Detailed Mechanism On NOx Reduction By CO In Automotive Exhaust Gases

With the development of auto industry, which makes people's live more convenient, exhaust is becoming one of the most important sources of air pollution. In particular, the harm to environment and human health form NOx can not be ignored. Now NOx removal has been the focus of the world. Three-way catalytic converter is the most commonly used mean for reducing emissions, in which Three-way catalyst (TWC) is the most important part. Noble metal is becoming the main catalyst of three-way catalytic converter for its high activity, high selectivity, high stability and good physical properties, which directly determines the effect of exhaust decontaminating. Detailed numerical simulation of chemical reaction dynamics is a convenient and efficient way to simulate detailed chemical reaction process in the converter, which is the basis to raise the conversion efficiency.In this thesis, it's introduced that the current ways in controlling NOx in exhaust and the development and application of the three-way catalytic converter. Surface reaction mechanism of NOx reduction by CO on noble metal supported catalyst is developed, according to heterogeneous micro-kinetic method. In addition, preexponential factors are calculated by transition state theory and activation energy is calculated by the Unity Bond Index-Quadratic Exponential Potential (UBI-QEP) semi-empirical method. CHEMKIN software is applied in numerical simulation to investigate the species concentration and coverage at different temperatures, which is compared with the data from the experiments, in order to analyze the characteristics of noble metal catalysts and the nature of NOx reduction, as well as the efficiency of catalytic converter conversion. To investigate the importance of the N₂O as an intermediate species during the reduction of NO by CO occurring on TWC, we simulated in three reactors with different sizes and different space velocities. With analyzing the simulation and the experiments results, it is concluded that N₂O is an important intermediate species and N2O+CO reaction is an important intermediate reaction step.