Ruthenium Catalysts Research Articles

XYLITOL PRODUCTION FROM XYLOSE OVER ZIRCONIA-DOPED SILICA SBA-15 SUPPORTED RUTHENIUM CATALYSTS

Xylitol is an important product of xylan valorization — the main hemicellulose of birch and aspen wood. Xylitol is obtained by direct hydrogenation of xylose. In present study, the xylose was obtained by acid hydrolysis of birch wood xylan. The industrial catalyst for the xylitol production process is Raney nickel. Pyrophoricity, tendency to sintering, Ni leaching and contamination of the product are actual problems of its use. We have developed new supported ruthenium catalysts based on mesoporous silicate SBA-15 doped with zirconia. The proposed method of modification of SBA-15 by doping with zirconia improves the hydrothermal stability. The deposited Ru is present in the form of highly dispersed RuO2 particles and is distributed evenly. The catalysts are stable, safe and environmentally friendly. Their high catalytic activity allows the process to be carried out in very mild conditions – in pure water at 70 °C and a pressure of 5.5 MPa H2. While the catalysts provide 96-99% selectivity for xylitol. The introduction of the developed catalysts into the xylitol production might reduce the product purification cost of and the process energy consumption, thereby improving ecological and economic indicators of deep chemical processing of plant raw materials.

Synthesis of Chiral 2‐Oxazolidinones by Ruthenium‐Catalyzed Asymmetric Transfer Hydrogenation of 2‐Oxazolones

AbstractAn asymmetric transfer hydrogenation of 2‐oxazolones in the presence of a chiral diamine ruthenium catalyst with potassium formate as a hydrogen source and potassium carbonate as an additive in 2,2,2‐trifluoroethanol is described. A series of chiral 2‐oxazolidinones were obtained with 29%–95% yields and 86%–>99% ee's. Furthermore, gram‐scale synthesis of chiral 2‐oxazolidinone and its downstream derivatizations demonstrate the practicality of this method.

Direct Synthesis of N-formamides by Integrating Reductive Amination of Ketones and Aldehydes with CO2 Fixation in a Metal-Organic Framework.

Formamides are important feedstocks for the manufacture of many fine chemicals. State-of-the-art synthesis of formamides relies on the use of an excess amount of reagents, giving copious waste and thus poor atom-economy. Here, we report the first example of direct synthesis of N-formamides by coupling two challenging reactions, namely reductive amination of carbonyl compounds, particularly biomass-derived aldehydes and ketones, and fixation of CO2 in the presence of H2 over a metal-organic framework supported ruthenium catalyst, Ru/MFM-300(Cr). Highly selective production of N-formamides has been observed for a wide range of carbonyl compounds. Synchrotron X-ray powder diffraction reveals the presence of strong host-guest binding interactions via hydrogen bonding and parallel-displaced π⋅⋅⋅π interactions between the catalyst and adsorbed substrates facilitating the activation of substrates and promoting selectivity to formamides. The use of multifunctional porous catalysts to integrate CO2 utilisation in the synthesis of formamide products will have a significant impact in the sustainable synthesis of feedstock chemicals.

Ruthenium catalysts based on porous aromatic frameworks synthesized by modified impregnation methods for hydrogenation of levulinic acid and its esters

Ruthenium catalysts supported on porous aromatic frameworks (PAFs) were synthesized using different protocols for metal impregnation to achieve high catalytic performance in the hydrogenation of levulinic acid. Significant effect of the support modification with functional groups (amino-, sulfo-) was demonstrated. The main factors affecting the process including substrate concentration, temperature, reaction time and hydrogen pressure were investigated. Ruthenium catalyst Ru-PAF-30-SO3H (COD) based on PAF-30 modified with sulfo groups synthesized with the use of 1,5-COD was able to promote levulinic acid dimerization at high temperatures (200–250 °C).

Hydrodeoxygenation of Lignin-Based Compounds over Ruthenium Catalysts Based on Sulfonated Porous Aromatic Frameworks.

