Selective alcohol oxidation to aldehydes and ketones over base-promoted gold–palladium clusters as recyclable quasihomogeneous and heterogeneous metal catalysts

Bimetallic gold–palladium clusters, with an average size of 1.9 nm and composed of 80 mol% gold, proved to be highly active and selective metal catalysts for the organic phase oxidation with O₂ of aliphatic, allylic and benzylic alcohols to the corresponding carbonyl products. Polyvinylpyrrolidone stabilized gold–palladium clusters dispersed in N,N-dimethylformamide emerged as promising quasihomogeneous metal catalysts for the oxidation of benzyl alcohol to benzaldehyde with full selectivity; they could be efficiently recycled with unaffected catalytic performance by solvent-resistant nanofiltration. Highly active and durable heterogeneous catalysts for the amide phase or solvent-free alcohol oxidation were prepared by the quantitative immobilization of the optimized gold–palladium clusters on the high surface area basic BaAl₂O₄ spinel support with preservation of the bimetallic clusters’ nanodispersion.     

A Ru-Complex Tethered to a N-Rich Covalent Triazine Framework for Tandem Aerobic Oxidation-Knoevenagel Condensation Reactions

Herein, a highly N-rich covalent triazine framework (CTF) is applied as support for a Ru^III complex. The bipyridine sites within the CTF provide excellent anchoring points for the [Ru(acac)₂(CH₃CN)₂]PF₆ complex. The obtained robust Ru^III@bipy-CTF material was applied for the selective tandem aerobic oxidation-Knoevenagel condensation reaction. The presented system shows a high catalytic performance (>80% conversion of alcohols to α, β-unsaturated nitriles) without the use of expensive noble metals. The bipy-CTF not only acts as the catalyst support but also provides the active sites for both aerobic oxidation and Knoevenagel condensation reactions. This work highlights a new perspective for the development of highly efficient and robust heterogeneous catalysts applying CTFs for cascade catalysis.     

Physical and Chemical Properties and Activity of Fe–Co–Cu Oxide Catalysts in Oxidation of CO

We have studied the physical and chemical properties and activity of Fe–Co–Cu oxide catalysts in oxidation of CO. We have shown that the high activity of these catalysts is promoted by formation of the Cu₂(OH)₃NO₃ structure, which is modified by hematite clusters. The presence of OH groups is favorable for the formation of active sites for CO oxidation on the surface of the oxide catalysts.     

Highly Dispersed Ruthenium Hydroxide Supported on Titanium Oxide Effective for Liquid‐Phase Hydrogen‐Transfer Reactions

Supported ruthenium hydroxide catalysts (Ru(OH)_x/support) were prepared with three different TiO₂ supports (anatase TiO₂ (TiO₂(A), BET surface area: 316 m² g^?1), anatase TiO₂ (TiO₂(B), 73 m² g^?1), and rutile TiO₂ (TiO₂(C), 3.2 m² g^?1)), as well as an Al₂O₃ support (160 m² g^?1). Characterizations with X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), electron spin resonance (ESR), and X‐ray absorption fine structure (XAFS) showed the presence of monomeric ruthenium(III) hydroxide and polymeric ruthenium(III) hydroxide species. Judging from the coordination numbers of the nearest‐neighbor Ru atoms and the intensities of the ESR signals, the amount of monomeric hydroxide species increased in the order of Ru(OH)_x<Ru(OH)_x/TiO₂(C)<Ru(OH)_x/Al₂O₃<Ru(OH)_x/TiO₂(B)<Ru(OH)_x/TiO₂(A). These supported ruthenium hydroxide catalysts, especially Ru(OH)_x/TiO₂(A), showed high catalytic activities and selectivities for liquid‐phase hydrogen‐transfer reactions, such as racemization of chiral secondary alcohols and the reduction of carbonyl compounds and allylic alcohols. The catalytic activities of Ru(OH)_x/TiO₂(A) for these hydrogen‐transfer reactions were at least one order of magnitude higher than those of previously reported heterogeneous catalysts, such as Ru(OH)_x/Al₂O₃. These catalyses were truly heterogeneous, and the catalysts recovered after the reactions could be reused several times without loss of catalytic performance. The reaction rates monotonically increased with an increase in the amount of monomeric ruthenium hydroxide species, which suggests that the monomeric species are effective for these hydrogen‐transfer reactions.     

