Relative Catalytic Activity Research Articles

Facile construction of binary metal oxide heterojunction with hexagonal boron nitride nanohybrid electrocatalyst for the detection of flutamide

BackgroundFlutamide (FU) is a potential anti-androgen drug significantly prescribed to all human beings. The high solubility and poor degradability of its metabolites can adversely affect the balance of the ecosystem. Therefore, developing an efficient and reliable technique to detect this pollutant is essential. Consequently, electrochemical sensors have been widely used for the monitoring of various real-world samples. MethodsHence, nickel-zinc oxide (NZO) with hexagonal boron nitride (h-BN) nanocomposite was prepared as a proficient electrocatalyst in FU detection. Several spectroscopic measurements were carried out to characterize the prepared materials. Our NZO/h-BN nanocomposite was utilized to modify the glassy carbon electrode (GCE) and its relative catalytic activity was scrutinized with impedance and various voltammetric techniques. Significant findingsBased on the results, our NZO/h-BN/GCE sensor exhibited high conductance, appreciable linear ranges, low detection limit (0.002 μM), optimal sensitivity (2.149 µA µM−1 cm−2), and high selectivity with good repeatability, and reproducibility results. Furthermore, the practical utility of the sensor was studied by monitoring FU in human and environmental samples. Based on the outcomes, our NZO/h-BN/GCE is a promising electrochemical platform for the detection of FU.

Magnetic Nanoparticle Support with an Ultra-Thin Chitosan Layer Preserves the Catalytic Activity of the Immobilized Glucose Oxidase.

Here, we developed magnetically recoverable biocatalysts based on magnetite nanoparticles coated with an ultra-thin layer (about 0.9 nm) of chitosan (CS) ionically cross-linked by sodium tripolyphosphate (TPP). Excessive CS amounts were removed by multiple washings combined with magnetic separation. Glucose oxidase (GOx) was attached to the magnetic support via the interaction with N-hydroxysuccinimide (NHS) in the presence of carbodiimide (EDC) leading to a covalent amide bond. These steps result in the formation of the biocatalyst for D-glucose oxidation to D-gluconic acid to be used in the preparation of pharmaceuticals due to the benign character of the biocatalyst components. To choose the catalyst with the best catalytic performance, the amounts of CS, TPP, NHS, EDC, and GOx were varied. The optimal biocatalyst allowed for 100% relative catalytic activity. The immobilization of GOx and the magnetic character of the support prevents GOx and biocatalyst loss and allows for repeated use.

Oxygen Electroreduction Reaction on Iron, Nitrogen-doped Nanocarbons: Structure – Reactivity Relationship

Theoretical calculations at the revPBE0-D3(PCM)/def2-TZVP level were performed to investigate the mechanism of the oxygen reduction reaction (ORR) on the FeN4-doped NCMs (graphene, single-walled (6,6)-armchair and (12,0)-zigzag carbon nanotubes) as catalysts. The effect of the support and relative orientation of FeN4 fragment in the catalyst structure on the ORR activity and stability of the differently adsorbed successive intermediates (O2*, HO2*, O*, HO*, H2O2*, H2O*) is discussed. Special attention is given to the possible poisoning effect of CO. The relative catalytic activity of the metal center and the adjacent C2 site of the carbon support are analyzed depending on the structure of the support. The metal catalytic center on the armchair nanotube and graphene supports is prone to deactivation by poisoning with CO, whereas in the zigzag nanotube supported catalyst the metal center is tolerant to CO. The four-electron mechanism of ORR is shown to be preferable over the two-electron mechanism in both acidic and alkaline media, both on the metal and C2 centers.

Construction of Double-enzyme Complexes with DNA Framework Nanorulers for Improving Enzyme Cascade Catalytic Efficiency.

