Electrocatalytic hydrogenation of catechol on Rh–Al2O3 in different media — pH-Dependent reduction mechanism for intermediate formation

2006 ◽  
Vol 84 (12) ◽  
pp. 1640-1647 ◽  
Author(s):  
Anne Brisach-Wittmeyer ◽  
Nicolas-Alexandre Bouchard ◽  
Raymond Breault ◽  
Hugues Ménard
Keyword(s):  
Cyclic Voltammetry ◽  
Uv Spectroscopy ◽  
Aqueous Media ◽  
Intermediate Formation ◽  
Vitreous Carbon ◽  
Reduction Mechanism ◽  
Electrocatalytic Hydrogenation ◽  
Vis Spectroscopy ◽  
Ph Dependent ◽  
Henry Constants

The electrocatalytic hydrogenation of catechol was carried out in aqueous media in different pH ranges with Rh–Al2O3 powder catalyst. The reactions were conducted in an H-cell used as a dynamic cell, with a reticulated vitreous carbon electrode in contact with the catalyst powder as the working electrode. It was shown that the final product is 1,2-cyclohexanediol (cis and trans isomers) and that several intermediates are detected depending on the pH of the solution. Different media, from pH 5 to 13, were studied. One of the intermediates is 1,2-cyclohexanedione, detected at all pH values. The other is 2-hydroxycyclohexan-1-one, only observed at pH ≤ 7. To determine the mechanism of the reactions involved, the electrocatalytic hydrogenation of these intermediates to form the final 1,2-cyclohexanediol product was also conducted, and their UV spectroscopy and cyclic voltammetry data recorded. The influence of the nature of the solution was screened by measuring the Henry constant of each molecule.Key words: electrocatalytic hydrogenation of catechol, pH-dependent reduction mechanism, UV–vis spectroscopy, cyclic voltammetry, Henry constants.

Experimental and computational investigation of the electrocatalytic hydrogenation of phenol in an electrochemical cell

2004 ◽  
Vol 82 (5) ◽  
pp. 641-648 ◽  
Author(s):  
A Chagnes ◽  
F Laplante ◽  
F Kerdouss ◽  
P Proulx ◽  
H Ménard
Keyword(s):  
Fluidized Bed ◽  
Cathodic Polarization ◽  
Volume Fraction ◽  
Fluid Dynamic ◽  
Aqueous Media ◽  
Vitreous Carbon ◽  
High Porosity ◽  
Electrocatalytic Hydrogenation ◽  
Reticulated Vitreous Carbon ◽  
Fluidized Bed Electrode

The electrocatalytic hydrogenation (ECH) of phenol was carried out in aqueous media with a commercial Pd/Al2O3 (5% w/w) catalyst. A porous matrix of reticulated vitreous carbon (RVC) was used to study the porosity – stirring speed coupling (PSSC) effect on the phenol hydrogenation to form cyclohexanone and cyclohexanol. In accordance with the PSSC, the electrode can act as a fluidized bed electrode or as an agglomerated electrode. Fluidized bed electrodes develop for low porosity matrices (10–30 ppi, ppi = pores per inch) at high stirring speeds (>600 rpm), while agglomerated electrodes are obtained for high porosity matrices (60–100 ppi) with moderate stirring speeds under cathodic polarization. The distribution of the volume fraction of the particles and the agglomeration of the particles have been simulated by computational fluid dynamic (CFD) methods with FLUENT software. For the agglomerated electrode, the numerical simulations demonstrate the beneficial contribution of the cathodic polarization to the agglomeration process. However, at 650 rpm, for the fluidized bed electrode, the volume fraction of the particles in the RVC does not account for the distinction in the ECH efficiency between the 30 ppi matrix and the 100 ppi matrix. For a given amount of Pd/Al2O3 catalyst, it is observed that the ECH rates depend on the PSSC and increase in the following order: 100/650 < 30/650 < 100/200. Key words: electrocatalytic hydrogenation (ECH), CFD, fluid mechanics, porous media, powder, porosity – stirring speed coupling (PSSC), reticulated vitreous carbon (RVC).

