Electrocatalytic mechanism for formaldehyde oxidation on the highly dispersed gold microparticles and the surface characteristics of the electrode

Electrocatalytic mechanism for the electrochemical oxidation of formaldehyde (HCHO) on the highly dispersed Au microparticles electrodeposited on the surface of the glass carbon (GC) electrode in the alkaline Na2CO3/NaHCO3 solution and the surface characteristics of the Au microparticle-modified glass carbon (Au/GC) electrode were studied with in situ FTIR spectroscopy, scanning electron microscopy (SEM) and X-ray diffraction (XRD). It was found that the final products of HCHO oxidation is HCOO- at the Au/GC electrode and CO2 at the bulk Au electrode. The difference may be ascribed to the different surface characteristics between the Au/GC electrode and the bulk Au electrode. (C) 1999 Elsevier Science B.V. All rights reserved.

Cyclodextrin-catalyzed oxidation of glutathione in solution and in an ion trap

Incubated solutions containing glutathione (GSH) and alpha- or beta-cyclodextrins (CDs) were analyzed using electrospray mass spectrometry and tandem mass spectrometry, The results suggest that both CDs can catalyze oxidation of GSH to the oxidized glutathione (GSSG). The collision-induced dissociation (CID) of the 1:1 and 1:2 (CD/GSH) and 1:1 (CD/GSSG) complexes reveals the strong interactions of the CDs with the peptides tested. The 1:2 (CD/GSH) complex is considered to be the oxidation reaction intermediate, which indicates that the three-dimensional structure of the complexed two GSHs in CD complexes Is different from that of the proton-bound GSH dimer, The oxidation product, GSSG, Is also observed in the CID spectrum of the singly charged 1:1 (CD/GSH) complex, suggesting that a complex ion-complex ion reaction occurs by forming a doubly charged complex dimer, as a result of the ability of ion trap to accumulate and activate ions. The observations indicate that ion trap mass spectrometry can be used to explore cyclodextrin-catalyzed reactions and to carry out complex gaseous chemistry research. Copyright (C) 1999 John Wiley & Sons, Ltd.

Electrocatalytic oxidation of methanol at the titanium oxide electrode modified with Pt microparticles

The electrocatalytic oxidation of methanol at the Titanium oxide (TiOx, x<2) film modified with Pt microparticles has been studied. The results show that the modified electrodes exhibit a significant electrocatalytic activity and good stability for the oxidation of methanol. Under the optimal conditions, the peak current density at 0.58 V for the oxidation of methanol in the positive-going sweep is about 526 mA/cm(2) at the scan rate of 5 mV/s in 0.5 mol/L CH3OH and 0.5 mol/L H2SO4 solution and the over potential of the methanol oxidation at the modified electrode increases about 30 similar to 40 mV after 70 minutes at the current density of 100 mA/cm(2) and 50 mA/cm(2). The enhanced electrocatalytic activity and good stability are ascribed to the high dispersion of Pt microparticles in and on the TiOx film and the synergistic effect between Pt microparticles and TiOx.

In situ microscopic FTIR spectroelectrochemistry study of oxidation of L-ascorbic acid in polymer electrolyte (PEG/LiClO4)

In situ microscopic FTIR spectroelectrochemistry behavior of L-ascorbic acid (H(2)A) in polymer electrolyte is reported for the first time. H(2)A undergoes a two-step oxidation, The oxidation waves shift towards more anodic potential values when the scan rate increases. The peak currents of the oxidation waves are proportional to the square roots of scan rate up to 100 mV/s, The in situ infrared spectra suggest that the product of the oxidation be dehydroascorbic acid, which may exist as a dimer.