Efficient biocatalytic cascade reactions play a crucial role in guiding intricate, specific and selective intracellular transformation processes. However, the catalytic activity of the enzyme cascade reaction in bulk solution was greatly impacted by the spatial morphology and inter-enzyme distance. The programmability and addressability nature of framework nucleic acid (FNA) allows to be used as scaffold for immobilization and to direct the spatial arrangement of enzyme cascade molecules. Here, we used tetrahedral DNA framework (TDF) as nanorulers to assemble two enzymes for constructing a double-enzyme complex, which significantly enhance the catalytic efficiency of sarcosine oxidase (SOx)/horseradish peroxidase (HRP) cascade system. We synthesized four types of TDF nanorulers capable of programming the lateral distance between enzymes from 5.67 nm to 12.33 nm. Enzymes were chemical modified by ssDNA while preserving most catalytic activity. Polyacrylamide gel electrophoresis (PAGE), transmission electron microscopy (TEM) and atomic force microscopy (AFM) were used to verify the formation of double-enzyme complex. Four types of double-enzyme complexes with different enzyme distance were constructed, in which TDF26(SOx+HRP) exhibited the highest relative enzyme cascade catalytic activity, ~3.11-fold of free-state enzyme. Importantly, all the double-enzyme complexes demonstrate a substantial improvement in enzyme cascade catalytic activity compared to free enzymes.

Immobilization of nano-Cu on ceramic membrane by dopamine assisted flowing synthesis for enhanced catalysis

Catalytic membranes containing metal nano-catalysts are effective in removing organic pollutants from wastewater. The relative low catalytic activity of the non-noble metals (such as Cu nanoparticles) presents a challenge for their widespread application. Herein, Cu nanoparticles were in-situ immobilized on ceramic substrate by a dopamine assisted flowing synthesis method to strengthen its catalytic property. Firstly, a precursor solution containing dopamine and Cu2+ was cyclically permeated through the ceramic microfiltration substrate to form a polydopamine coating with chelated Cu2+. Then, Cu nanoparticles were in-situ formed with the aid of NaBH4. FESEM, EDS, XPS and XRD analyses demonstrate the successful formation of the Cu nanoparticles. The obtained membrane depicts good hydrophilicity and permeability (556.51 L m-2h−1 at 0.1 MPa). In the continuous catalytic degradation under cross-flow filtration mode, the membrane achieves 90.84 % reduction of 4-nitrophenol (4-NP) and 92.36 % degradation rate of methyl orange (MO). The large amount of Cu nanoparticles immobilized within the membrane pores (form inner-pore microreactors) enhance the catalytic activity of the membrane, resulting in an apparent reaction rate constant of 38.78 min−1 on the permeation side. The composite membrane has good antifouling and easy-cleaning properties (the flux recovery rate is 84.3 %). In long-term experiments, the catalytic degradation rate of MO remains above 96 % throughout 50 cycles, demonstrating good stability. This study provides a novel strategy for developing catalytic membrane with immobilized non-noble metal nanoparticles, which has potential applications in environmental remediation.

‘Homeopathic’ palladium catalysis? The observation of distinct kinetic regimes in a ligandless Heck reaction at (ultra-)low catalyst loadings

The catalytic behaviour of ‘ligandless’ palladium(II) acetate in the Heck arylation reaction of iodobenzene with methyl acrylate is examined at (ultra-)low catalyst loadings using in situ spectroscopy. The study reveals two distinctive kinetic regimes with distinct Pd orders. A simplified microkinetic model revealed the presence of at least two kinetically competent catalysts, represented by a monomeric (Pd1) and dimeric (Pd2) species. The relative catalytic activity and deactivation rates for both species can also be estimated from the experimental results. This work provides direct kinetic evidence that a higher-order Pd species can be more active than a monomeric species, and the key role played by catalyst deactivation, particularly at higher catalyst loadings. This implies that lowering the catalyst loading may be an effective strategy to combat catalyst deactivation without necessarily incurring significant deterioration in reaction rate.

