Detailed Mechanism For Catalytic Reduction Of Nitrogen Oxides In Automotive Exhaust Gases

Three way catalysts (TWCs), which are used in the conventional gasoline engines, are not effective in reduction of NOx under lean conditions because of high concentration of O2 in the exhaust. NOx storage and reduction (NSR) and selective catalytic reduction (SCR) are widely concerned due to high efficiency in controlling NOx emissions for lean burn engines. The mechanism of NOx reduction in the automotive catalytic converters is controversial although many experimental studies have been carried out. Rh is widely used as the automotive exhaust catalyst for the outstanding activity and high ability to promote the reduction of NOx. Detailed mechanism for catalytic reduction of nitrogen oxides by carbon monoxide over Rh/Al2O3 catalyst was studied in this thesis.Detailed mechanism of CO-O2 reaction over Rh/Al2O3 catalyst was developed firstly since the oxidation of CO is an important process of CO-NO reaction. Furthermore, CO-NO reaction mechanism was proposed considering the role of N2O during the reduction of NO into N2. Perfectly Stirred Reactor (PSR) model was used to simulate the two global reactions. Simulation results show that detailed mechanisms proposed well predict the effect of temperature on gas species conversion; N2O is an important intermediate species in CO-NO reaction, and N2 produced during the reduction of NO is mainly via CO-N2O reaction as the temperature is lower than 600 K. Plug-flow Reactor (PFR) was used to simulate the reduction process of N2O by CO under three different CO/N2O ratios. Simulation results are in good agreement with experimental data in the literature; the conversion of N2O into N2 does not take place continuously in the absence of CO; the reaction rate of N2O reduction is inhibited by the CO under steady state conditions. Furthermore, sensitivity analysis of species and the effect of kinetic parameters on the simulation results were also studied in this thesis.