Considerations about phenol electrohydrogenation on electrodes made with reticulated vitreous carbon cathode

2003 ◽  
Vol 81 (3) ◽  
pp. 258-264 ◽  
Author(s):  
François Laplante ◽  
Louis Brossard ◽  
Hugues Ménard
Keyword(s):  
Physical Vapor Deposition ◽  
Detrimental Effect ◽  
Aqueous Media ◽  
Vitreous Carbon ◽  
Electrocatalytic Hydrogenation ◽  
Reticulated Vitreous Carbon ◽  
Composite Powders ◽  
Agglomeration Process ◽  
Adsorption Of Organic Molecules

The electrocatalytic hydrogenation (ECH) of phenol was carried out in aqueous media with catalytic powders. The catalytic powders were composed of palladium nanoaggregates deposited on various substrates such as Al2O3, BaSO4, and BaCO3. Composite powders are trapped (upon stirring) into a reticulated vitreous carbon (RVC) matrix, allowing a rapid in situ build-up of the electrode and alleviating the use of a binder, since the latter may have a detrimental effect on the ECH. For a given amount of noble metal (5% palladium by weight), it is observed that the ECH of phenol to cyclohexanol increases in the following order: Pd/BaCO3 < Pd/BaSO4 < Pd/Al2O3. It is deduced that the ECH rate is largely dependent on the adsorption of organic molecules on the nonmetallic substrate, and a model is considered to explain such a behavior. The ECH of phenol is also feasible at a reasonable rate with composite Pd/Al2O3 (0.25% Pd by weight) powders fabricated by physical vapor deposition because the peripheral distribution of Pd nanoaggregates is favorable towards the ECH.Key words: electrocatalytic hydrogenation (ECH) of phenol, reticulated vitreous carbon (RVC), alumina-based catalyst, agglomeration process, adlineation point, adsorption.

The influence of the host–guest interaction on the oxidation of natural flavonoid dyes

2011 ◽  
Vol 76 (12) ◽  
pp. 1651-1667 ◽  
Author(s):  
Šárka Ramešová ◽  
Romana Sokolová ◽  
Ilaria Degano ◽  
Magdaléna Hromadová ◽  
Miroslav Gál ◽  
...  
Keyword(s):  
Cyclic Voltammetry ◽  
Inclusion Complex ◽  
Fluorescence Intensity ◽  
Oxidation Product ◽  
Aqueous Media ◽  
Electrochemical Methods ◽  
Redox Potentials ◽  
Decomposition Products ◽  
Degradation Processes ◽  
Bioorganic Compounds

The influence of the molecular cavity protection on degradation processes of bioorganic compounds quercetin and luteolin used as the original dyes in old tapestries was studied. The degradation processes were studied by electrochemical methods in aqueous media. The products of the exhaustive electrolysis were separated and identified by GC-MS analysis. Cyclic voltammetry characteristics indicate that the inclusion complex is formed. The inclusion affects the redox potentials of both oxidation waves related to the different dissociation forms of the flavonoid molecule. It was shown that decomposition products formed by the oxidation of quercetin are stabilized in the cavity of β-cyclodextrin, including the main oxidation product 2(3′,4′-dihydroxybenzoyl)-2,4,6-trihydroxybenzofuran-3(2H)-one. The formation of the 1:1 inclusion complex of luteolin with β-cyclodextrin is supported by the enhancement of fluorescence intensity. In the case of quercetin, a decrease of fluorescence intensity occurs when 1:1 inclusion complex with β-cyclodextrin is formed.

Synthesis, Chemical Characterisation, and DNA Binding Studies of Ferrocene-Incorporated Selenoureas

2013 ◽  
Vol 66 (6) ◽  
pp. 626 ◽  
Author(s):  
Raja Azadar Hussain ◽  
Amin Badshah ◽  
Muhammad Nawaz Tahir ◽  
Bhajan Lal ◽  
Inayat Ali Khan
Keyword(s):  
Cyclic Voltammetry ◽  
Dna Binding ◽  
Atomic Absorption Spectrophotometry ◽  
Free Drug ◽  
X Ray Diffraction ◽  
Peak Potential ◽  
Binding Studies ◽  
Vis Spectroscopy ◽  
Dna Binding Studies ◽  
And Diffusion

In this article we have presented the synthesis, chemical characterisation (by NMR and FTIR spectroscopy, atomic absorption spectrophotometry, elemental analysis, and single crystal X-ray diffraction), electrochemistry, and DNA binding studies (with cyclic voltammetry, viscometry, and UV-vis spectroscopy) of six new ferrocene incorporated selenoureas. All the six compounds interact electrostatically with DNA which was evident by a negative shift in the cyclic voltammetry peak potential of the drug–DNA adduct relative to the free drug. The drug–DNA binding constant was calculated by a decrease in peak current after the addition of DNA to the free drug. We have also reported binding site sizes and diffusion coefficients of the synthesised compounds.

scholarly journals Síntesis regioespecífica y estudio electroquímico de dos derivados carboxílicos C60 solubles en agua

2021 ◽  
Author(s):  
Juan D. Villada ◽  
Álvaro Duarte-Ruiz ◽  
Manuel N. Chaur
Keyword(s):  
Cyclic Voltammetry ◽  
Liquid Chromatography ◽  
Electronic Properties ◽  
Reaction Times ◽  
C60 Fullerene ◽  
Reduction Processes ◽  
Vis Spectroscopy ◽  
Highperformance Liquid Chromatography ◽  
Electron Transfers ◽  
Reversible Reduction