Bound lipase: an important form of lipase in rice bran (Oryza sativa)

Rice bran residue possessed a steady lipase activity ((26.68 ± 3.69)%) after its endogenous lipase was extracted continuously by phosphate buffer solution (PBS) for 24 h. Therefore, the aim of this research was to explore whether there exist any bound lipases in rice bran (Oryza sativa). Three physical treatments (grinding, homogenizing and ultrasound crush) and 6 enzymatic treatments (cellulase, hemicellulase, pectinase, complex cellulase, glucoamylase and α-amylase) were applied to rice bran in order to investigate this bound lipase. The relative catalytic activities of extraction supernatant and residue for pectinase group were (437.63 ± 22.54)% and (159.26 ± 2.12)%, respectively, which were significantly higher (P < 0.05) than other groups. This phenomenon demonstrated that lipase was the most likely to combine with pectin. Molecular simulation proved that pectin could combine with two rice bran lipases (lipase 315 and lipase 308) and cover the catalytic centers so as to prevent the lipases from encountering the substrate and inhibiting their catalytic activities. During combination, pectin could make the lipases more compact and reduce the solvent accessible surface area of lipases, which would make the lipases inactive to molecular interaction. In summary, part of rice bran lipase was proved to exist in bound form and combined with the pectin.

Bio-compatible n-HAPs/polymer monolithic composites templated from CO2-in-water high internal phase emulsions

According to the applications of materials in food and biology etc. fields, the open-cell macroporous polymer composite must contain a non-toxic component, and be bio-compatible, and the preparation processes should be green and facile. Herein, bio-compatible macro-porous nano-hydroxyapatite particles (n-HAPs)/polymer monolithic composites were templated from green and facile CO2-in-Water high internal phase emulsion (C/W HIPE). The bio-active n-HAPs that acted as emulsifiers were incorporated, which enable the well-dispersion of functional fillers in these monolithic composites. Green and facile C/W HIPE templating combined with radical polymerization of bio-compatible monomers involves nontoxic chemicals, and produced polymer monolith with macro-porous open-cell structure (80–120 μm in pore size, 20–40 μm in pore-throat size), and enable the n-HAPs/polymer improved flexibility and mechanical performance (above 80% compression strain, > 400 kPa of compression strength). Results of bio-compatibility tests show that these n-HAPs/polymer monoliths have non-cytotoxicity on HepG2 cells; Furthermore, the immobilization of pectinase by the composite indicates that composites have physical adsorption of pectinase, and the introduction of n-HAPs is more conducive to the immobilization of pectinase and the improvement and maintenance of enzyme activity; after reusing the immobilized pectinase 10 times, the relative catalytic activity can still be above 85%. Therefore, this kind of porous composite has promising potential in applications of bio-tissue engineering, food, and pharmaceutical.

Photocatalytic dye degradation by magnetic XFe2O3 (X: Co, Zn, Cr, Sr, Ni, Cu, Ba, Bi, and Mn) nanocomposites under visible light: A cost efficiency comparison

Magnetic photocatalyst-based dye degradation under visible light is a promising approach due to the ease of catalyst separation and recycling provided the catalyst is robust and cost-effective. To scrutinize and find a highly efficient and cost-effective magnetic photocatalyst, we have synthesized a series of X metal-doped Iron oxide-based nanocomposites XFe2O3 [X = Cobalt(Co), Zinc(Zn), Chromium(Cr), Strontium(Sr), Nickel(Ni), Cupper(Cu), Barium(Ba), Bismuth(Bi) and Manganese(Mn)] by simple precipitation based large scale feasible synthetic procedures. Afterward, those were meticulously characterized by various techniques such as UV–vis, Raman, Fourier Tranform Infrared Spectroscopy (FT-IR), Powder X-ray Diffraction (P-XRD), Transmission Electron Microscope (TEM), Scanning Electron Microscope (SEM) and Vibrating Sample Magnetometer (VSM). The magnetic susceptibility measurements showed that these XFe2O3 nanocomposites are ferromagnetic at room temperature. We tested their efficacy for photocatalytic dye (Methylene Blue) degradation under visible light irradiation and found that they can all be active at different pHs. Under natural sunlight also, the photocatalytic efficiency of ZnFe2O3 and CuFe2O3 for the removable of Methyl Orange was much higher than all other catalysts. A comparison of their relative cost and catalytic activity was plotted and BaFe2O3, MnFe2O3 and ZnFe2O3 were found to be the best magnetic photocatalysts for dye degradation under visible light while under sunlight, ZnFe2O3, CuFe2O3 and BaFe2O3 were found to be the best magnetic photocatalysts. The proposed formula clearly shows that, in addition to the percentage of degradation, the pricing of the catalyst is a crucial aspect to consider when selecting a catalyst. We also found that by maintaining the correct pH, the percentage of degradation increased efficiently.

