The influence of NOx on the oxidation of metal activated diesel soot

The influence of NO on the oxidation of metal (cerium, copper, and iron)-ac tivated soot was studied. Without NO in the gas phase, the activation energ y of soot is approximate to 170 kJ/mol, independent of the type of metal ap plied in the soot. The rate-limiting step in the oxidation with oxygen is p robably the decomposition of surface oxygen complexes. in presence of NO, t he oxidation rate of soot mixed with a supported platinum catalyst is incre ased significantly, especially for cerium-activated soot. The activation en ergy of the oxidation reaction is decreased by the presence of NO in the ga s phase. The increase in reaction rate as a result of NO and a platinum cat alyst is explained by a cycle of two catalytic reactions, where platinum ox idises NO to NO2, which subsequently oxidises soot using cerium as a cataly st, forming NO which can participate in the reaction more than once. This o xidation mechanism can be put into practice by combining a platinum-activat ed particulate trap with a combination of platinum and cerium fuel additive s. This combination might be a breakthrough in the search for an applicable catalytic soot removal system. (C) 1999 Elsevier Science B.V. All rights r eserved.