Bifunctional catalysts are a major type of heterogeneous catalytic systems that have been widely investigated for biomass upgrading. In this work, Ru-catalysts based on sulfonated porous aromatic frameworks (PAFs) were used in the hydrodeoxygenation (HDO) of lignin-derived compounds: guaiacol, veratrole, and catechol. The relationship between the activity of metal nanoparticles and the content of acid sites in synthesized catalysts was studied. Herein, their synergy was demonstrated in the Ru-PAF-30-SO3H/5-COD catalyst. The results revealed that this catalytic system promoted partial hydrogenation of lignin-based compounds to ketones without any further transformations. The design of the Ru-PAF-30-SO3H/5-COD catalytic system opens a promising route to the selective conversion of lignin model compounds to cyclohexanone.

A Spectroscopic Approach on Permanganate Oxidation of 1-[(4-Chlorophenyl)methyl]piperidin-4-amine in Presence of Ruthenium(III) Catalyst with DFT Analysis on Reaction Mechanism Pathway

The kinetic oxidation of 1-[(4-chlorophenyl)methyl]piperidin-4-amine (CMP) using alkaline potassium permanganate in presence of Ru(III) as catalyst was conducted spectrophotometrically at 303 K. The Pseudo first-order reaction was maintained with regard to oxidant and substrate during the reaction at an ionic strength of 0.01 mol dm-3. The first-order kinetics has been depicted with respect to catalyst Ru(III) chloride and less than unit order with substrate and medium. For the slow step, different activation parameters including ΔH# (kJ mol-1), Ea (kJ mol-1), ΔG# (kJ mol-1) and ΔS# (J K-1 mol-1) were calculated. The effect of temperature, variation of substrate concentration, oxidant, ionic strength were studied. The stoichiometry ratio of the reaction to the substrate and oxidizing agent was found to be 1:4. The products of reaction were isolated and identified as chlorobenzene and L-alanine, N-(2-aminomethylethyl)-carboxylic acid by LC-MS spectra, a suitable mechanism has been proposed and the rate laws are derived. The frontier molecular orbital (FMO) and frontier electron density (FED) of piperidiamine and the oxidative products were studied using density functional theory (DFT). The results of the theoretical calculations supported the suggested reaction pathways.

Ammonia Synthesis and Decomposition in the Presence of Supported Ruthenium Catalysts

Ammonia Synthesis and Decomposition in the Presence of Supported Ruthenium Catalysts

Enhanced Fischer-Tropsch synthesis performance using graphene Nanosheets-Supported Cobalt-Ruthenium Nanocatalysts: Comparative study with γ-Alumina and carbon nanotubes supports

In this research, graphene Nanosheets (GNS) as Cobalt-Ruthenium Nanocatalysts support have been used in Fischer-Tropsch synthesis. The characterizations of catalysts were evaluated by Fourier-transform infrared spectroscopy (FTIR), Inductively Coupled Plasma (ICP), Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), Energy-dispersive X-ray spectroscopy (EDX), Temperature Programmed Reduction (TPR), and Transmission Electron Microscope (TEM). Afterward, the catalysts' activity, selectivity, and performance were assessed in a fixed-bed reactor at 25 bar. The results were compared by changing the catalyst base to γ-alumina (γ-Al2O3) and carbon nanotubes (CNTs). Measurements were performed in the temperature range of 320––340 °C, the gas ratio (H2/CO) of 2, and the gas hourly space velocity of 3 Lh-1gCat.-1. Using GNS as cobalt catalyst support in Fischer-Tropsch synthesis leads to the 64.5 % and 25.9 % increase in the percentage of CO conversion compared to γ-Al2O3 and CNTs, respectively. Additionally, the utilization of GNS support has resulted in an 11.1 % increase in heavy hydrocarbons selectivity of C5+, in comparison to γ-Al2O3, and a 9.5 % increase compared to CNTs. GNS-based synthesized catalyst with 10 wt% of cobalt and 0.1 wt% of ruthenium (catalyst #6) indicates the highest activity of catalyst at 320 °C with 72.3 % selectivity than heavy hydrocarbons C5+.