Cu?Ti?O catalyst for complex purification of gases

Cu–Ti–O catalysts activity in the reactions of complete oxidation of CO and C₄H₁₀, selective catalytic reduction of NO by ammonia, SO₂ oxidation to SO₃, as well as the catalyst resistance to sulfur poisoning were studied. We suggest these catalysts for the combined removal of NO, CO and toxic organics from flue gases.     

Surface Chemistry on Small Ruthenium Nanoparticles: Evidence for Site Selective Reactions and Influence of Ligands

The reactivity of two classes of ruthenium nanoparticles (Ru NPs) of small size, either sterically stabilized by a polymer (polyvinylpyrrolidone, PVP) or electronically stabilized by a ligand (bisdiphenylphosphinobutane, dppb) was tested towards standard reactions, namely CO oxidation, CO₂ reduction and styrene hydrogenation. The aim of the work was to identify the sites of reactivity on the nanoparticles and to study how the presence of ancillary ligands can influence the course of these catalytic reactions by using NMR and IR spectroscopies. It was found that CO oxidation proceeds at room temperature (RT) on Ru NPs but that the system deactivates rapidly in the absence of ligands because of the formation of RuO₂. In the presence of ligands, the reaction involves exclusively the bridging CO groups and no bulk oxidation is observed at RT under catalytic conditions. The reverse reaction, CO₂ reduction, is achieved at 120 °C in the presence of H₂ and leads to CO, which coordinates exclusively in a bridging mode, hence evidencing the competition between hydrides and CO for coordination on Ru NPs. The effect of ligands localized on the surface is also evidenced in catalytic reactions. Thus, styrene is slowly hydrogenated at RT by the two systems Ru/PVP and Ru/dppb, first into ethylbenzene and then into ethylcyclohexane. Selectively poisoning the nanoparticles with bridging CO groups leads to catalysts that are only able to reduce the vinyl group of styrene whereas a full poisoning with both terminal and bridging CO groups leads to inactive catalysts. These results are interpreted in terms of location of the ligands on the particles surface, and evidence site selectivity for both CO oxidation and arene hydrogenation.     

Catalytic Steam Reforming of Methane: New Data on the Contribution of Homogeneous Radical Reactions in the Gas Phase: II. A Ruthenium Catalyst

The kinetics of methane steam reforming and pyrolysis on Ru/Al₂O₃(T= 650–750°C, = 0.001–0.030 MPa) is studied. The values of the rates and activation energies are compared with the kinetic parameters for nickel catalysts. It was shown that steam reforming can occur on the ruthenium catalyst both heterogeneously and heterogeneously–homogeneously depending on the reaction conditions. Comparative activities of the Ru/Al₂O₃and Ni–Al₂O₃catalysts are discussed under the conditions of purely heterogeneous and heterogeneous–homogeneous steam reforming.     

Development of dipyridine‐based coordinative polymers for reusable heterogeneous catalysts

Poly(di(pyridin‐2‐yl)methyl acrylate) (PDPyMA), which was obtained by the free radical polymerization of designed coordinative monomer of di(pyridin‐2‐yl)methyl acrylate, is able to coordinate with various metal ions to form heterogeneous catalysts for diverse catalytic reactions. The Pd and Cu complexes supported by PDPyMA were developed for the heterogeneous Suzuki‐Miyaura reaction and Friedel‐Crafts alkylation, respectively. The PDPyMA‐based catalysts showed no significant decline of reactivity after five times recycling. However, the hydrolysis of the PDPyMA backbone under alkaline conditions limited the catalytic efficiency of this heterogeneous catalyst so that the coordinative monomer was redesigned as 1,1‐di(pyridine‐2‐yl)‐2‐(4‐vinylphenyl)ethan‐1‐ol and then 2,2′‐(1‐methoxy‐2‐(4‐vinylphenyl)ethane‐1,1‐diyl)dipyridine (MVPhDPy). With copolymerization of N‐isopropyl acrylamide (NIPAM), the efficiency of polymer‐based heterogeneous catalysts could be further raised, demonstrated by the increased turn over number in the Suzuki‐Miyaura reaction, which approached 5,260 by using the catalyst formed from poly(MVPhDPy‐co‐NIPAM) and Pd(OAc)₂. poly(MVPhDPy‐co‐NIPAM) copolymer, therefore, could be a versatile platform to support different metal ions for various heterogeneous catalytic reactions.     

