed Ru makes Pt more active than Ru particles for ethylene glycol oxidation

Tuning the surface property of Pt based nanocrystals at the atomic level is of vital significance to meet superior electrocatalytic performance criteria. In this work, a new strategy to advance fundamental surface study on Pt based nanocrystals is addressed by implanting foreign metals as “active auxiliaries” onto the surface of Pt based nanocrystals to engineer a stable structured catalyst. Under the guidance of this concept, the Ru component was selected as “active auxiliary” to construct Ru containing Pt3Mn catalysts by doping the isolated Ru atoms (Pt3Mn–Ru) and Ru nanoparticles (Pt3Mn@Ru) onto surface layer of Pt3Mn concave nanocubes (CNCs). Strikingly, the Pt3Mn–Ru CNCs showed the most optimal catalytic activity, durability and CO anti-poisoning ability toward ethylene glycol oxidation reaction (EGOR). The specific activity of Pt3Mn–Ru CNCs is 1.32 mA cm−2, which is 1.47 and 3.07 times higher than Pt3Mn@Ru CNCs (0.90 mA cm−2) and pure Pt3Mn CNCs (0.43 mA cm−2). The results of in situ Fourier transform infrared spectroscopy experiments revealed that Pt3Mn–Ru CNCs were more in favor of CC bond cleavage of EG and rapid oxidation/removal of intermediate poisonous COads. Furthermore, the theoretical calculations revealed that the Pt3Mn–Ru CNCs possessed a lower reaction barrier (1.69 eV) for oxidation of COads assisted by adsorbed OHads species, and an energy-favorable position (2.88 Å) for reaction between COads and OHads. This work disclosed a new tactics to develop a novel structured catalyst in possession of excellent electrocatalytic performance, which provided a promising methodology for designing Pt-based nanoparticles as efficient fuel cell catalysts.

Development of catalytic membranes over PdAu selective films for hydrogen production through the dry reforming of methane

PdAu composite membranes were applied in the preparation of catalytic membranes for hydrogen production. The APTES surface modification of PdAu membranes synthesized by sequential electroless deposition was carried out. Grafted samples were analyzed by means of XPS, SEM-EDS and DRIFT. XPS data showed that surface saturation was reached when a 0.5 v/v % of APTES was employed. The morphological study of the samples showed that after APTES functionalization a slightly change on the PdAu microstructure occurred. It was observed that the APTES-functionalized samples were stable after heating to 823 K for 2 h. In addition, these membranes retained their hydrogen permeability without detrimental effect over their selectivity. Catalytic Ru and Rh-based membranes were synthesized by the dip-coating method. The membranes were evaluated in the dry reforming of methane at 823 K. Even though only low conversions were obtained, these were slightly higher than those obtained for a fixed-bed reactor with the same amount of catalyst.

Reverse water gas shift reaction using supported ionic liquid phase catalysts

The reverse water–gas shift reaction (RWGSR) using a supported ionic liquid-phase (SILP) catalyst consisting of Ru catalyst, ionic liquid (1-butyl-3-methylimidazolium chloride ([C4mim]Cl)), and porous silica gel support, was investigated. The catalytic activity of the SILP catalyst toward RWGSR strongly depends on the kind of Ru catalyst and amount of IL. Among the three kinds of Ru catalysts ([RuCl2(CO)3]2, Ru3(CO)12, and RuCl3), [RuCl2(CO)3]2 exhibits the best catalytic activity. Brunauer–Emmett–Teller (BET) surface area analysis and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analyses of the SILP catalyst based on [RuCl2(CO)3]2 and [C4mim]Cl revealed that both the solvation of the active catalytic Ru species and the surface area of the ionic liquid phase strongly affect catalytic activity. Hence, these factors help to determine the optimum amount of [C4mim]Cl in the SILP catalyst. The resulting SILP catalyst, with an optimum constitution, exhibited greater catalytic activity than the homogeneous system in which the same amounts of [RuCl2(CO)3]2 and [C4mim]Cl were employed. Catalytically active Ru species during RWGSR in both systems were investigated by means of electrospray ionization-mass spectrometry (ESI-MS). Interestingly, the rate-determining step in the two systems was different, implying that the silica support lowers the activation energy of the protonation reaction in the catalytic cycle. Therefore, the facilitation of the RWGSR by a SILP catalyst system can be realized by good mass transport, derived from the large surface area, as well as the effect of the silica support on activation energy. Furthermore, 20 cycles of the RWGSR using the SILP catalyst were accomplished.