Atomically Dispersed Ruthenium Catalysts with Open Hollow Structure for Lithium–Oxygen Batteries

HighlightsThe open hollow structure enhances the accessibility of atomically dispersed Ru sites and improves the diffusion efficiency of catalytic moleculesThe abundant atomically dispersed Ru sites on the surface of catalyst provide a large number of oxygen adsorption and Li2O2 nucleation sitesThe lithium–oxygen battery assembled with h-RuNC could catalyze the production of Li2O2 with better dispersion and improve the cycling stability.

Ethanol as hydrogen donor: An efficient transfer hydrogenation of aldehydes, ketones, and nitroarenes with H-bonded Ru(II)-N-heterocyclic iminium complex

Isopropanol and formic acid are predominantly utilized as hydrogen sources in catalytic transfer hydrogenation reactions. However, the utilization of primary alcohols in such reactions has been sparsely documented, with only a limited number of reports available. In this article, we hereby present findings that underscore the prospective application of ecologically sustainable and economically viable ethanol, alongside a ruthenium(II) catalyst that exhibits remarkable resilience in the presence of moisture and oxygen. The air-stable Ru(II) complex (I) has been synthesized by non-covalently interacting anionic Ru(p-cymene)Cl3 and 1,3-diisopropyl-1H-perimidin-2(3H)-iminium (LH2+). The compound was subjected to experimental evaluation to conduct transfer hydrogenation reactions on aldehydes, ketones, and nitroarenes. The process entailed the utilization of ethanol, a hydrogen source that is both economically advantageous and ecologically benign. The hydrogen bond interaction existing between the Ru(p-cymene)Cl3 and LH2+ species plays a crucial in facilitating the exceptional catalytic efficiency exhibited by the Ru(II) complex (I). The reaction exhibits a wide range of substrate compatibility, enabling the hydrogenation of ketones, aldehydes, and nitroarenes. The results obtained from the control experiments have provided evidence for the formation of Ru − H species. A plausible mechanism has been hypothesized, relying on stoichiometric investigations.

Photo-mediated para-selective C(sp2)−H difluoroalkylations

Photo-mediated ruthenium-catalyzed para-C−H difluoroalkylation has been disclosed under extremely mild conditions. This photochemical ruthenium catalyst system is characterized by good functional group compatibility without additional photosensitizers at room temperature.

Asymmetric hydrogenation of isoquinolines with chiral cationic ruthenium diamine catalysts

A general asymmetric hydrogenation of isoquinolines catalyzed by chiral cationic ruthenium catalysts has been investigated. A wide range of isoquinoline derivatives, including 1-substituted, 3-substituted, 1,3-disubstituted and 3,4-disubstituted isoquinolines, were efficiently hydrogenated to give chiral tetrahydroisoquinolines with up to 92 % ee and >20:1 dr. It was found that the ruthenium catalyst bearing a non-coordinating BArF anion resulted in high enantioselectivity. Preliminary mechanistic studies revealed that the isoquinoline is reduced via a stepwise pathway, including 1,2-hydride addition, isomerization, and 2,3-hydride addition.

Porous Organic Polymer Supported Nano Ruthenium Catalysts for Cascade Aromatization of Quinoxalin-2(1H)-one and C-H Annulation with Alkynes.

Selective C-H annulation with alkynes is one of the most useful tools to synthesize heterocycles. Herein, we developed novel porous organic polymers supported ruthenium (POPs-Ru) as highly efficient catalysts for cascade aromatization of quinoxalin-2(1H)-one and C-H annulation with alkynes. Both terminal and internal alkynes were successfully transferred to furo[2,3-b]quinoxaline derivatives with good functional group tolerance and high regioselectivity by using POPs-Ru catalysts. Furthermore, the catalyst exhibited high activity and could be reused at least five times without obvious deactivation of this coupling reaction. This study offers an important platform for the immobilization of molecular metal catalysts for C-H functionalization.