Novel Nanoporous Binary Au?Ru Electrocatalysts for Glucose Oxidation

In this work, we study the fabrication, structural characterization, and electrochemical activity of titanium‐supported binary Au? Ru catalysts for glucose oxidation. The catalysts including Au₉₉Ru₁, Au₉₅Ru₅, Au₉₃Ru₇ and Au₈₈Ru₁₂ were prepared by a hydrothermal method using formaldehyde as a reduction agent. The morphologies of the prepared Au? Ru catalyst structures are characterized by porous dendritic particles with roughened surfaces with nano‐sized flakes. Electrochemical catalytic activity of the binary Au? Ru catalysts towards glucose oxidation in alkaline solutions was investigated using cyclic voltammetry and chronoamperometry. All binary Au? Ru catalysts facilitate glucose oxidation at the lower potentials and deliver higher anodic oxidation currents compared to pure Au catalyst. Among them, the binary Au₉₅Ru₅ catalyst presents the most negative onset potential of ?0.872 V (vs. Ag/AgCl, 3 M KCl) for glucose oxidation in 0.1 M NaOH solution. For the Au₉₅Ru₅ catalyst, chronoamperometric data at the potential step of ?0.65 V (vs. Ag/AgCl,3 M KCl) exhibit a well linear dependence of the anodic oxidation current density on glucose concentration in the range of 0 to 15 mM glucose.     

Selective CO Methanation over Ru Catalysts Supported on Nanostructured TiO2 with Different Crystalline Phases and Morphology

Nanostructured titanium dioxides were synthesized via various post-treatments of titanate nanofibers obtained from titanium precursors by hydrothermal reactions. The microstruc-tures of TiO₂ and supported Ru/TiO₂ catalysts were characterized with X-ray diffraction, transmission electron microscopy, energy-dispersive X-ray analysis, and nitrogen adsorption isotherms. The phase structure, particle size, morphology, and specific surface area were de-termined. The supported Ru catalysts were applied for the selective methanation of CO in a hydrogen-rich stream. The results indicated that the Ru catalyst supported on rutile and TiO₂-B exhibited higher catalytic performance than the counterpart supported on anatase, which suggested the distinct interaction between Ru nanoparticles and TiO₂ resulting from different crystalline phases and morphology.     

High‐Performance Ru1/CeO2 Single‐Atom Catalyst for CO Oxidation: A Computational Exploration

By means of density functional theory computations, we examine the stability and CO oxidation activity of single Ru on CeO₂(111), TiO₂(110) and Al₂O₃(001) surfaces. The heterogeneous system Ru₁/CeO₂ has very high stability, as indicated by the strong binding energies and high diffusion barriers of a single Ru atom on the ceria support, while the Ru atom is rather mobile on TiO₂(110) and Al₂O₃(001) surfaces and tends to form clusters, excluding these systems from having a high efficiency per Ru atom. The Ru₁/CeO₂ exhibits good catalytic activity for CO oxidation via the Langmuir–Hinshelwood mechanism, thus is a promising single‐atom catalyst.     

V2O5/TiO2 Catalyst Xerogels: Method of Preparation and Characterization

This work describes a modified sol-gel method for the preparation of V₂O₅/TiO₂ catalysts. The samples have been characterized by N₂ adsorption at 77 K, X-ray Diffractometry (XRD), Scanning Electronic Microscopy (SEM/EDX) and Fourier Transform Infrared Spectroscopy (FT-IR). The surface area increases with the vanadia loading from 24 m² g^–1 for pure TiO₂ to 87 m² g^–1 for 9 wt% of V₂O₅. The rutile form is predominant for pure TiO₂ but becomes enriched with anatase phase when vanadia loading is increased. No crystalline V₂O₅ phase was observed in the diffractograms of the catalysts. Analysis by SEM showed heterogeneous granulation of particles with high vanadium dispersion. Two species of surface vanadium were observed by FT-IR spectroscopy: a monomeric vanadyl and polymeric vanadates. The vanadyl/vanadate ratio remains practically constant. Ethanol oxidation was used as a catalytic test in a temperature range from 350 to 560 K. The catalytic activity starts around 380 K. For the sample with 9 wt% of vanadia, the conversion of ethanol into acetaldehyde as the main product was approximately 90% at 473 K.     