Electrocatalytic oxidation of hydrazines at a 4-pyridyl hydroquinone self-assembled platinum electrode and its application to amperometric detection in capillary electrophoresis

4-Pyridyl hydroquinone on a platinum electrode adsorbs through the pyridine nitrogen forming stable self-assembled layers. The electrocatalytical oxidation of hydrazines was performed by the modified electrode. The overpotential of hydrazines was decreased markedly at the self-assembled monolayer (SAM) electrode. The mechanism of hydrazine oxidation was also investigated. Amperometric detection of hydrazine under zero potential (vs Ag\AgCI\sat. KCl) was exhibited by the SAM electrode used as an electrochemical detector in a flow system. (C) 1998 Elsevier Science S.A. All rights reserved.

Catalysis of hydrotalcite-like compounds in liquid phase oxidation: (II) - Oxidation of p-cresol to p-hydroxybenzaldehyde

Hydrotalcite-like compounds (HTLcs): CoMAlCO3-HTLcs (M=Cu2+, Ni2+, Mn2+, Cr3+, Fe3+), were synthesized by coprecipitation and characterized with XRD and IR. The catalysis of these HTLcs and their calcined products were studied in the p-cresol oxidation, and the effects of the temperature of HTLcs calcination, the ratio of Co/Cu, different promoters, reaction temperatures and reaction times on reaction activities were investigated. It has been found that calcined HTLcs have higher activity than uncalcined samples and mechanical mixed oxides in this reaction. The best yield was obtained from the CoCuAlCO3-HTLc (Co/Cu/Al=3:1:1) calcined at 450 degrees C. A tentative reaction mechanism was also proposed. (C) 1998 Elsevier Science B.V.

Catalysis of hydrotalcite-like compounds in liquid phase oxidation: (I) phenol hydroxylation

Hydrotalcite-like compounds (HTLcs): (CuMAlCO3)-Al-II-HTLcs, where M-II=Co2+, Ni2+, Cu2+, Zn2+ and Fe2+, were synthesized by coprecipitation and characterized with XRD and IR. The catalysis of these HTLcs was studied in the phenol hydroxylation by H2O2 in liquid phase; then the effects of the ratio of Cu/Al, reaction temperature, solvent and pH of medium were investigated. It has been found that the uncalcined HTLcs have higher activities than those of calcined samples in this reaction. The catalyst CuAlCO3-HTLcs having Cu/Al=3 efficiently oxidized phenol and gave high yields of the corresponding diphenols in appropriate reaction conditions. A tentative reaction mechanism is also proposed. (C) 1998 Elsevier Science B.V.

Catalytic oxidation of cyclohexene to cyclohexanone by a triple system in acidic aqueous acetonitrile medium

The catalytic oxidation of cyclohexene to cyclohexanone using Pd(OAc)(2)/HQ/FePc was investigated in an acidic aqueous solution of acetonitrile. The role of each component of this system in the oxidation of cyclohexene was explored by means of UV-VIS, IR, XPS spectroscopy and. cyclic voltammetry, respectively. Based on the experimental results, the mechanism of the oxidation of cyclohexene catalyzed by Pd(OAc)(2)/HQ/FePc was elucidated.

Electrocatalytic oxidation and flow amperometric detection of hydrazine at an electropolymerized 4-vinylpyridine/palladium film electrode

A poly(4-vinyl)pyridine (PVP)/Pd film electrode was constructed for the electrocatalytic detection of hydrazine. The preparation of the PVP/GC electrode was performed by electropolymerization of the monomer 4-vinylpyridine onto the surface of a glassy carbon electrode. Subsequently, palladium is electrodeposited onto the polymer modified electrode surface. The ion-exchange function of PVP polymer is helpful to this process in view of the tetrachlorapalladate anion. Compared with the Pd/GC electrode, the modified electrode displays a better mechanical stability in a flowing stream. The PVP/Pd film electrode exhibits higher sensitivity when detecting hydrazine with a detection limit of 0.026 ng (S/N=3).