Metal-based micro-composite of L-arabinose isomerase and L-ribose isomerase for the sustainable synthesis of L-ribose and D-talose

The biocatalysts are broadly explored in the biological transformation processes. The enzyme cascade catalysis involves various catalytic activities in a sequential process to produce the desired product including the formation of reaction intermediates. Enzyme immobilization is a method in which enzymes are confined within a support or matrix either physically or chemically to enhance their relative stability and catalytic activity in the enzyme cascade catalysis. In view of this, L-arabinose isomerase (L-AI) and L-ribose isomerase (L-RI) were immobilized on zeolite based metal framework as a micro-composite construct (DEMC@L-AI+L-RI) using linker, and metal ions. Such immobilization could be of great significance and provide several advantages like mesoporous surface for enzyme adsorption, desirable functionality in the production of products in enzyme cascade reaction, high storage stability and enhanced recyclability. The developed DEMC@L-AI+L-RI was characterized using SEM, FTIR, CLSM and TGA. The immobilization yield was 32% and loading of enzyme was 22% on the surface of micro-composite. The DEMC@L-AI+L-RI showed relatively stable catalytic activity at pH 5–6 and temperature 40 °C. The catalytic efficiency (kcat/Km) of both the enzymes was increased by 1.5-fold after immobilization. With the immobilized biocatalyst, bioconversion of L-arabinose to L-ribose was 22.6% and D-galactose to D-talose was 15.2%. The reusability of developed biocatalyst for more than six cycles was observed for more than 50% yield of the sugars. The conversion of biomass sugars from beetroot and onion waste residues was 20% and 14% to produce ribose and talose, respectively.

Nanometer-thick defective graphene films decorated with oriented ruthenium nanoparticles. Higher activity of 101 vs 002 plane for silane-alcohol coupling and hydrogen transfer reduction

Pyrolysis of ammonium alginate films containing Ru(NH3)6Cl3 leads to the formation of Ru nanoparticles (NPs) supported on defective graphene films. The procedure allows controlling the preferential facet orientation of small Ru NPs (5–20 nm), either 002 when the pyrolysis is carried out under Ar atmosphere or the 002 and 101 planes for pyrolysis in the presence of H2. Ru is a metal difficult to prepare in preferential facet orientation compared to noble metals due to its higher reactivity and smaller particle size. Theoretical calculations substantiated the inhibition of Ru(002) growth by H2 adsorption, with restructuration to Ru(002–101) NPs. The defective graphene films of about 15 nm thickness containing one of the two types of Ru NPs (150 ng/cm2) exhibit distinctive catalytic activity for the dehydrogenative coupling of silanes and alcohols and hydrogen transfer reduction of cyclohexanone. Comparison of turnover frequencies indicates that the 101 facet is more efficient than the 002 plane. Overall, this study illustrates that pyrolysis conditions can control the preferential crystallographic orientation of the growing Ru NPs and the relative catalytic activity of their specific crystallographic planes.

Halonium, chalconium, and pnictonium salts as noncovalent organocatalysts: a computational study on relative catalytic activity.

