Showing papers by "Ch. Comninellis published in 2002"

Electrochemical promotion of conventional and bipolar reactor configurations for NO reduction

Abstract: The reduction of NO by CO or C3H6 in the presence of O2, a reaction of great technological importance, was investigated on porous polycrystalline Rh catalyst films using a single-chamber and a wireless bipolar cell configuration. In the latter case the Rh catalyst films were deposited on the inner side of a YSZ tube, while two Au films deposited on the outer side of the tubes were used to polarize the Rh catalyst surface. The experimental conditions used in this study were close to those in the exhaust of a lean burn or diesel engine, i.e., high flowrates and space velocities and in some cases, considerable excess of oxygen. It was found that both direct (conventional) and indirect (wireless) polarization of the catalyst causes significant enhancement in the reaction rates (up to a factor of 20) and in the reactant conversion. These rate increases are strongly non-Faradaic with apparent Faradaic efficiencies, A, in the order of 100, manifesting the effect of Electrochemical Promotion or Non-faradaic Electrochemical Modification of Catalytic Activity (NEMCA). The Rh catalyst films were subsequently promoted in a classical way, via dry impregnation with NaOH, followed by drying and calcination. The thus Na-promoted Rh films were found to exhibit higher catalytic activity than the unpromoted films, with a considerable decrease in their light-off temperature. The effect of Electrochemical Promotion was then studied on these, already Na-promoted Rh catalysts. The results showed that the effect of Chemical and Electrochemical Promotion on the catalyst performance can be synergetic and their combination may lead to interesting practical applications. This is further supported by the fact that such bipolar tube configurations: (a) do not need electrical connection to the catalyst and (b) can be adapted easier to commercial exhaust units.

Deposition of nanoparticles of iridium dioxide on a synthetic boron-doped diamond surface

Abstract: The electrochem. properties of IrO2 nanoparticles deposited on a synthetic boron-doped diamond surface (BDD/IrO2) were investigated. After a description of the prepn. procedure by thermal decompn. technique, the morphol. characterization of the samples by SEM and TEM was discussed. The electrochem. behavior of the redox system 1,4-benzoquinone/hydroquinone (Q/H2Q) was studied on BDD electrodes with a different IrO2 loading. The kinetics parameters such the transfer coeffs. a and b and the reaction rate const. k0 were calcd. Oxygen evolution and oxidn. of org. compds. were investigated on both BDD and BDD/IrO2 electrodes by voltammetric measurements and preparative electrolysis. A phenomenol. model is proposed to explain the behavior of electrodes. [on SciFinder (R)]

Loop-controlled chlorine production for disinfection of poolwater using boron-doped diamond electrodes

Abstract: Diamond coatings of 0.1 to 1 mm thickness on silicon disks, used as electrodes in electrochem. reactors or systems like a DiaCell have shown outstanding properties in oxidn. of org. and inorg. compds. This reactivity can be assocd. with the prodn. of hydroxyl radicals, which may also be responsible for the prodn. of chlorine or ozone in naturally mineralized water. By addn. of a small amt. of supplementary NaCl to poolwater (250 to 900 ppm), it is possible to produce up to 10 g/h of chlorine. With the help of a newly developed online and direct measuring-free chlorine amperometric sensor, the loop-controlled prodn. of chlorine can easily be maintained in the range of 0.2 to 0.4 ppm free chlorine and guarantee the perfect disinfection of the poolwater. The simultaneous prodn. of even more powerful oxidants also helps to destroy incorporated org. materials in swimming pools. [on SciFinder (R)]