Study On CO+NO Reaction Mechanism Of Carbon Material Surface Based On DFT Simulation

Nitrogen oxide(NOx)is a serious atmospheric pollutant.Selective catalytic reduction(SCR)has become the most widely used method of NOx removal.In recent years,researchers have carried out a series of studies around the NO removal performance of carbon materials,and the form of metal-Semi-coke catalyst catalyzed CO reduction of NO has gradually become the mainstream.In addition,our research group previously proposed a rotary reactor,the core of which is to effectively avoid unnecessary catalysts consumption through the adsorption-reduction decoupling method.However,the microscopic reaction mechanism analysis of NO catalyzed by semi-coke is relatively weak.In order to understand the role of NO removal catalyst in the reaction in principle,it is necessary to conduct a comprehensive simulation study on the mechanism of CO reduction of NO on the surface of iron-modified active semi-coke catalyst.In this paper,the effect of iron adsorption at different sites of semi-coke on the NO catalytic reduction efficiency was investigated.Through reaction path analysis,thermodynamic analysis and kinetic analysis,the order of activation energy was Ea L-H-I-2>Ea L-H-I-1>Ea L-H-I-3;Ea L-H-II-2≈Ea L-H-II-1>Ea L-H-II-3.That is,when Fe atoms were adsorbed on the semi-coke surface in bonded form(C-Fel and C-Fe2),the NO catalytic reduction effect was significantly better than that when Fe atoms were adsorbed on the SC surface in non-bonded form(C-Fe3).And the best effect was obtained when Fe was modified on the single vacancy semi-coke(C-Fe2).Subsequently,the microscopic mechanism of iron promoting the NO adsorption on Fe/SC surface was investigated.A control model of Fe/SC and SC was established,and the NO adsorption state on the model surface was investigated by coupling O2.The adsorption configurations of Fe/SC and SC in different NO/O2 adsorption order were calculated,and the similarities and differences in adsorption energy,bond order and charge distribution were compared.It was found that the addition of iron atoms would lead to the obvious electrons transfer to the carbon site.This indicated that the iron in Fe/SC improved the direct adsorption capacity of carbon active sites for NO and O2,and promoted the formation of NO3-and other groups at the iron active site in the case of NO coupled with O2.In order to explore the NO heterogeneous reduction path in CO atmosphere,a zigzag semi-coke model containing both nitrogen and iron was established.The kinetics of NO catalytic reduction was quantitatively analyzed in the range of 300～1000K.Nitrogen doping provided the new active sites for the catalytic process and improved the NO removal rate in low concentration atmosphere.At the molecular level,it was proved that in CO reduction atmosphere,CO would replace the function of FeO group and further reduce the reaction activation energy.That is,the sequence of NO heterogeneous reducing power was CO+Fe>FeO(without CO)>without Fe and CO.Finally,the microscopic mechanism of NO catalytic reduction on Fe/SC surface in a rotating reactor was systematically studied.The adsorption zone and reduction zone were isolated.NO first formed NO2,N2O and NO3-functional groups in the adsorption zone,which would be replaced by CO in the reduction zone.The macro performance was that the NOx content would peak in the middle of the experiment.The simulation also demonstrated that FeO group and high CO concentration could ensure the integrity of Fe/SC surface active sites.In addition,only one step was needed to complete the N2 releas in the reduction zone,which illustrated the convenience of NO reduction by adsorption-reduction decoupling method.In conclusion,some phenomena in denitration experiment were reasonably explained by simulation in this paper,which provided theoretical support for the subsequent research.Moreover,the effectiveness of the adsorption-reduction decoupling method for NO catalytic reduction was verified at the microscopic mechanism level,which provided a new idea for the denitration process design and catalyst preparation in the future.