The determination of surface polarity of bismuth-molybdenum oxidation catalysts by gas chromatography

Summary The adsorption of aromatic and aliphatic hydrocarbons was investigated using gas chromatography on Bi₂O₃, MoO₃ and mixed Bi–Mo oxidation catalysts. As a measure of polarity of a catalyst, the difference between the chemical potential of aromatic and aliphatic hydrocarbons at the same surface concentration was used. The chemical potentials were estimated from elution chromatographic data. The data for C₆–C₉ methylbenzenes and C₆–C₁₂ n-alkanes were obtained in the temperature range 60–300°C in nitrogen as a carrier gas. Using air as carrier gas, introduction of water pulses on a catalyst does not change the elution characteristics. The elution of alkenes, alkynes, dienes and carbonyl compounds was disturbed by reaction of these compounds on the surface. The polarity of catalysts decreased in the order mixed Bi–Mo catalysts, MoO₃, Bi₂O₃. The polarities observed are compared with polarities of some other solids and liquids and the role of polarity of the surface in catalytic oxidation reactions is briefly discussed.     

Kinetics and reactivities of ruthenium(III)- and osmium(VIII)-catalyzed oxidation of ornidazole with chloramine-T in acid and alkaline media: A mechanistic approach

Ornidazole is an antiparasitic drug having a wide spectrum of activity. Literature survey has revealed that no attention has been paid towards the oxidation of ornidazole with any oxidant from the kinetic and mechanistic view point. Also no one has examined the role of platinum group metal ions as catalysts in the oxidation of this drug. Such studies are of much use in understanding the mechanistic profile of ornidazole in redox reactions and provide an insight into the interaction of metal ions with the substrate in biological systems. For these reasons, the Ru(III)- and Os(VIII)-catalyzed kinetics of oxidation of ornidazole with chloramine-T have been studied in HCl and NaOH media, respectively at 313 K. The oxidation products and kinetic patterns were found to be different in acid and alkaline media. Under comparable experimental conditions, in Ru(III)-catalyzed oxidation the rate law is −d[CAT]/dt = k [CAT]_o[ornidazole]_o^x[H⁺]^−y[Ru(III)]^z and it takes the form −d[CAT]/dt = k [CAT]_o[ornidazole]_o^x[OH⁻]^y[Os(VIII)][ArSO₂NH₂]^−z for Os(VIII)-catalyzed reaction, where x, y and z are less than unity. In acid medium, 1-chloro-3-(2-methyl-5-nitroimidazole-1-yl)propan-2-one and in alkaline medium, 1-hydroxy-3-(2-methyl-5-nitroimidazole-1-yl)propan-2-one were characterized as the oxidation products of ornidazole by GC–MS analysis. The reactions were studied at different temperatures and the overall activation parameters have been computed. The solvent isotope effect was studied using D₂O. Under identical set of experimental conditions, the kinetics of Ru(III) catalyzed oxidation of ornidazole by CAT in acid medium have been compared with uncatalyzed reactions. The relative rates revealed that the catalyzed reactions are about 5-fold faster whereas in Os(VIII) catalyzed reactions, it is around 9 times. The catalytic constant (K_C) has been calculated for both the catalysts at different temperatures and activation parameters with respect to each catalyst have been evaluated. The observed experimental results have been explained by plausible mechanisms. Related rate laws have been worked out.     

Catalytic activity of Ru/Fe2O3, obtained by adsorption of ruthenium on iron oxide supports

The effect of the method of a support preparation on its adsorption properties for ruthenium from solution and on the catalytic properties of Ru/Fe₂O₃ catalysts obtained by adsorption, has been studied. Moreover, the influence of the solvent in which a given ruthenium compound was dissolved on the properties of Ru/Fe₂O₃ catalysts was observed.     

High-temperature methane oxidation over metallic monolith-supported zeolite catalysts containing Mn,Co, and Pd ions

The high-temperature complete oxidation of methane over metallic monolith-supported zeolite catalysts containing isolated Mn, Co, and Pd ions was studied. The reaction involves heterogeneous and heterogeneous-homogeneous catalytic processes. The ratio between these processes depends on the temperature, feed rate, and the amount of catalyst charged in the reactor. In the heterogeneous catalytic process, the activity of the catalysts supported on the Fe—Cr—Al monolithic alloy decreases in the series Pd > Mn > Co > Fe—Cr—Al monolith and the reaction rate uniformly increases with increasing contact time. In the heterogeneous-homogeneous process, the reaction rate drastically increases and a 100% conversion of methane to CO₂ can be achieved by minor variations of the contact time. In this case, methane oxidation depends not only on the catalyst chemical composition but also on its external surface area and the reaction volume.     