A novel Ru–polyethersulfone (PES) catalytic membrane for highly efficient and selective hydrogenation of furfural to furfuryl alcohol

A novel catalytic Ru–PES membrane has been synthesised, characterised and evaluated for the selective hydrogenation of furfural to furfuryl alcohol. The Ru–PES membrane exhibited an high catalytic activity towards furfuryl alcohol (selectivity >99%) with turnover frequency (TOF) as high as 48 000 h−1.

Supported Ru Metalloporphyrins for Electrocatalytic CO2 Conversion

AbstractThis paper reports for the first time a computational analysis of the redox properties of graphene‐supported Ru‐porphyrins as potential catalytic materials for electrochemical CO2 reduction. Density functional theory reveals that such catalytic ensembles can efficiently activate both CO2 and CH4 molecules indicating their generic utility as C1‐functionalization catalysts. The charge transfer from the graphene surface to the catalytic Ru centers influences the thermodynamic stability of the key reaction intermediates and therefore determines the selectivity of the electrochemical process. The electrochemical reduction of CO2 can yield CO or methane, depending on the applied potential and reaction conditions. Calculations also identified alternative paths towards methanol and formic acid.

Studies on Thermal Atomic Layer Deposition of Silver Thin Films

The growth of Ag thin films by thermal atomic layer deposition (ALD) was studied. A commercial Ag compound, Ag(fod) (PEt3), was applied with a reducing agent, dimethyl amineborane (BH3(NHMe2)). A growth rate of 0.3 A/cycle was measured for Ag at a deposition temperature of 110 °C. The purity of the particulate, polycrystalline Ag thin films was studied with time-of-flight elastic recoil detection analysis (TOF-ERDA) and X-ray photoelectron spectroscopy (XPS). TOF-ERDA showed only small amounts of impurities in the film deposited at 110 °C, the main impurities being oxygen (1.6 at. %), hydrogen (0.8 at. %) and carbon (0.7 at. %). In addition to the conventional ALD process, the idea of activation of the amineborate inside the ALD reactor was tested. A catalytic Ru surface was utilized to convert BH3(NHMe2) into possibly even more reducing species inside the reactor without contaminating the catalysts with a growing film.

Photocatalytic Activity of Carbon Nitride Modified with a Ruthenium(II) Complex Having Carboxylic- or Phosphonic Acid Anchoring Groups for Visible-light CO2 Reduction

Semiconducting C3N4 powder modified with a catalytic Ru(II) complex having carboxylic acid groups as anchors showed higher activity for CO2 reduction into HCOOH under visible light (λ > 400 nm) at ...

Resolving Surface Structures of Catalytic Ru Nanoparticles during Catalysis

Resolving Surface Structures of Catalytic Ru Nanoparticles during Catalysis

Fragment Coupling and the Construction of Quaternary Carbons Using Tertiary Radicals Generated From tert-Alkyl N-Phthalimidoyl Oxalates By Visible-Light Photocatalysis.

The coupling of tertiary carbon radicals with alkene acceptors is an underdeveloped strategy for uniting complex carbon fragments and forming new quaternary carbons. The scope and limitations of a new approach for generating nucleophilic tertiary radicals from tertiary alcohols and utilizing these intermediates in fragment coupling reactions is described. In this method, the tertiary alcohol is first acylated to give the tert-alkyl N-phthalimidoyl oxalate, which in the presence of visible-light, catalytic Ru(bpy)3(PF6)2, and a reductant fragments to form the corresponding tertiary carbon radical. In addition to reductive coupling with alkenes, substitution reactions of tertiary radicals with allylic and vinylic halides is described. A mechanism for the generation of tertiary carbon radicals from tert-alkyl N-phthalimidoyl oxalates is proposed that is based on earlier pioneering investigations of Okada and Barton. Deuterium labeling and competition experiments reveal that the reductive radical coupling of tert-alkyl N-phthalimidoyl oxalates with electron-deficient alkenes is terminated by hydrogen-atom transfer.

