Estimation of the Coverages of the Surface Intermediate Species Formed During the Reduction of NO_x Emissions on Supported Rh Catalysts


Abstract: Reduction of NO by CO is one of the most important reactions that take place in catalytic converters, during the purification of exhaust gas of motor vehicles. Despite the fact that this reaction has been widely studied, the reported reaction orders and the activation energies differ depending on the experimental conditions. The aim of this study was to analyze the reaction model by implementing micro-kinetic analysis in order to explain the differences between the reported reaction orders and activation energies in the literature. In this study, a {\it dissociative mechanism} was proposed for the reduction of NO by CO over Rh/SiO$_2$ catalyst, and kinetic parameters belonging to each of the steps present in the proposed mechanism, were extracted from the experimental/theoretical studies in the literature. The assumptions made for the model were based on the experimental results in the literature and a computer program was written that is able to calculate the reaction rate, reaction orders and the coverage of surface species. The results of the computer program indicated that the surface of the catalyst was covered by the CO molecules over a low temperature range and by the oxygen atoms over a high temperature range. It was observed that this change could affect the activation energy and the reaction orders.

Keywords: Reduction with CO, NO$_x$ Reduction, NO$_x$ Emissions, Catalytic Converters.

Full Text: PDF