The electrochemical study of oxidation-reduction properties of horseradish peroxidase

Oxidation-reduction properties of horseradish peroxidase (HRP) have been investigated by using direct electrochemical methods. Two successive separated distinct one-electron processes of HRP were obtained and the related physiological processes were described. The monolayer coverage of HRP at the electrode surface is about 50 pmol/cm(2). UV-Vis spectrophotometry and stable amperometry prove that the enzyme electrode possesses catalytic activity for H2O2 in the absence of a mediator and it might offer an opportunity to build the third generation of biosensors for analytes, such as H2O2, glucose and cholesterol etc. (C) 1997 Elsevier Science S.A.

Electrocatalytic oxidation of methanol on polypyrrole film modified with platinum microparticles

The electrocatalytic oxidation of methanol on polypyrrole (PPy) film modified with platinum microparticles has been studied by means of electrochemical and in situ Fourier transform infrared techniques. The Pt microparticles, which were incorporated in the PPy film by the technique of cyclic voltammetry, were uniformly dispersed. The modified electrode exhibits significant electrocatalytic activity for the oxidation of methanol. The catalytic activities were found to be dependent on Pt loading and the thickness of the PPy film. The linearly adsorbed CO species is the only intermediate of electrochemical oxidation of methanol and can be readily oxidized at the modified electrodes. The enhanced electrocatalytic activities may be due to the uniform dispersion of Pt microparticles in the PPy film and the synergistic effects of the highly dispersed Pt microparticles and the PPy film. Finally, a reaction mechanism is suggested.

Electrocatalytic Oxidation of Methanol on Polythionine Film Modified with Pt Microparticles

The electrocatalytic oxidation of methanol on polythionine(PTn) film modified with Pt microparticles has been studied by means of cyclic voltammetry and in-situ FTIR spectroscopy. The Pt microparticles produced by cyclic voltammetry were highly dispersed in and on the PTn film. The modified electrodes exhibit significant electrocatalytic activity for the oxidation of methano and the catalytic activity was found in dependence on the Pt loading. The linearly adsorbed CO species is the only intermediate in the oxidation of methanol and the abnormal IR spectra for adsorbed CO were observed. On such modified electrodes, adsorbed CO species derived from methanol can be readily oxidized. The enhanced electrocatalytic activity may be ascribed to the high dispersion of Pt microparticles in and on the PTn film and the synergestic effect between Pt microparticles and the polymer. From the above results, a possible reaction mechanism was proposed.

Preparation of highly dispersed gold microparticles and their electrocatalytic activity for the oxidation of formaldehyde

The electrochemical preparation of highly dispersed Au microparticles on the surfaces of glassy carbon (GC) electrodes and their electrocatalytic activities for the oxidation of formaldehyde were studied. It was found that the reduction of Au3+ to Au is controlled by diffusion and the formation mechanism of Au microparticles on the GC surfaces corresponds to an instantaneous nucleation and diffusion-controlled three dimensional growth process. The particle size is about 80-90 nm in diameter after the electrochemical ageing treatment. These highly dispersed Au microparticles have high surface areas and exhibit better electrocatalytic activity than that of bulk-form Au toward the electrochemical oxidation of formaldehyde in alkaline media.

Preparation, physico-chemical behavior and catalytic property for ammonia oxidation of perovskite like mixed oxides La2-xSrxCuO4-lambda

A series of Sr2+ doped perovskite like oxides La2-xSrxCuO4-lambda (x = 0 similar to 1) were prepared, the structure, lattice parameters, content of Cu3+, oxygen vacancies created by Sr2+ substitution and composition of these complex oxides were studied by XRD and iodic titration method. The redox ability,active oxygen species and surface image were evaluated and analyzed with TPD, TG, XPS and SEM measurements. The catalytic activity for ammonia oxidation over these oxides was tested, and the relationship among the catalytic properties, structure, nonstoichiometric oxygen,redox ability and surface behavior were correlated and some information on the mechanism of ammonia oxidation was obtained.