Advance in Nanostructural Electrochemical Reactors for NO X Treatment in the Presence of Oxygen.
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Advance in Nanostructural Electrochemical Reactors for NOX Treatment in the Presence of Oxygen. Koichi HAMAMOTO*1, Yoshinobu FUJISHIRO1, Masanobu AWANO1, Shingo KATAYAMA2 and Sergei BREDIKHIN3 1 Advanced Manufacturing Research Institute, AIST, Shimo-Shidami, Moriyama-ku, Nagoya 463-8687, Japan 2 Synergy Ceramics Laboratory, FCRA, Shimo-Shidami, Moriyama-ku, Nagoya 463-8687, Japan 3 Institute of Solid State Physics Russian Academy of Science, 142432 Chernogolovka, Russia ABSTRACT Dramatic improvement in the selective separation and purification of NOX in exhaust gases by an electrochemical reactor with a catalytic electrode has been achieved. The novel electrochemical cells for NOX decomposition were developed by nano-scale control of penetrating pores from the catalytic electrode surface to the bottom of the catalytic electrode layer. The penetration pores and nano-size Ni grains are self-assembled at NiO/YSZ interfaces in the catalytic electrode by oxidization-reduction reaction of the NiO during the cell operation. In order to use reduced Ni for NOX decomposition reaction efficiently, we successfully designed a functional multilayer catalytic electrode. By multilayering of the catalytic electrode, adsorption and decomposition of coexisting oxygen in exhaust gases was suppressed and the selectivity of NOX decomposition reaction is improved. Structural change of the catalytic electrode as a result of the electrochemical processes was investigated and correlated with the NO decomposition properties of the cell. INTRODUCTION The reduction of Nitrogen oxides (NOX) emission from vehicles has become one of the greatest challenges in environment protection. Air pollution by NOX in combustion waste causes serious environmental problems in urban areas, especially [1,2]. Without coexisting oxygen the successful decomposition of NO gas into oxygen and nitrogen was demonstrated over 30 years ago by the development of the “three way catalyst” and other effective catalysts. However, in the presence of excess oxygen, such as lean-burn conditions, three way catalysts do not provide sufficient NOX decomposition. The widely used catalytic decomposition of NOX requires an additional 2-3% of fuel as a reducing reagent, and as a result an increase in the amount of fuel used by the engine. The high efficiency of diesel engines is expected to realise savings in energy consumption even when the exhaust gas includes high partial pressure of oxygen reaching to 10%. This is one reason for the emphasis on the development of high performance catalytic and other systems workable at high PO2 conditions. Environmental solutions must also be accompanied by energy saving technologies. On this view point, the reduction of NOX emissions can be achieved not only by catalytic NOX decomposition but also by electrochemical decomposition. Without coexisting oxygen the successful decomposition of NO gas into oxygen and nitrogen in a primitive electrochemical cell was first demonstrated by Huggins et al [3,4]. They showed that by applying an electri
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