RuO2 electrode surface effects in electrocatalytic oxidation of glucose

We have studied the electrocatalytic activity of RuO₂-PVC film electrodes, fabricated using RuO₂ powders prepared at five different temperatures, viz., 300, 400, 500, 600 and 700°C, for the oxidation of glucose in high alkaline media, 1 to 3 M NaOH. The RuO₂-PVC film electrodes have been first characterized in 1 to 3 M NaOH solution by cyclic voltammetry (CV) and rotating disc electrode (RDE) techniques in a wide potential range −1,100 to 450 mV (SCE), and three redox pairs representing Ru(IV)/Ru(III), Ru(VI)/Ru(IV) and Ru(VII)/Ru(VI) transitions have been identified. The voltammetric peaks at low sweep rates have been analyzed using surface activity theory formulated for interacting electroactive adsorption sites, and interaction terms have been evaluated. The total voltammetric surface charges have been analyzed as per Trassatti’s formalism with respect to their dependence on potential sweep rate, and charges associated with less accessible and more accessible surface sites have been calculated. For glucose oxidation, the results have indicated that RuO₂ (700°C)-PVC electrode shows two oxidation peaks in contrast to RuO₂ (300°C)-PVC electrode. Also, RuO₂ (700°C)-PVC electrode exhibits higher intrinsic electrocatalytic activity than the 300°C electrode, although the former possesses lower electrochemically active surface area. Additionally, kinetic analyses made from RDE results with reference to Michealis–Menten (MM) enzyme catalysis has shown that RuO₂ (700°C) electrode possesses extended glucose-sensing range in terms of MM kinetic constant, K _M , compared to other electrodes. Possible reasons for such differences in the behavior of the electrodes of different temperatures towards glucose oxidation are identified from studies on oxidation of glucose in solutions of different pH, oxidation of different glucose derivatives, and also from physicochemical results from BET, XRD, SEM, DTGA, XPS analysis of RuO₂ powder samples.     

Surface and electrocatalytic properties of well-defined and vicinal RuO2 single crystal faces

The kinetics of Cl₂ evolution from concentrated NaCl solutions on the (110) and (230) faces of RuO₂ single crystals has been investigated by determining the Tafel slope, the stoichiometric number and the reaction orders with respect to Cl^– and H⁺. The experimental parameters suggest that the mechanism is presumably similar to that put forward earlier by Krishtalik [51] for RuO₂ layers, but a step common to oxygen evolution, like the case of polycrystalline samples, is present only with the (230) face. Reasons for this difference and for the apparent lower activity of the (110) face with respect to the (230) are discussed. A detailed analysis of the surface behavior of the two faces in Cl^– free acid and alkaline solutions has also been carried out by cyclic voltammetry.Dedicated to Professor G. Horanyi on the occasion of his 70th birthday     

New insights into ethene epoxidation on two oxidized Ag[111] surfaces

Reaction mechanisms and activation energies for the complete conversion of ethene to ethene epoxide on two recently characterized oxidized Ag{111} surfaces have been determined from density functional theory. On both surfaces, epoxidation proceeds through a two-step nonconcerted mechanism via an oxametallacycle intermediate. The key implications are that both surfaces are active and that epoxidation can take place over a wide O coverage regime.     

Enantioselective electrocatalytic epoxidation of olefins by chiral manganese Schiff-base complexes

Asymmetric electrocatalytic epoxidation of olefins has been achieved with chiral manganese Schiff-base complexes immobilized on a glassy carbon electrode surface using molecular dioxygen as oxidant. The electrocatalytic system gives moderate enantiomeric excess (ee) values (65–77%) for the epoxidation of cis-stilbene, trans-stilbene and styrene. Our results indicated that the catalyst turnover number is significantly improved when the manganese complexes are immobilized on the electrode surface, which can be attributed to the suppression of the formation of inactive manganese dimer when the active metal centres are attached to the polymer network.     

Quantum chemical modelling of ethene epoxidation with hydrogen peroxide: role of catalytic sites