We report a new methodology for the synthesis of two highly symmetric equatorial malonate hexaadducts of C60 fullerene. The synthetic methodology is based on a series of protection and deprotection steps that allow the preparation of a fullerene [60] functionalized with six symmetrical positioned malonate addends without using complicated and expensive separation techniques (highperformance liquid chromatography, HPLC) or long reaction times. This methodology allowed us to prepare the carboxylic adducts 6 (equatorial octacarboxylic tetraadduct of C60) and 8 (equatorial dodecacarboxylic hexakisadduct of C60). As far as we  now, compound 6 has not yet been reported. We also studied the electronic properties of the main compounds by UV-Vis spectroscopy and cyclic voltammetry (CV). The reported fullerene adducts exhibited several reversible reduction processes whose electron transfers are controlled by diffusion. 

scholarly journals Removal of Chromium (VI) cation metal using Poly (N-vinyl-2-pyrrolidone)/Magnetite nanocomposite from aqueous media

2017 ◽  
Vol 13 (10) ◽  
pp. 5886-5891
Author(s):  
Padmalaya G ◽  
Sreeja BS ◽  
Radha S ◽  
Raamdheep G ◽  
Saranya J
Keyword(s):  
Magnetite Nanoparticles ◽  
Infrared Absorption Spectrum ◽  
Aqueous Media ◽  
Polyvinyl Pyrrolidone ◽  
Human Society ◽  
Promising Alternative ◽  
Chromium Vi ◽  
Ir Studies ◽  
Vis Spectroscopy ◽  
Co Precipitation

Groundwater contamination with heavy metals is considered as serious environmental hazard that affect the human society. Nano adsorbents incorporating magnetite nanoparticles provides promising alternative to facilitate removal of heavy metal ions from wastewater. The present work focuses on removal of chromium (VI) cationic metals from aqueous media using Polyvinyl Pyrrolidone (PVP)/Magnetite (Fe3O4) Nanocomposite (MNC). Magnetite nanoparticles are synthesized using chemical co-precipitation and grafted using polyvinyl pyrrolidone to form a magnetite nanocomposite. MNC were characterized with X-ray diffraction (XRD) and Infrared absorption spectrum (FT-IR) studies to affirm the formation and presence of polymeric functional groups of PVP/Magnetite nanocomposite. Batch experiments are carried out at exclusive concentration intervals to study about the adsorption efficiency of MNC on chromium (VI) cationic metal using U-Vis spectroscopy. The results obtained through adsorption studies shows the synthesized PVP/Magnetite nanocomposites has a removal efficiency of 94%.

scholarly journals Total Hyptolide of Indonesian Hyptis pectinata extracts in a various solvent using HPLC and UV-Vis spectroscopy and their toxicities

2019 ◽  
Vol 22 (6) ◽  
pp. 305-309
Author(s):  
Meiny Suzery ◽  
Siti Khumairoh ◽  
Bambang Cahyono
Keyword(s):  
Quantitative Analysis ◽  
Toxicity Test ◽  
Brine Shrimp ◽  
Uv Spectroscopy ◽  
Bioactive Compound ◽  
Dry Weight ◽  
Pure Compound ◽  
Standard Curve ◽  
Lc50 Value ◽  
Vis Spectroscopy

The bioactive compound of hyptolide has been isolated from an Indonesian plant Hyptis pectinata using various solvents. The pure compound was then used as a standard in quantitative analysis using HPLC and UV-Vis spectroscopy in ethanol (EEth), ethyl acetate (EEa), acetone (Eac) and hexane (Ehex) extract each earned 3.14%, 0.01%, 1.33% and 0.04% (dry weight per sample). The standard curve of hyptolide using UV spectroscopy has been obtained with the coefficient of relationship (r) of 0.997. However, the use of spectroscopy was not recommended for the standardization of hyptolide in the extract due to interference from other compounds that absorb the same wavelength. Furthermore, the toxicity test using the Brine Shrimp lethality test shows LC50 value of 92-181 ppm, which was in EEa compared to EEth, Eac, and Ehex.

scholarly journals Stabilization of Silver Nanoparticles by Cationic Aminoethyl Methacrylate Copolymers in Aqueous Media—Effects of Component Ratios and Molar Masses of Copolymers

