Electrochemical Exhaust Gas Purification

This text is divided into two parts; the first part gives a short recapitulation of the development status of the electrochemical reactor for soot removal, while the second part gives a description of activities on electrochemical NOx reduction. The Electrochemical Reactor for filtration and continuous combustion of soot from diesel exhaust gas has been described earlier [1, 2]. The reactor size has been increased by stacking flat plate reactors, and full size test has been performed on a diesel engine in a test bench. The soot removal efficiency is better than 90%, but the efficiency for gas oxidation (conversion of carbon monoxide (CO) and hydrocarbons (CH)) is still low, of the order of 50%. The packing and mounting of the reactor is under development to avoid mechanical breakage by engine vibrations. This has improved the durability significantly, and on road vehicle test is under initiation. Optimisation of reactor shape and materials are going on continuously to improve efficiency and durability. In this phase various production methods are under consideration. Activity to extend the electrochemical principle to lean NOx removal is increasing. In this work a concept for electrochemical removal of NOx under lean conditions is outlined. The main obstacles to the design of an effective and energy efficient electrochemical DeNOx reactor are presented. The use of a selective electrode in combination with the need to be able to control the applied potential and, following from this, the need for a simple geometry of the reactor is stressed. A selective electrode for nitric oxide reduction has been identified.