Computational Investigation of Mononuclear Iron Water Oxidation Catalyst Design

Hydrogen production from non-carbon sources is an essential component of clean and sustainable technology for reducing greenhouse gas emissions from fuels. Water oxidation, which splits water molecules into hydrogen (protons) and molecular oxygen, is a thermodynamically challenging, multistep reaction achieved in photosynthetic organisms via photocatalysis by the Oxygen Evolving Complex (OEC) of Photosystem II. Mononuclear water oxidation catalysts that aim to mimic nature typically rely on heavy, rare metals such as ruthenium and iridium. Replacing these metals with iron is particularly appealing because it is abundant, benign, and inexpensive. We use density functional theory to characterize the catalytic ability of mononuclear iron photocatalysts compared with their ruthenium counterparts for 20 different ligand modifications with varying degrees of electron withdrawing behavior. We quantify the energetics, bond lengths, and charges in each of the steps leading to the highest oxidation state of the metal and necessary O-O bond formation in a mechanism determined experimentally for ruthenium catalysts and in many ways analogous to that followed by the OEC. Although many of the iron catalysts exhibited prohibitively high redox potentials in achieving the highest oxidation state required by this mechanism, a few display promising energetics and stability at each step explored. These results provide insights regarding the feasibility and performance of water oxidation catalysts using earth abundant metals as well as pinpointing mechanistic steps where catalytic ability degrades.

Barium Oxynitride Electride as Highly Enhanced Promotor for Ruthenium Catalyst in Ammonia Synthesis: Comparative Study with Barium Oxide

AbstractBarium oxide is a conventional promoter for various transition‐metal (TM) catalysts in ammonia synthesis. Ba‐promoted Ru catalysts are widely used for ammonia synthesis under mild reaction conditions. However, the promotion mechanism, including the active factor, remains unclear. In this study, the excellent promotion effect of barium oxynitride is reported, which creates anionic electrons in the lattice, forming an electride (BaOxNy:e−z) with the same rocksalt structure as BaO. The BaOxNy:e−z enhances the ammonia synthesis activity of the supported Ru catalyst by 40–100 fold compared with the BaO promotor. This study reveals that a low‐work‐function electron formed in the BaO lattice plays a pivotal role in the electronic promotion effect in catalytic ammonia synthesis, suggesting that BaOxNy:e−z formed near the surface during the ammonia synthesis reaction is an active species for the promotion effect of conventional BaO.

Self-Photosensitizing Dinuclear Ruthenium Catalyst for CO2 Reduction to CO.

The promise of artificial photosynthesis to solve environmental and energy issues such as global warming and the depletion of fossil fuels has inspired intensive research into photocatalytic systems for CO2 reduction to produce value-added chemicals such as CO and CH3OH. Among the photocatalytic systems for CO2 reduction, self-photosensitizing catalysts, bearing the functions of both photosensitization and catalysis, have attracted considerable attention recently, as such catalysts do not depend on the efficiency of electron transfer from the photosensitizer to the catalyst. Here, we have synthesized and characterized a dinuclear RuII complex bearing two molecules of a tripodal hexadentate ligand as chelating and linking ligands by X-ray crystallography to establish the structure explicitly and have used various spectroscopic and electrochemical methods to elucidate the photoredox characteristics. The dinuclear complex has been revealed to act as a self-photosensitizing catalyst, which acts not only as a photosensitizer but also as a catalyst for CO2 reduction. The dinuclear RuII complex is highly durable and performs efficient and selective CO2 reduction to produce CO with a turnover number of 2400 for 26 h. The quantum yield of the CO formation is also very high─19.7%─and the catalysis is efficient, even at a low concentration (∼1.5%) of CO2.

Plasma-Promoted Ammonia Decomposition over Supported Ruthenium Catalysts for COx -Free H2 Production.

The efficient decomposition of ammonia to produce COx -free hydrogen at low temperatures has been extensively investigated as a potential method for supplying hydrogen to mobile devices based on fuel cells. In this study, we employed dielectric barrier discharge (DBD) plasma, a non-thermal plasma, to enhance the catalytic ammonia decomposition over supported Ru catalysts (Ru/Y2 O3 , Ru/La2 O3 , Ru/CeO2 and Ru/SiO2 ). The plasma-catalytic reactivity of Ru/La2 O3 was found to be superior to that of the other three catalysts. It was observed that both the physicochemical properties of the catalyst (such as support acidity) and the plasma discharge behaviours exerted significant influence on plasma-catalytic reactivity. Combining plasma with a Ru catalyst significantly enhanced ammonia conversion at low temperatures, achieving near complete NH3 conversion over the 1.5 %-Ru/La2 O3 catalyst at temperatures as low as 380 °C. Under a weight gas hourly space velocity of 2400 mL gcat -1 h-1 and an AC supply power of 20 W, the H2 formation rate and energy efficiency achieved were 10.7 mol gRu -1 h-1 and 535 mol gRu -1 (kWh)-1 , respectively, using a 1.5 %-Ru/La2 O3 catalyst.