Ethene epoxidation with hydrogen peroxide was studied on hydroxylated binuclear metal sites, using DFT calculations at the B3LYP/6-311+G(d,p) level of theory. A decrease of the activation enthalpy of approximately 100 kJ mol(-1) was observed compared to the gas phase reaction between hydrogen peroxide and ethene. It was previously shown that micro-solvation with water reduces the activation enthalpy by approximately 77 kJ mol(-1) and only the additional 24 kJ mol(-1) can be attributed to the binuclear site. Three different metal centres were tested, Ti(iv), Si(iv) and Ge(iv), in order to investigate any specific role of the metal centre on the activation enthalpy. The results clearly show that the activation enthalpy is independent on the nature of the metal centre. This emphasises the role of the hydrogen bonded network provided by the hydroxylated metal sites, on the stabilisation of the transitions state. In ref. 1 (A. Lundin, I. Panas and E. Ahlberg, J. Phys. Chem. A, 2007, 111, 9080) it was demonstrated that, at the transition state and upon micro-solvation, the hydrogen peroxide entity becomes polarized within the hydrogen bonding network, forming a negatively-charged fragment distant from the ethene molecule and a positively-charged fragment directly involved in the oxygen insertion step. The same mechanism was found to hold also for the reaction at the binuclear catalytic site, since the required hydrogen bonding is effectively provided by the hydroxylated metal centres. This mechanism is compared to the two-step pathway which employs a metal peroxide intermediate. Both reaction channels were found to be plausible in confined environments.     

Multi-state epoxidation of ethene by cytochrome P450: a quantum chemical study.

The epoxidation of ethene by a model for Compound I of cytochrome P450, studied by the use of density functional B3LYP calculations, involves two-state reactivity (TSR) with multiple electromer species, hence "multi-state epoxidation". The reaction is found to proceed in stepwise and effectively concerted manners. Several reactive states are involved; the reactant is an (oxo)iron(IV) porphyrin cation radical complex with two closely lying spin states (quartet and doublet), both of which react with ethene to form intermediate complexes with a covalent C-O bond and a carbon-centered radical (radical intermediates). The radical intermediates exist in two electromers that differ in the oxidation state of iron; Por(+)(*)Fe(III)OCH(2)CH(2)(*) and PorFe(IV)OCH(2)CH(2)(*) (Por = porphyrin). These radical intermediates exist in both the doublet- and quartet spin states. The quartet spin intermediates have substantial barriers for transformation to the quartet spin PorFe(III)-epoxide complex (2.3 kcal mol(-)(1) for PorFe(IV)OCH(2)CH(2)(*) and 7.2 kcal mol(-)(1) for Por(+)(*)Fe(III)OCH(2)CH(2)(*)). In contrast, the doublet spin radicals collapse to the corresponding PorFe(III)-epoxide complex with virtually no barriers. Consequently, the lifetimes of the radical intermediates are much longer on the quartet- than on the doublet spin surface. The loss of isomeric identity in the epoxide and rearrangements to other products arise therefore mostly, if not only, from the quartet process, while the doublet state epoxidation is effectively concerted (Scheme 7). Experimental trends are discussed in the light of the computed mechanistic scheme, and a comparison is made with closely related mechanistic schemes deduced from experiment.     

Quantum chemical modeling of ethene epoxidation with hydrogen peroxide: the effect of microsolvation with water

Quantum chemical calculations were performed to study the mechanism of ethene epoxidation with hydrogen peroxide. The calculations were carried out at the B3LYP/6-311+G(d,p) level of theory. The applicability of this functional to the problem at hand, including basis set effects, was validated by CCSD(T) and CASSCF based multireference MP2 calculations. A mechanism was determined where hydrogen peroxide becomes polarized in the transition state upon binding to the ethene molecule. The distant hydroxide fragment of the attached hydrogen peroxide molecule becomes partly negatively charged, while the other part of the molecule involves a proton and becomes partly positively charged. In the absence of water an activation energy of 139.7 kJ mol(-1) was determined for the isolated H(2)O(2) + C(2)H(4) system. By microsolvating with water, the impact of a hydrogen-bonded network on the activation energy was addressed. A 43.7 kJ mol(-1) lowering of the activation energy, DeltaE(a), was observed when including up to 4 water molecules in the model. This effect results from the stabilization of the proton and hydroxide fragments in the transition state. The findings are discussed in the context of previous theoretical studies on similar systems. Effects of adding or removing a proton to mimic acidic and alkaline conditions are addressed and the limitations of the model in solvating the excess charge are discussed.     

A general route for RuO2 deposition on metal oxides from RuO4

A novel method for the deposition of RuO(2) from RuO(4)(g) on diverse metal oxides has been developed by grafting dopamine onto the otherwise un-reactive metal oxide surface. Oxygen evolution reaction on TiO(2) and the photoelectrochemical improvement of WO(3) by deposition of RuO(2) are just a few examples where this novel deposition method can be used.     

