Electrochemical promotion of conventional and bipolar reactor configurations for NO reduction

The redn. of NO by CO or C3H6 in the presence of O2, a reaction of great technol. importance, was studied on porous polycryst. 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 2 Au films deposited on the outer side of the tubes were used to polarize the Rh catalyst surface. The exptl. conditions used in this study were close to those in the exhaust of a lean burn or diesel engine, i.e., high flow rates and space velocities and in some cases, considerable excess of oxygen. 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, L, in the order of 100, manifesting the effect of Electrochem. Promotion or Non-faradaic Electrochem. 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 exhibit higher catalytic activity than the unpromoted films, with a considerable decrease in their light-off temp. The effect of Electrochem. Promotion was then studied on these, already Na-promoted Rh catalysts. The effect of Chem. and Electrochem. 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 elec. connection to the catalyst and (b) can be adapted easier to com. exhaust units. [on SciFinder (R)

Electrochemical promotion of an oxidation reaction using a proton conductor

A proton conductor, Ba3Ca1.18Nb1.82O9-alpha, has been used to electrochemically promote, via potential-controlled spillover of protons, a Pt catalyst-electrode for the model reaction of ethene oxidation at temperature 250-350 degreesC. The rate enhancement is up to 12 times that of the open-circuit rate and typically 10(3) times larger than the rate of proton supply to the catalyst. At the highest temperatures and most oxidizing conditions employed an up to threefold permanent electrochemical enhancement in catalytic rate was also observed. In situ a.c. impedance spectra reveal a buildup of sacrificial promoter, most likely OH formed by reaction of spillover protons with chemisorbed oxygen, under electrochemical promotion conditions. The observed pronounced electrophilic (partial derivativer/partial derivativeU less than or equal to 0) behavior, in conjunction with the reaction kinetics, is in good agreement with the recently established rules of electrochemical and classical promotion. (C) 2003 Elsevier Ltd. All rights reserved

Characterization of the reaction environment in a filter-press redox flow reactor

The characteristics of a divided, industrial scale electrochemical reactor with five bipolar electrodes (each having a projected area of 0.72 m2) were examined in terms of mass transport, pressure drop and flow dispersion. Global mass transport data were obtained by monitoring the (first order) concentration decay of dissolved bromine (which was generated in situ by constant current electrolysis of a 1 mol dm?3 NaBr(aq)). The global mass transport properties have been compared with those reported in the literature for other electrochemical reactors. The pressure drop over the reactor was calculated as a function of the mean electrolyte flow velocity and flow dispersion experiments showed the existence of slow and fast phases, two-phase flow being observed at lower velocities