Renewable manganous hexacyanoferrate-modified graphite organosilicate composite electrode and its electrocatalytic oxidation of L-cysteine

Manganous hexacyanoferrate (MnHCF) supported on graphite powder was dispersed into methyltrimethoxysilane-derived gels to yield a conductive composite, which was used as electrode material to construct a renewable three-dimensional MnHCF-modifed electrode. MnHCF acts as a catalyst, graphite powder ensures conductivity by percolation, the silicate provides a rigid porous backbone, and the methyl groups endow hydrophobicity and thus limit the wetting section of the modified electrode. Cyclic voltammetry was exploited to investigate the dependence of electrochemical behavior on supporting electrolytes containing various cations. The chemically modified electrode can electrocatalytically oxidize L-cysteine, and exhibits a distinct advantage of polishing in the event of surface fouling, as well as simple preparation, good chemical and mechanical stability, and good repeatability of surface renewal.

Effect of FePc structure on the activity in the oxidation of cyclohexene catalyzed by pd (OAc)(2)/HQ/FePc

In an acidic aqueous solution of acetonitrile, the catalytic activity of the catalysts consisted of Pd(OAc)(2)/hydroquinone(HQ) with iron phthalocyanine (FePc) from various sources was obviously different in the oxidation of cyclohexene to cyclohexanone, The analysis of the FePc using IR spectroscopy, Mossbauer spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD), scanning electron microscopy(SEM) and BET surface area measurement indicated that the catalytic activity of the multicomponent catalytic system composed of iron phthalocyanines depends on the amount of mu -oxo FePc, the crystallinity and the surface structure of iron phthalocyanine.

In situ infrared spectroelectrochemical studies on adsorption and oxidation of nucleic acids at glassy carbon electrode

The adsorption and oxidation of yeast RNA and herring sperm DNA (HS DNA) at glass carbon (GC) electrode are studied by differential pulse voltammetry (DPV) and in situ FTIR spectroelectrochemistry. Two oxidation peaks of yeast RNA are obtained by DPV, whose peak potentials shift negatively with increasing pH. The peak currents decrease gradually in successive scans and no corresponding reduction peaks occur, thus indicating that the oxidation process of yeast RNA is completely irreversible. The IR bands in the 1200-1800 cm-l range, attributed to the stretching and ring vibrations of nucleic acid bases, show the main spectral changes when the potential is shifted positively, which gives evidence that the oxidation process takes place in the base residues. The oxidation process of HS DNA is similar to that of yeast RNA. The results both from DPV and in situ FTIR spectroelectrochemistry confirm that the guanine and adenine residues can be oxidized at the electrode surface, which is consistent with the oxidation mechanism of nucleic acids proposed previously. (C) 2001 Elsevier Science B.V. All rights reserved.

Surface-renewable cobalt(II) hexacyanoferrate-modified graphite organosilicate electrode and its electrocatalytic oxidation of thiosulfate

Cobalt(II) hexacyanoferrate (CoHCF) was deposited on graphite powder by an in situ chemical deposition procedure and then dispersed into methyltrimethoxysilane-derived gels to prepare a surface-renewable CoHCF-modified electrode. The electrochemical behavior of the modified electrode in different supporting electrolyte solutions was characterized by cyclic voltammetry. In addition, square-wave voltammetry was employed to investigate the pNa-dependent electrochemical behavior of the electrode. The CoHCF-modified electrode showed a high electrocatalytic activity toward thiosulfate oxidation and could thus be used as an amperometric thiosulfate sensor.