Pt/RuO2/CNTs纳米催化剂中RuO2含量对甲醇电催化氧化性能的影响

制备了一种新的甲醇直接燃料电池Pt/RuO2/CNTs阳极催化剂,在相同Pt负载量下,其甲醇电催化氧化活性是Pt/CNTs的3倍.采用循环伏安法研究发现Pt/RuO2/CNTs纳米催化剂中RuO2含量对甲醇电催化氧化活性有明显影响,当Pt和RuO2在碳纳米管上含量分别为15%和9.5%时,Pt/RuO2/CNTs催化剂具有最佳的甲醇电催化氧化活性.RuO2负载在碳纳米管上比电容的变化,反映了水合RuO2结构中质子与电子传输平衡的能力,分析表明,催化剂中RuO2含量不同导致电容的变化是影响甲醇电催化氧化活性的主要原因.当催化剂结构中质子与电子传输达到平衡时,催化剂比电容最大,电催化氧化活性最高.这种基于电容关联电催化剂的观点对甲醇直接燃料电池阳极催化剂的设计非常有意义.     

Bifunctional nanocrystalline MgO for chiral epoxy ketones via Claisen-Schmidt condensation-asymmetric epoxidation reactions

Design and development of a truly nanobifunctional heterogeneous catalyst for the Claisen-Schmidt condensation (CSC) of benzaldehydes with acetophenones to yield chalcones quantitatively followed by asymmetric epoxidation (AE) to afford chiral epoxy ketones with moderate to good yields and impressive ee's is described. The nanomagnesium oxide (aerogel prepared) NAP-MgO was found to be superior over the NA-MgO and CM-MgO in terms of activity and enantioselectivity as applicable in these reactions. An elegant strategy for heterogenization of homogeneous catalysts is presented here to evolve single-site chiral catalysts for AE by a successful transfer of molecular chemistry to surface metal-organic chemistry with the retention of activity, selectivity/enantioselectivity. Br?nsted hydroxyls are established as sole contributors for the epoxidation reaction, while they add on to the CSC, which is largely driven by Lewis basic O2-sites. Strong hydrogen-bond interactions between the surface -OH on MgO and -OH groups of diethyl tartrate are found inducing enantioselectivity in the AE reaction. Thus, the nanocrystalline NAP-MgO with its defined shape, size, and accessible OH groups allows the chemisorption of TBHP, DET, and olefin on its surface to accomplish single-site chiral catalysts to provide optimum ee's in AE reactions.     

不同RuO2含量对RuO2-Fe2O3催化剂氨选择性催化氧化性能的影响

采用溶胶-凝胶法（sol-gel）制备了一系列具有不同RuO₂含量的RuO₂-Fe₂O₃催化剂,并将其应用于氨选择性催化氧化（NH₃-SCO）研究中。结果表明,所有RuO₂-Fe₂O₃催化剂都表现出较好的低温活性,且RuO₂含量对催化剂的NH₃催化氧化活性影响显著。此外,利用BET、XRD、H₂-TPR和DRIFTS等表征手段研究了催化剂的物理化学性质和催化活性之间的关系。结果表明,RuO₂的加入增大了催化剂的比表面积。RuO₂与Fe₂O₃之间存在的协同效应提高了催化剂的氧化还原能力,从而提高了催化剂的氨氧化活性。同时,RuO₂含量对催化剂表面酸性影响很大,且催化剂表面主要存在Lewis酸性位点。     

Thermal risk assessment for the epoxidation of linseed oil by classical Prisleschajew epoxidation and by direct epoxidation by H2O2 on alumina

Journal of Thermal Analysis and Calorimetry - Substitution of fossil feedstock by vegetable oils is growing due to environmental constraints and oil depletion. Among the different valorization...     

热分解制备的RuO2-IrO2电极研究

本文应用XPS和电化学技术研究热分解制备RuO2-IrO2电极的电化学性能和表面性质的关系, 以探讨制备寿命长, 价格低的阳极的可能途径。     

The electronic structure of FeO 4 2− , RuO4, RuO 4 − , RuO 4 2− and OsO4 by the HFS-DVM method

The electronic structures of FeO ₄ ^2? , RuO₄, RuO ₄ ^? , RuO ₄ ^2? and OsO₄ have been investigated using the Hartree-Fock-Slater Discrete Variational Method. The calculated ordering of the valence orbitals is 2t ₂, 1e, 2a ₁, 3t ₂ andt ₁ with thet ₁ orbital as the highest occupied. The first five charge transfer bands are assigned as:t ₁→2e(v ₁), 3t ₂→2e(v ₂),t ₁→4t ₂(v ₃), 3t ₂→4t ₂(v ₄) and 2a ₁→4t ₂(v ₅). It is suggested that ad-d transition should be observed at 1.5 eV in RuO ₄ ^? and RuO ₄ ^2? .     