A Dinuclear Ruthenium‐Based Water Oxidation Catalyst: Use of Non‐Innocent Ligand Frameworks for Promoting Multi‐Electron Reactions

Insight into how H₂O is oxidized to O₂ is envisioned to facilitate the rational design of artificial water oxidation catalysts, which is a vital component in solar‐to‐fuel conversion schemes. Herein, we report on the mechanistic features associated with a dinuclear Ru‐based water oxidation catalyst. The catalytic action of the designed Ru complex was studied by the combined use of high‐resolution mass spectrometry, electrochemistry, and quantum chemical calculations. Based on the obtained results, it is suggested that the designed ligand scaffold in Ru complex 1 has a non‐innocent behavior, in which metal–ligand cooperation is an important part during the four‐electron oxidation of H₂O. This feature is vital for the observed catalytic efficiency and highlights that the preparation of catalysts housing non‐innocent molecular frameworks could be a general strategy for accessing efficient catalysts for activation of H₂O.     

Influence of selenium on the catalytic properties of ruthenium-based cluster catalysts for oxygen reduction

The favourable influence of selenium on the catalytic properties of Ru-based catalysts for the oxygen reduction reaction in acid electrolytes has been investigated by rotating disk electrode measurements. Compared to the oxygen reduction of selenium-free Ru-based catalysts, the overpotential at low current densities (ca. 10 μA cm⁻²) is not affected by the presence of selenium whereas selenium-containing catalysts show higher current densities under fuel cell relevant conditions. The kinetically controlled current density at 0.6 V versus SHE increases 4–5 fold with increasing selenium content. A maximum value is obtained at about 15 mol% Se. This effect is tentatively explained by a modification of the catalytic active centre, which is assumed to consist of Ru---C---CO complexes. IR spectroscopic investigations indicate a reaction of selenium with these complexes. This model is also supported by the study of the electrooxidation of CO. In contrast to the selenium-free catalyst, no CO oxidation is observed on the selenium-containing catalyst. Additional effects of selenium are an enhanced stability towards electrochemical oxidation and a lower amount of Ru oxides formed during synthesis, as evidenced from XRD investigations. Direct four electron oxygen reduction to water is efficient and H₂O₂ production of these catalysts is small (about 5% at potentials <0.3 V vs. SHE ).     

Synthesis of Supported Bimetal Catalysts using Galvanic Deposition Method

Supported bimetallic catalysts have been studied because of their enhanced catalytic properties due to metal‐metal interactions compared with monometallic catalysts. We focused on galvanic deposition (GD) as a bimetallization method, which achieves well‐defined metal‐metal interfaces by exchanging heterogeneous metals with different ionisation tendencies. We have developed Ni@Ag/SiO₂ catalysts for CO oxidation, Co@Ru/Al₂O₃ catalysts for automotive three‐way reactions and Pd−Co/Al₂O₃ catalysts for methane combustion by using the GD method. In all cases, the catalysts prepared by the GD method showed higher catalytic activity than the corresponding monometallic and bimetallic catalysts prepared by the conventional co‐impregnation method. The GD method provides contact between noble and base metals to improve the electronic state, surface structure and reducibility of noble metals.     

Ruthenium and enzyme-catalyzed dynamic kinetic resolution of alcohols

Ruthenium acts as a good catalyst for the racemization reaction of secondary alcohols and amines. Ruthenium-catalyzed racemization is coupled with enzymatic kinetic resolution to prepare chiral compounds in 100% theoretical yield. Ten ruthenium complexes (1–10) act as a good catalyst the for racemization reaction and are also compatible with DKR process. Two other ruthenium complexes [RuCl₂(PPh₃)₃] and [Cp^*RuCl(COD)] are active for racemization reaction but their successful compatibility with DKR has not yet been reported. Ru/γ-Al₂O₃ and Ru–HAP are the heterogeneous catalysts used for the racemization reaction. They have also not been employed for DKR process. Polymer supported ruthenium is employed as a reusable racemization catalyst for aerobic DKR of alcohols.