This theoretical study sheds light on the relative catalytic activity of pnictonium, chalconium, and halonium salts in reactions involving elimination of chloride and electrophilic activation of a carbonyl group. DFT calculations indicate that for cationic aromatic onium salts, values of the electrostatic potential on heteroatom σ-holes gradually increase from pnictogen- to halogen-containing species. The higher values of the potential on the halogen atoms of halonium salts result in the overall higher catalytic activity of these species, but in the case of pnictonium and chalconium cations, weak interactions from the side groups provide an additional stabilization effect on the reaction transition states. Based upon quantum-chemical calculations, the catalytic activity of phosphonium(V) and arsenonium(V) salts is expected to be too low to obtain effective noncovalent organocatalytic compounds, whereas stibonium(V), telluronium(IV) and iodonium(III) salts exhibit higher potential in application as noncovalent organocatalysts.

The Electro-oxidation of Hydrazine with Palladium Nanoparticle Modified Electrodes: Dissecting Chemical and Physical Effects: Catalysis, Surface Roughness, or Porosity?

Palladium nanoparticles in the form of a layer on the surface of an electrode are shown to be electrocatalytic with respect to the four-electron oxidation of hydrazine to form dinitrogen. Quantitative voltammetry shows that the reduced overpotential in comparison with both carbon and bulk palladium electrodes partly arises from the increased surface area of the interface and partly from an increased catalytic activity of the nanoparticles relative to the bulk material. The relative catalytic activity per unit surface area of the nanoparticles as compared with the bulk material is shown to be ca. 35-45.

Effect of iron-based catalyst from coal liquefaction on coal char gasification reactivity and kinetics

Gasification technology can help the resource recovery of solid product from coal liquefaction, where the iron-based catalyst widely exists. In the present work, the effects of iron-based catalysts from coal liquefaction on the coal structure and reactivity were studied, using the Hami raw coal and demineralized coal. The surface morphology, element distribution and mesoporous characteristics of coal char were investigated by SEM-EDS and physical adsorption analyzer. The gasification reactivity was performed in a thermogravimetric analyzer. The gasification kinetics was studied through the model-fitting and model-free methods. The results showed that the demineralization and catalyst loading had more obvious effect on the surface attachments than the carbon matrix. The coal char with catalyst loading had significant larger specific surface area (SSA). The reactivity improvement by iron-based catalyst could be attributed to the enrichment of Fe and AAEMS and increase of SSA for coal char. More pronounced relative catalytic activity was observed for the catalytic gasification of demineralized coal char, and its activity was not sensitive to the change of heating rate and carbon conversion. The gasification characteristics difference would be reduced with the increase of heating rate. The iron-based catalyst can increase the pre-exponential factor A for the demineralized coal char gasification, and reduce the activation energy Ea for the raw coal char gasification. Under non-isothermal conditions, the Ea decreased with conversion. According to fitting performance and kinetic compensation effect, the random pore model was the best model to describe gasification, especially for the (catalytic) gasification of the demineralized coal char.

Performance of lactase encapsulated in pectin-based hydrogels during lactose hydrolysis reactions

The aim of this work was to evaluate the performance of lactase encapsulated in pectin-based hydrogels during lactose hydrolysis reactions. Pectin-based hydrogel and pectin-based composite hydrogel containing pine fiber were synthesized by chemical cross-linking. Lactase was encapsulated in both hydrogels by adsorption. Lactose hydrolysis experiments were conducted by immersing encapsulated lactase in standard lactose solutions, varying pH and temperature. The formed glucose concentrations were determined by UV–vis spectrophotometry, using an enzymatic-colorimetric method. The lactase encapsulation, catalytic activity, lactose hydrolysis and lactase release were affected by the drying of the hydrogel (oven or freeze-drying), pH and temperature variation of the aqueous lactose solution and pine fiber content in the polymer network. The encapsulation efficiencies of lyophilized hydrogels containing 0, 5 and 10% of pine fiber were 69.04 ± 1.19, 69.57 ± 0.78 and 71.10 ± 0.35%, respectively. Slightly lower values were found for air-dried hydrogels. The relative catalytic activities of lactase encapsulated in the hydrogels containing 0, 5 and 10% of pine fiber were, respectively, 52.85 ± 0.97, 56.26 ± 1.07 and 57.27 ± 1.18% (w/w) after three successive cycles of lactose hydrolysis in UHT-milk. Overall, pectin-based hydrogels are potential solid supports for preserving the lactase activity during lactose hydrolysis reactions.

