Density Functional Theory Study On Denitrification Mechanism Of NH₃-SCR On CePO₄/Mn-CePO₄ Crystal Surface

In the current social and human activities,industrial combustion,motor vehicle exhaust,and certain chemical production processes generate a large amount of NOx,which damages social and economic development and ecosystems,and seriously affects human health.At present,selective catalytic reduction technology（NH₃-SCR）is the most effective method to remove NOx.In order to explore the denitration process and denitration mechanism of NH₃-SCR on the surface of Ce PO₄ and metal-doped Ce PO₄,density functional theory and VASP software were used in this thesis.Using cerium phosphate as the substrate and metal manganese as the doping metal,the adsorption behavior and reaction mechanism of the reactant NH₃/NOx on the surface of the cerium phosphate crystal were studied.The initial calculation model was built by software,and the adsorption of NH₃/NOx molecules was carried out after selecting the optimal crystal plane.The adsorption characteristics of NH₃/NOx on Ce PO₄ and Mn-doped Ce PO₄ surfaces were analyzed,and the effect of Mn doping on the crystal plane structure of Ce PO₄ was investigated,and compare the adsorption energy,charge density,density of states,and charge change.The final result is that the NH₃-SCR reaction in the Ce PO₄ system has both the L-H mechanism and the E-R mechanism,and the NH₃-SCR reaction in the Mn-Ce PO₄system is dominated by the E-R mechanism.At the same time,the following conclusions are drawn:（1）The（010）crystal plane is the most stable crystal plane of Ce PO₄ crystal,and the exposed atoms at the terminal end are oxygen atoms.Monoclinic monazite Ce PO₄ has a layered structure,and there are unsaturated coordination metal atoms and oxygen atoms on the surface.In the Wulff structure,the（001）,（010）and（100）planes account for 14%,45%and 41%of the total area,respectively.（2）There are both Br?nsted acid sites and Lewis acid sites on the surface of Ce PO₄,both of which can adsorb NH₃ molecules.B acid can be formed by the mineral itself OH-ion,and can also be formed by the transformation of L acid.NO molecules are adsorbed on Ce atoms and filled O’atoms,NO₂ is adsorbed on Ce atoms,and Ce-OH can adsorb both NH₃ and NO molecules.The adsorption capacity of NH₃ on P=O-H is the strongest,the adsorption capacity of NO on Ce-OH is the strongest,and the adsorption capacity of NOx on the surface of Ce PO₄ is weaker than that of NH₃.There is a competitive adsorption of NOx and NH₃ on Ce top.（3）NH₃ in the Mn-Ce PO₄ system is more easily adsorbed on the L acid site and easier to decompose.The B acid site has poor selectivity to NH₃,and the B acids in the oxygen vacancy system can be converted to each other.Both Ce atoms and O atoms on the surface can adsorb NO molecules,and the O’atoms after filling the oxygen vacancies can also adsorb NO molecules.Ce-OH can adsorb both NH₃ and NO molecules,which are oxidized to-ONOH species.The adsorption capacity of NH₃/NO molecules on the surface filled with oxygen vacancies is stronger.NO₂ cannot be adsorbed on Ce top and Mn top sites.（4）After the Ce PO₄ surface was doped with Mn atoms,the structural stability of the surface became worse,and the surface geometry changed.The surface O atoms in the Mn-Ce PO₄ system are unstable and their chemical binding ability is reduced.The doping of Mn atoms can promote the formation of oxygen vacancies on the surface of cerium phosphate.