Redox transformations of Ru catalyst during NO oxidation at industrial nitric acid production conditions

Oxidation of nitric oxide is one of the main steps in the Ostwald process for industrial nitric acid production. This work summarises the use of γ-Al2O3 supported Ru catalyst to study the oxidation of NO to NO2 at ambient and 4 bar pressure with a feed of 10% NO, 6% O2, 15% H2O, and rest Ar. The catalyst was synthesised using wet impregnation and characterised by BET, CO chemisorption, H2-TPR, XPS, XRD, in-situ XAS-XRD and DRIFTS. We report the activity and kinetics of supported ruthenium catalyst for NO oxidation under realistic nitric acid plant conditions. The catalyst exhibited a promising low-temperature activity of 72% at 340 °C in complete nitric acid condition and 37% at 420 °C in partial nitric acid condition. An apparent activation energy of 152 kJ/mol was observed and the overall rate was determined to be r =kf.KG.PNO2.PO2PNO2, where kf and KG represents forward rate and equilibrium rate constants respectively. The reaction was found to be second order with respect to NO, first order with respect to O2 and inversely dependent on NO2 partial pressure. The stability of the catalyst was also tested during 45 h of isothermal NO oxidation at ambient pressure. From in-situ XAS-XRD and DRIFTS experiments it was revealed that during isothermal NO oxidation the reaction oscillates as the ruthenium surface goes through redox cycles. A plausible reaction mechanism that fits with our experimental observations and the oxidative nature of ruthenium is proposed. This study demonstrates and explains the capacity of supported ruthenium catalysts to oxidise NO to NO2 in industrial nitric acid production conditions.

Study of the catalytic wet air oxidation of p-hydroxybenzoic acid on a fresh ruthenium catalyst supported by different oxides

The catalytic wet air oxidation (CWAO) of p-hydroxybenzoic acid (p-HBA) was conducted in a batch reactor at 140 °C, and at a total air pressure of 50 bar over Ru-based catalysts. Four materials were selected as supports – TiO2, CeO2–TiO2, ZrO2–TiO2, and La2O3–TiO2 – all of which had mesopores in their texture and pollutant adsorption capacities. The supports were prepared by the sol-gel method, and then impregnated with 3 wt% of Ru precursor. Such characterization techniques as N2-sorption, XRD, XPS, H2–TPR, NH3-TPD, TEM, and HAADF-STEM were used to analyze the different solids. The correlation between catalytic activities and physicochemical properties was discussed. A significant specific surface area (SBET), a large amount of surface-active oxygen, and Lewis acidity sites were observed on cerium-containing catalysts (Ru/CeTi). Fresh Ru catalysts containing cerium showed higher activity than Ru/TiO2, Ru/ZrTi, and Ru/LaTi catalysts. It is assumed that the acidic sites and surface oxygen trap the p-HBA molecule, thus increasing the catalytic properties of the Ru particles which interact with the surface oxygen through the cerium redox process (Ce3+/Ce4+). As the presence of cerium increases surface-active oxygen, it inhibits the deposition of carbon on the surface of the Ru catalyst. The pseudo-second order (PSO) model adequately described the kinetic data of the p-HBA oxidation reaction using Ru catalysts.

Ru(II)-Catalyzed N-Methylation of Amines Using Methanol as the C1 Source.

Four ruthenium complexes were used as catalysts for the N-methylation of amines using methanol as the C1 source under weak base conditions. The (DPEPhos)RuCl2PPh3(1a) catalyst showed the best catalytic performance (0.5 mol %, 12 h). The deuterium labeling and control experiments suggested the reaction via the Ru-H mechanism. This study provides a new ruthenium catalyst system for N-methylation with methanol under weak base conditions.