Fenton-like reaction-induced degradation of Methylene Blue by using supermacroporous ferrimagnetic nanorings

The removal and/or degradation of methylene blue (MB) from dyestuff wastewater has attracted widespread attention. Utilization of environmental purification nanomaterials is an effective means in the field of environmental remediation, and degradation efficiency under different circumstances is always a high priority for the nanoagents. In this study, uniform supermacroporous ferrimagnetic Fe3O4 nanorings (sFe3O4-NRs) were fabricated for high-efficiency MB degradation. Typically, the sFe3O4-NRs were prepared by a convenient hydrothermal method. Subsequently, the morphology structure of the sFe3O4-NRs was characterized by scanning electron microscope (SEM), transmission electron microscope (TEM) and highresolution transmission electron microscopy (HRTEM), respectively. Next, a Fenton-like reaction-induced MB degradation was performed in the present of sFe3O4-NR nanocatalysator and hydrogen peroxide (H2O2). Meanwhile, the sFe3O4-NRs showed excellent Fenton-catalytic activity for degradation of MB in a wide range of pH (3-11). Moreover, because of the magnetic property of the sFe3O4-NRs (saturation magnetization of 34.26 emu/g), the used sFe3O4-NR could be rapidly separated from the reaction medium by using a magnet, the sFe3O4-NR resented relative high catalytic activity even after 10 times reuse. The main conclusion from this work was that the as-synthesized sFe3O4-NRs nanoagent was a type of desirable Fenton catalyst to degenerate MB from wastewater.

Theoretical insights into furfural reduction to furfuryl alcohol via the catalytic hydrogen transfer reaction catalyzed by cations exchanged zirconium-containing zeolites

The density functional theory has been employed to study the reduction of furfural to furfuryl alcohol via the catalytic transfer hydrogenation (CTH) reaction over cations exchanged zirconium (Zr) containing zeolites. From the calculations results, the reaction proceeds through the following three steps: (i) the dissociation of the hydroxyl (OH) group of i-propanol to form i-propoxide, (ii) the hydrogen transfer from i-propoxide to furfural and (iii) the formation of furfuryl alcohol. The Li-Zr-BEA zeolite shows higher catalytic activity than Li-Sn-BEA due to its lower activation free energy (25.8 vs 20.8 kcal/mol). The effect of cations (Li, Na and K) which are exchanged on Zr-BEA is also considered. Based on the activation energy of rate determining step and turn over frequencies (TOFs), the catalytic activity rises when the group period of an exchanged metal decreases. The finding shows that the exchange of cations in Zr-zeolite surface is a simple process to make a tunable catalyst for the catalytic transfer hydrogenation reaction. The effects of different zeolite frameworks (BEA, ZSM-5 and FAU) are also studied. The relative catalytic activity of Li-Zr-BEA and Li-Zr-ZSM-5 zeolite is found to be almost similar and higher than that of Li-Zr-FAU zeolite.

Lipase-Immobilized Cellulosic Capsules with Water Absorbency for Enhanced Pickering Interfacial Biocatalysis.

