Quantum Chemistry Study Of Catalytic Mechanism On Three Way Catalyst For Automotive Exhaust

In recent years,Chinese economic development is rapid,and car possession of Chinese is increasing,which caused the problem of air pollution is also growing.Automobile exhaust contains a variety of harmful substances,which content higher is CH,CO and NO.The more commonly used automobile exhaust treatment technology can be summarized into three categories: the engine internal purification technology,the engine external purification technology,fuel improvement and replacement technology.At present,the most commonly used is three way catalyst for automotive exhaust,which is one of the engine external purification technology.The key element of this technology is the choice of catalyst,and at present,the study on three-way catalytic technology of the automobile is mainly experimented,and there is no definite conclusion about the specific mechanism of the reaction.First of all,on the basis of quantum chemistry's DFT(Density Functional Theory),different methods and bases were used in this paper to optimize molecule's configuration and calculate the scf energy of the reaction of CH and CO to reduce NO directly.The reaction path and reaction activation energy of the direct reaction are obtained and used as reference for the catalytic reduction reaction.As a result,a possible pathway was gained.Meanwhile,the effect of different optimization and energy calculation methods was analyzed,which made it reliable to compare with the results of catalytic reduction.Then the reactants,transition states,intermediates and products along all the relevant reactions of NO reduction catalyzed by ZSM5 supported transitional metal(Mn)with different attachment site atom(Si,Al,Ce)were calculated and optimized by UB3LYP//SDD method.Possible pathway and activation energy were obtained.Finally,by analyzing and summarizing,the mechanism of these reactions were studied in detail.The results show that there are several reaction paths for the direct reduction of NO reduced by CH and CO,the activation energy for direct reaction of CH and NO reduction is about 150-180 kJ / mol,and the activation energy for the reaction of NO reduced CO is about 290-350 kJ / mol.The results show that the activation energy of NO reduction is much lower than that of CO,and the reduction of CH is stronger than that of CO.The reaction activation energy of NO reduction is about 60-130 kJ / mol in the presence of ZSM5-Mn catalyst,and the reaction activation energy of NO reduction in the presence of catalyst is 120-220 kJ / mol.Therefore,ZSM5-Mn has obvious catalytic effect.In the mean time,different activation energy was obtained when the attachment site atom was different.The catalyst with Al as the catalyst for the deposition of the central atom has a good catalytic effect on both reactions,which indirectly reflects the relatively good catalytic activity of Al2O3 as carrier.It is inferred from the literature that temperature,gas space velocity and carrier will influence the catalytic effect.Therefore,more factors need to be considered in further research.The catalytic mechanism of automotive exhaust catalyzed by ZSM5-Mn was revealed in this paper by using quantum chemistry theory,which could supply a theoretical reference for the further research of three way catalyst for automotive exhaust.