Polymers ◽  
2019 ◽  
Vol 11 (10) ◽  
pp. 1647 ◽  
Author(s):  
Mikhailova ◽  
Senchukova ◽  
Lezov ◽  
Gubarev ◽  
Trützschler ◽  
...  
Keyword(s):  
Silver Nanoparticles ◽  
Analytical Ultracentrifugation ◽  
Silver Salt ◽  
Aqueous Media ◽  
Reducing Agent ◽  
Methacrylate Copolymers ◽  
Vis Spectroscopy ◽  
Cationic Copolymers ◽  
Consistent Information ◽  
Scanning Electron

The ability of aminoethyl methacrylate cationic copolymers to stabilize silver nanoparticles in water was investigated. Sodium borohydride (NaBH4) was employed as a reducing agent for the preparation of silver nanoparticles. The objects were studied by ultraviolet-visible (UV-vis) spectroscopy, dynamic light scattering (DLS), analytical ultracentrifugation (AUC) and scanning electron microscopy (SEM). Formation of nanoparticles in different conditions was investigated by varying ratios between components (silver salt, reducing agent and polymer) and molar masses of copolymers. As a result, we were successful in obtaining nanoparticles with a relatively narrow size distribution that were stable for more than six months. Consistent information on nanoparticle size was obtained. The holding capacity of the copolymer was studied.

scholarly journals Copper Complexes of Benzoylacetone Bis-Thiosemicarbazones: Metal and Ligand Based Redox Reactivity

2021 ◽  
Vol 74 (1) ◽  
pp. 34 ◽  
Author(s):  
Jessica K. Bilyj ◽  
Jeffrey R. Harmer ◽  
Paul V. Bernhardt
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Cyclic Voltammetry ◽  
Copper Complexes ◽  
Atmospheric Oxygen ◽  
The Other ◽  
Oxidation Reactions ◽  
Paramagnetic Resonance ◽  
Time Resolved ◽  
Vis Spectroscopy ◽  
Electron Paramagnetic

Bis-thiosemicarbazones derived from the β-diketone benzoylacetone (H3banR, R=Me, Et, Ph) are potentially tetradentate N2S2 ligands whose coordination chemistry with copper is reported. In the absence of oxygen and in the presence of base they form anionic CuII complexes of the fully deprotonated ligands [CuII(banR)]–. Upon exposure to atmospheric oxygen they undergo a complex series of reactions leading to two types of products; one a ligand oxidised ketone complex [CuII(banRO)] and the other an unprecedented dimeric di-CuIII complex [(CuIII(banR))2] depending on the R substituent. Time-resolved UV-vis spectroscopy, cyclic voltammetry, spectroelectrochemistry, and electron paramagnetic resonance (EPR) spectroscopy have been used to identify intermediates on the way to stable products formed under both anaerobic and aerobic conditions. It is found that both ligand-centred and Cu-centred oxidation reactions are occurring in parallel leading to this unusually complicated mixture of products.

scholarly journals Green and Traditional Synthesis of Copper Oxide Nanoparticles—Comparative Study

Nanomaterials ◽  
2020 ◽  
Vol 10 (12) ◽  
pp. 2502
Author(s):  
Obakeng P. Keabadile ◽  
Adeyemi O. Aremu ◽  
Saheed E. Elugoke ◽  
Omolola E. Fayemi
Keyword(s):  
Cyclic Voltammetry ◽  
Zeta Potential ◽  
Copper Oxide ◽  
Electrochemical Sensors ◽  
Modified Electrodes ◽  
Copper Oxide Nanoparticles ◽  
Oxide Nanoparticles ◽  
Sem Images ◽  
Redox Probe ◽  
Vis Spectroscopy

The current study compared the synthesis, characterization and properties of copper oxide nanoparticles (CuO) based on green and traditional chemical methods. The synthesized CuO were confirmed by spectroscopic and morphological characterization such as ultraviolet-visible (UV-vis) spectroscopy, fourier transform infrared (FTIR) spectroscopy, zeta potential, scanning electron microscopy (SEM) and energy dispersed X-ray (EDX). Electrochemical behavior of the modified electrodes was done using cyclic voltammetry (CV) in ferricyanide/ferrocyanide ([Fe(CN)6]4−/[Fe(CN)6]3−) redox probe. As revealed by UV spectrophotometer, the absorption peaks ranged from 290–293 nm for all synthesized nanoparticles. Based on SEM images, CuO were spherical in shape with agglomerated particles. Zeta potential revealed that the green CuO have more negative surface charge than the chemically synthesized CuO. The potential of the green synthesized nanoparticles was higher relative to the chemically synthesized one. Cyclic voltammetry studies indicated that the traditional chemically synthesized CuO and the green CuO have electrocatalytic activity towards the ferricyanide redox probe. This suggests that the green CuO can be modified with other nanomaterials for the preparation of electrochemical sensors towards analytes of interest.

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