Fe(6-Me-PyTACN)-catalyzed, one-pot oxidative cleavage of methyl oleate and oleic acid into carboxylic acids with H2O2 and NaIO4

The first Fe-based catalytic system for the oxidative cleavage of unsaturated fatty acids and esters to carboxylic acids is reported. The system comprises [Fe(OTf)2(6-Me-PyTACN)] (2) (6-Me-PyTACN = 1-[(6-methyl-2-pyridyl)methyl]-4,7-dimethyl-1,4,7-triazacyclononane, OTf = trifluoromethane sulfonate anion) as the catalyst (3 mol%) either with a combination of hydrogen peroxide and NaIO4 or exclusively with NaIO4 as the oxidant, and operates at 0 °C or ambient temperature. Under these standard conditions (method A), methyl oleate is converted in a one-pot procedure into 50–55% of both nonanoic and azelaic acid, together with some epoxide and aldehyde intermediates as byproducts. These yields can be further improved by addition of sulfuric acid (method B) to hydrolyze the epoxide byproducts, by including a pH neutralization step and addition of more catalyst (1 mol%). Under the optimized conditions, both methyl oleate and oleic acid are converted into high yields of the corresponding carboxylic acids (80–85%). Overall, this catalytic system provides an alternative to the industrial ozonolysis of oleic acid and to catalytic Ru- and Os-based systems for the oxidative cleavage of unsaturated fatty acids and esters.

Support‐Induced Oxidation State of Catalytic Ru Nanoparticles on Carbon Nanofibers that were Doped with Heteroatoms (O, N) for the Decomposition of NH3

AbstractRu nanoparticles were supported on monoliths that were coated with variously functionalized carbon nanofibers (CNFs), that is, un‐doped CNFs, CNFs that had been post‐treated with H2O2, and CNFs that had been doped with nitrogen during their growth. The Ru uptake (by equilibrium adsorption) onto N‐doped CNFs was larger compared to that on their un‐doped and O‐doped counterparts. The functionalization of the CNF support did not play a significant role in determining the size of the deposited Ru nanoparticles, but it substantially impacted on the sintering under the reaction conditions and on the electron density of the reduced metal. Among the catalysts on the different CNF supports, Ru on N‐CNF exhibited the highest H2 productivity from ammonia decomposition, which pointed to electronic effects that were induced by functionalization of the support.

Visible light photooxidative cyclization of amino alcohols to 1,3-oxazines

1,3-Amino alcohols were prepared to examine how structure affects the oxidation of tertiary amines in visible light photocatalysis. These substrates were cyclized to produce oxazines following the photooxidative formation of iminium ions using catalytic Ru(bpy)3Cl2. Amino alcohol derivatives of tetrahydroisoquinoline, tetrahydroquinoline, pyrrolidine, and Δ3-piperidine all were found to be viable substrates. In the case of the unsaturated piperidines, cyclization is accompanied by addition of methanol across the alkene; most likely occurring via a conjugate addition to an intermediate α,β-unsaturated iminium ion prior to oxazine formation.

Bifunctional FePt@MWCNTs/Ru Nanoarchitectures: Synthesis and Characterization

The synthesis of novel nanoarchitectures is an important way to combine several properties into the same nanometric object. Magnetic, catalytic, optical, and electrical properties can be embedded and used for heating, moving, or monitoring the nanocomposite. Following this approach, smart materials exhibiting remarkable properties could be obtained. Several nanocomposites are based on carbon nanotubes (CNTs). Because of the presence of empty cavities and very large surface external area, this allotropic form of carbon is especially suitable for this purpose and particularly for catalytic applications. In this work, a new general strategy to synthesize by a wet method three-block, smart nanocomposites based on MWCNTs is described. The new bifunctional material is shortly referred to as FePt@MWCNTs/Ru(NPs) to point out that nanoparticles (NPs) of a magnetically soft alloy (FePt fcc) fill the MWCNTs cavity, whereas catalytic Ru NPs decorate the external wall. In this way well separated catalytic and magnetic...