Dependence of RuO2-capacitive properties on preparation conditions

The effect of a small change in the preparation conditions and the consequences thereof on the capacitive properties of RuO₂ thin films are described. The oxide films are prepared using the Pechini method and the only alteration made in the procedure is to change the order of addition of reagents. The solution color changes as a consequence and also the capacitance values, from 54.8 to 33.6 F g⁻¹, for the oxides obtained after calcination. These results could be related to the calcination kinetics, which affects the lattice stress in the oxide as calculated using X-ray diffraction patterns and Rietveld analysis.     

RuO2电极的析氧活性研究

本文用XPS, UPS和电化学方法研究了RuO2电极的活怀中心组成及其在电解过程中的变化。结果表明, RuO2电极的活性中心为氧结构空位。在电解过程中,表层的氧结构空位不断减少, 由于RuO2电极析氧反应区域不断扩展和深入, 又暴露出新的氧结构空位, 但电极外表面的氧结构空位对电极析氧活性影响较大, 外表面氧结构空位为RuO2电极有效的活性中心。此外, 电极的腐蚀和剥落也是导致活性降低的原因之一。     

Syntheses and Crystal Structures of Two Sodium Ruthenates: Na2RuO4 and Na2RuO3

Na₂RuO₄, prepared from Na₂O₂ and RuO₂ via high oxygen pressure synthesis, crystallises monoclinic in space group P2₁/c (a = 10.721(6), b = 7.033(4), c = 10.871(6) Å, β = 119.10(4)°, Z = 8, 2503 unique reflections, R₁ = 0.049). Structure determination from single crystal data shows that the compound consists of infinite chains of RuO₅ trigonal bipyramids connected through their axial vertices. The Na cations connect the pseudohexagonally packed equation/tex2gif-stack-1.gif[RuO₃O_2/2] chains and are coordinated by six or seven oxygen atoms, respectively. The compound exhibits an one‐dimensional spin system with μ = 2.80 μ_B and Θ = —222 K and a three‐dimensional antiferromagnetic ordering below 50 K. Na₂RuO₃ was obtained from Na₂RuO₄ at 850 °C under a flow of argon. The structure was determined from X‐ray powder diffraction. It is closely related to the α‐NaFeO₂ and the Li₂SnO₃ structure types, layered variants of the NaCl type. In Na₂RuO₃ the Na and Ru atoms are partially disordered. This partially disordered state was approximated by a Rietveld refinement of two superimposed structural models (model I: R 3¯ m, a = 3.12360(5), c = 16.0370(4) Å, Z = 2; model II: C2/c, a = 5.4141(4), b = 9.3663(6), c = 10.8481(4) Å, β = 99.636(9)°, Z = 8).     

Adsorption of platinum on the stoichiometric RuO2(110) surface

Density functional theory was used to calculate the geometries and electronic structures of Pt adsorption on the stoichiometric RuO(2)(110) surface at different coverages. The calculated results revealed that the Pt atoms strongly adsorb on RuO(2), and two-dimensional growth up to 1.25 ML deposition is energetically favorable. At low coverage, the binding between Pt and RuO(2) is very strong, accompanied by a significant transfer of electron density from Pt to the support and a large downshift of the d-band compared to that of the unsupported Pt. At high coverage, a weak interaction of RuO(2) with the Pt cluster is observed, and the electronic structure of Pt is only slightly modified with respect to that of the unsupported material. Our results suggest that among the systems investigated, the RuO(2)-supported Pt at a coverage of 1 ML may become one of the best alternatives to pure Pt as a catalyst because it combines a high stability and a moderate activity similar to Pt.     

在TiO2纳米阵列上电沉积RuO2用于CO2电还原

传统上,RuO₂/TiO₂复合电极制备是通过在TiO₂/Ti基体上多次涂覆含Ru前驱体溶液和随后热分解（TD）来实现的. 为克服上述方法中Ru用量大和利用率低之不足, 本工作主要基于循环伏安法（CV）在TiO₂纳米管阵列（TNA）上电沉积RuO₂制备RuO₂^CV/TNA复合电极. SEM、GIXRD和CV结果表明, 电沉积的RuO₂为无定型结构, 所制备电极中的Ru用量约为传统的RuO₂^TD/TNA电极中Ru用量的1/30. 尽管两电极催化CO₂还原产物的法拉第效率接近, 但是RuO₂^CV/TNA电极比RuO₂^TD/TNA电极展示了更高的还原电流, 较正的初始还原电位和更好的稳定性. 与磷酸盐缓冲溶液中电还原CO₂相比,RuO₂^CV/TNA电极在0.1 mol•L^-1 KHCO₃中电还原CO₂除生成更高法拉第效率的甲酸根和甲烷外,还检测到CO的生成.