Mechanism Study On The Catalytic Performance Of ZSM-5 Supported Mn/Co-Al/Ce/Ti Catalysts For SCR And Fast-SCR

Nowadays,the problem of environmental pollution in China is becoming more and more serious.NO_x is one of the major pollutants that endanger the atmosphere and is the main cause of smog.NO_x emission control is a common concern,so it is urgently needed to deal with NO_x.SCR?Selective Catalytic Reduction?is one of the effective methods to remove NO_x from fixed sources.SCR technology uses NH₃ as the reductant?NH₃-SCR?,which can make the NO_x removal rate reach more than 85% under the action of the catalyst.The research shows that during the SCR reaction,it is more efficient to properly increase the proportion of NO₂ in NO_x than NO alone.Therefore,the Fast-SCR technology has been developed.Therefore,based on the important role of SCR reaction in the field of denitrification,this paper uses quantum chemistry to study its catalytic mechanism in more detail.In this paper,the quantum chemical density functional theory is used to calculate the reaction mechanism of SCR and Fast-SCR.Based on the Eley-Rideal mechanism?ER mechanism?,the reaction between Fast-SCR and SCR is basically similar.SCR is a reaction of NO with NH₃ supported on a catalyst and then NH₂ and HNO are generated,and then NO reacts with NH₂ supported on a catalyst to produce products N₂ and H₂O.However,Fast-SCR is slightly different.The biggest difference between the two is that under the action of the catalyst,SCR utilizes the reaction of NO and ZSM5-NH3 to generate ZSM5-NH₂,while the rapid SCR utilizes the reaction of NO₂and ZSM5-NH₃ to obtain ZSM5-NH₂.Through the ab initio calculation method in quantum chemistry,the reaction mechanism of SCR and Fast-SCR of transition metal Mn and Co on molecular sieve ZSM-5 has been studied.The reaction process of SCR and Fast-SCR has been determined.And the reactants,transition states,intermediates and products involved in the reaction are optimized and their zero energy is obtained.Then,the reaction energy barrier of each step of the reaction process is calculated.Finally,the activation energy of the entire reaction is obtained.The comparison between the calculation results of the SCR and the rapid SCR reaction is discussed,and the reaction mechanism of the rapid SCR is discussed.Calculations show that:In the case of Si as ZSM5-Mn or ZSM5-Co attachment center,the Fast-SCR reaction has a lower energy barrier?83-88 kJ/mol?compared to the SCR reaction?155-220 kJ/mol?.It shows that Fast-SCR has obvious catalytic effect,which also reveals the catalytic mechanism of SCR and Fast-SCR.The catalytic effect of ZSM5-Mn?107-155kJ/mol?is better than that of ZSM5-Co?154-220kJ/mol?for the SCR reaction.Similarly,for the fast SCR,ZSM5-Mn?40-84kJ/mol?is better than that of ZSM5-Co?61-88 kJ/mol?.This may be due to the fact that Mn has more chemical valence and better redox catalysis.Due to the chemical inertness of Si,it is possible to further reduce the energy barrier of SCR and Fast-SCR reaction by changing the attachment centers of the catalysts by doping Al,Ce and Ti metals.The energy barrier of SCR reaction is reduced from 150-220kJ/mol to 100-170kJ/mol,and the energy barrier of Fast-SCR reaction is reduced from83-88kJ/mol to 40-72kJ/mol,which improves the catalytic effect significantly.This shows that the SCR and Fast-SCR catalysts are not only related to the surface transition metal?Mn/Co?but also highly related to the catalytic attachment center?Al/Ce/Ti?,which also provides some theoretical references for the subsequent research and development of SCR and Fast-SCR catalysts.