Detailed Mechanism On NOx Reduction By H₂ In Automotive Exhaust Gases

At present,there is a great development of the automobile industry.However,the exhaust pollution of automobile has become increasingly serious in the atmosphere.Especially under the conditions of high-temperature and lean-burn combustion much nitrogen oxides is produced.So more and more attentions from goverment and society are paid on automotive exhaust emission.In order to comply with the future stricter emission regulations,there still remains a lot to be done in several fields of automotive exhaust after-treatment system.These aspects vary from practical research on new materials and novel techniques to improve catalyst microstructure,particularly numerical simulation of detailed chemical reaction dyramics is an effective method of optimization of catalytic converters,to theoretical cortributions of detailed descriptions of chemical phenomena inside the converters and proposals of mechanistic reaction schemes.This thesis firstly summarizes the advances and trend of the NOx after-treatment for automotive exhaust emissions.The detailed mechanism of nitrogen oxides reduction by hydrogen on the rhodium surface is investigated by means of plane-wave density functional theory(DFT) calculation from quantum chemistry and unity bond index-quadratic exponential potential(UBI-QEP) method for calculating reaction parameters.CASTEP program of Materials Studio Software has been used to calculate the chemisorption,transition state and activation energy of H₂,NO and the intermediate products N₂O,NH,NH₂,for deducing the detailed mechanism of nitrogen oxides reduction by hydrogen on the rhodium surface step by step.Then the detailed reaction mechanism is coupled with the perfectly stirred reactor model of CHEMKIN code.Finally the simulation results are compared to experimental results from literature under the same conditions and the comparison suggests that kinetic numerical simulation can predict well the exit concentrations of the reaction system.