Lipase-immobilized cellulosic capsules consisting of hydrophobic ethyl cellulose (EC) and hydrophilic carboxymethyl cellulose (CMC) were developed with a promising interfacial activity and water absorbency for the enhanced Pickering interfacial biocatalysis. Lipase was physically immobilized with water-absorbent materials (CMC) via hydrogen bonding and electrostatic interactions and acted as the interior catalytic core of the capsule. The interfacially active EC worked as the exterior shell, enabling capsules to stabilize the oil-in-water Pickering emulsion for the subsequent Pickering interfacial catalysis. The capsules with CMC created interior water-rich conditions to improve the conformational and enzymatic activity of the immobilized lipase. Compared with capsules without water-absorbent materials, the capsules with CMC enhanced the efficiency of the Pickering interfacial catalysis for the esterification of oleic acid and 1-octanol by 12%. Immobilized with a small amount of lipase (0.0625 g/g), the cellulosic capsules with water absorbency could convert 50.8% of the reactants after 10 h under room temperature, significantly higher than that by the same amount of free lipase in the biphasic system (15%) and a Pickering emulsion (24.1%) stabilized by empty capsules (without lipase). Moreover, the cellulosic capsules could be recycled by simple centrifugation while retaining their high relative catalytic activity for at least eight cycles, demonstrating their sustainable catalytic performance.

Theoretical Density Functional Theory Study of Electrocatalytic Activity of MN4-Doped (M = Cu, Ag, and Zn) Single-Walled Carbon Nanotubes in Oxygen Reduction Reactions.

The mechanism of oxygen reduction reaction (ORR) on transition metal-doped nitrogen codoped single-walled nanotubes, C114H24MN4 (MN4-CNT where M = Zn, Cu, or Ag; N = pyridinic nitrogen), has been studied with the density functional theory method at the ωB97XD/DGDZVP level of theory. The charge density analysis revealed two active sites of the catalyst toward ORR: the MN4 site and the C=C bond of the N–C=C–N metal-chelating fragment (C2 site). The structure of O-containing adsorbates (O2*, HOO*, O*, HO*, etc.) on the two sites and the corresponding adsorption energies were determined. The analysis of the free energy diagrams allows to conclude that the 4e– mechanism of ORR is thermodynamically preferable for all the studied catalysts. The probability of the 2e– mechanism of ORR with the formation of hydrogen peroxide decreases in the order Cu > Ag > Zn. The most and the least exergonic steps of the conventional 4e– mechanism of ORR on each active site of model catalysts as well as the electrode potentials of deceleration and of maximum catalytic activity in both acidic and alkaline media are determined. The relative catalytic activity toward ORR increases in the order Zn < Ag ≪ Cu and is mainly attributed to the C2 site rather than the MN4 site, while combined catalytic activity of the two sites (AgN4/C2 sites) is predicted for the AgN4-CNT catalyst.

Ruthenium(II) complexes bearing thioether-azoimine tridentate SNN donor ligands: Synthesis, spectroscopic properties, structural characterization, electrochemistry, and catalytic activity

Ruthenium(II) solvato complexes with tridentate (SNN) thioether-azoimine ligands having the general formula trans-[Ru(L1)(Y)Cl2] (1-2) {L1 = 2-PhS(C6H4)N=NC=(COCH3)-NC6H5, Y= DMF (1); Y= acetonitrile (2)} and trans-[Ru(L2)(Y)Cl2] (3-4) {L2 = 2-CH3S(C6H4)N=NC=(COCH3)-NC6H5, Y =DMF (3); Y= acetonitrile (4)} have been synthesized and characterized by various spectroscopic (IR, UV–Vis and 1H NMR) techniques. The complexes exhibit a quasi-reversible one electron Ru(II)/Ru(III) oxidation couple around 1.35 V for Ru(III/II) and a reduction couple around -0.35 V for L(0/-). Catalytic activity of the compounds has been investigated for the hydrogenation of acetophenone. The relative catalytic activity was rationalized using calculated thermodynamics parameters of the partial dissociation of the complexes to give solvent (acetonitrile or DMF) and the rest of the complex. Geometry has been confirmed by single crystal X-ray study. The electronic structure, redox properties, electronic excitations and catalytic activity for the complexes are interpreted by density functional theory (DFT) calculations.