Mechanism of NOx Reduction by Ethanol on a Silver-Base Catalyst

摘要

Since there is a trade-off relationship between NOx and particulates in exhaust gas emitted from a diesel engine, simultaneous reduction of the amounts of NOx and particulates in a combustion chamber is difficult. However, the amount of particulates produced in the combustion process could be reduced in a state of almost complete combustion, and the amount of NOx produced during the combustion process could be reduced by the use of a catalyst and reducing agent in the exhaust process. It has been demonstrated that the use of ethanol as a reducing agent on a silver-base catalyst in the presence of oxygen is an effective means for reducing NOx, although the mechanism of the reduction has not been elucidated. Therefore, in the present study, an NOx-reduction apparatus was conducted, and model experiments on NOx reduction were carried out in an atmosphere simulating exhaust gas emitted from a diesel engine and at the same catalyst temperature as that in a combustion chamber. The correlations of NOx reduction rate with the amounts of the components produced by ethanol decomposition and the amounts of the components produced by ethanol oxidation were determined with the aim of elucidating the mechanism of NOx reduction. It was found that NOx is reduced when ethanol is oxidized into acetaldehyde and, furthermore, when oxidized or partially oxidized products are formed by acetaldehyde oxidation. It was also found that the NOx reduction rate when ethanol preheating was used was highest (75-95%) at the catalyst temperature of 500 regardless of the ethanol preheating temperature.