Synthesis and crystal structure of (1,3-(Bu2C5H3)-Bu-t)(2)Sm(mu-Cl)(2)Li(THF)(2)

Anhydrous SmCl3 reacts with two equal of Li(1-3-(Bu2C5H3)-Bu-t) to give a complex (1,3-(Bu2C5H3)-Bu-t)(2) Sm(mu -Cl)(2)Li(THF)(2) (C34H58Cl2LiO2Sm, M-r = 726.99), monoclinic, space group P2(1)/n, a = 10.615(2), b = 21.037(4), c = 17.166(3) Angstrom, beta = 93.60(3)degrees, V = 3825.7 (13) Angstrom (3), Z = 4, D-c = 1.262 Mg/m(3), mu = 1.699 mm(-1) and F(000) = 1508, final R = 0.0387 and wR = 0.0741 for 5320 observed[I greater than or equal to2 sigma (I)] reflections. The average Sm - C distance is 2.73 Angstrom. Sm - Cl1 and Sm - Cl2 distances are 2.719 (2) and 2. 697 (2) Angstrom, respectively. Two 1, 3-(Bu2C5H3)-Bu-t-ring centroids and two mu (2)-bridging chloride atoms around Sm atom form a distorted tetrahedron.

Reactivity of Pt/Al2O3 and Pt/CeO2/Al2O3 catalysts for partial oxidation of methane to syngas

The ceria modified Pt/CeO2/Al2O3 and Pt/Al2O3 catalysts were studied in the partial oxidation of methane to syngas. The SEM, XRD, TPR and TPD techniques were used for the catalyst characterization. The addition of ceria could enhance the Pt dispersion and decrease the Pt crystallise size; the activity and selectivity of catalyst for partial oxidation were improved significantly, and the methane total oxidation was suppressed sharply. The ceria effect was also discussed in a detailed way.

Partial oxidation of methane to syngas over Pt-Ni/Al2O3 Catalyst

The catalytic partial oxidation of methane to syngas over Ni/Al2O3, Pt/Al2O3 and a series of Pt - Ni/Al2O3 catalysts was investigated. It was found that Pt - Ni/Al2O3 catalysts exhibit higher activity and stability than Ni/Al2O3 and Pt/Al2O3. TPR and TPD methods were used to characterize Pt - Ni bimetallic interactions in the catalysts. A series of Pt - Ni/Al2O3 catalysts and unsupported Pt - Ni samples were studied by XRD and XPS. It was found the formation of Pt - Ni alloy in the Pt - Ni/Al2O3 catalysts and the enrichment of platinum on the surface of the catalysts. It is concluded that the higher activity and stability of Pt - Ni/Al2O3 catalysts were caused by Pt - Ni bimetallic interactions.

Partial oxidation of methane to syngas over Pt/A(2)O(3) and Pt/CeO2/Al2O3

The catalytic oxidation of methane to syngas has been carried out over Pt/Al2O3 and Pt/CeO2/Al2O3. It was found that the catalysts with ceria exhibit a higher activity and selectivity than those without ceria. The catalysts were characterized by means of TPR, TPD, SEM-EDX and XRD. There is a strong interaction between ceria and platinum under the reaction condition, which increase the dispersion of platinum over catalysts, preventing the sinter of the Pt particles. As a result of the synergistic;effect between Pt and ceria, the activity of Pt/Al2O3 for combustion reaction was suppressed, the activity and selectivity :For partial oxidation were improved greatly. Another role of ceria in the catalyst is the enhancing of the WGSR, which leads to the increase of the selectivity of catalyst for hydrogen and accelerating the equilibrium of the reaction.

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.

Partial oxidation of methane to synthesize gas over Ni/alpha-Al2O3 catalyst promoted by noble metals

The production of synthesis gas by partial oxidation bf methane in oxygen has been examined over Ni/alpha-Al2O3 catalyst promoted by noble metals(Rh, Ru, Pt and Pd), especially with Pt. The reactivity is considered in conjunction with the result of H-2-TPR, CO-TPD, SEM and XRD. It is found that small amount of Pt results in a great improvement of activity for the Ni/alpha-Al2O3 catalyst. The activity order is : Rh-Ni>Pt-Ni approximate to Ru-Ni>Pd-Ni, meantime the Pt improves the stability of Ni/alpha-Al2O3 catalyst except for Pd which is easy to he deactivated by carbon deposition. The results of TPD, SEM and XRD indicate that there is an interaction between Ni and Pt metals in the catalyst. The interaction increases the dispersions of Pt and Nit the presence of Pt suppresses the growth and the migration of Ni grains over the surface of the catalyst.

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 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.