Adsorption Behavior Of Elemental Mercury And Ammonia On Typical Catalysts Surfaces By The DFT Method

The elemental mercury（Hg⁰）and ammonia（NH₃）,as two important air pollutants,are of great significance for their stable structures and chemically indifferent property.Environmental Protection Agency（EPA）of the U.S labeled the former one as one of priority pollutants since its bioaccumulation and neurotoxicity.The latter one contributed to the formation of haze in the presence of sulfuric acid and nitric acid.Since a large number of experimental studies on Hg⁰ adsorption behavior and related mechanisms are not clear,the investigation of Hg⁰ inteation mechanisms on the surface for the design of good performance Hg⁰ sorbents/catalysts is essential.NH₃,contributing the formation of PM2.5 in haze,will be one of the key pollutants in the future air pollution control.Hence,the development of high efficiciency NH₃adsorption and catalytical materials should be in our agenda.Density functional theory（DFT）calculations provide an economic efficient method to study the adsorption behavior and to predict the interfacial processes and mechanisms of related materials,which is of great significance in the development of adsorbents and catalysts.In this study,DFT method has been employed to study the adsorption behavior and mechanisms of Hg⁰ and NH₃ molecules on the adsorbent surfaces at an atomic level by the DMol3 module in Materials Studio 7.0.The main contents and conclusions of this thesis are as follows:（1）The typical metal chloride MnCl₂ and metal oxide Co₃O₄ were selected as sorbents for Hg⁰ adsorption.In addition,CoMnO₃,a doule-metal oxide,was taken into consideration for the investigation of Hg⁰ control.The adsorption of Hg⁰ on MnCl₂（11 0）and Co₃O₄（1 1 0）surfaces were chemical interaction with adsorption energies of156.620kJ/mol and 74.037kJ/mol,respectively.The s orbital of Hg⁰ hybridized with p orbital of Cl atom and the s and d orbital of Hg⁰ interact with d orbitals of Mn.The s and p orbitals of Co³⁺had strong interaction with s and d orbitals of Hg⁰.The adsorption equilibrium constant ln(K_eq)negatively correlated with the temperature,and the Co₃O₄surface exhibited stronger temperature tolerance than MnCl₂.The adsorption of Hg⁰ on CoMnO₃ low index surfaces was also chemical adsorption.The CoMnO₃（1 0 0）surface affinity of Hg⁰ was the strongest with the highest adsorption energy.Moreover,the adsorption energy positively correlated with the electron transfer in each system.（2）C60 and fullerene TiO₂,two important spherical materials,are essential for the improvement of ball structrure sorbents/catalysts design and performance.The metal active center（M）of C60 was constructed by in situ substitution method.The adsorption behavior of Hg⁰-C59M was systematically studied.C59M can effectively reduced the E_gap compared to C60.The results indicated that most of C59M materials had physical interation with Hg⁰.Hg⁰ adsorption on C59Zn,C59Mn,C59Fe,C59Co and C59Ni were chemical adsorption.Those high active adsorption transition metals distributed in VIII,VIIB,VIB and IIB in the periodic table of elements.Besides,Hg⁰ and NH₃ molecules were chemically adsorbed on the fullerene TiO2 cluster with the adsorption energy of506.196kJ/mol and 1261.597kJ/mol,respectively.The Ti-O_term（O）was very active for Hg⁰ and NH₃ adsorption.In terms of PDOS analysis,the d orbitals of Hg⁰ and the p and d orbitals of NH₃-N interacted with p,d orbital of O atom in fullerene TiO2.The co-adsorption energy of Hg⁰ and NH₃ molecules on the surface of fullerene TiO2 is504.726kJ/mol,which indicated that the adsorption energy of NH₃ molecule was greatly reduced.（3）The adsorption of NH₃ was chemically adsorbed on ZnFe₂O₄（1 1 0）surface by DFT calculations.Suface Fe³⁺and Zn²⁺were investigated as active sites.The adsorption energy of H₃N-Fe and H₃N-Zn were 173.738kJ/mol and 203.125kJ/mol,respectively.The activation of NH₃ on Zn²⁺site is stronger than that on Fe³⁺site.The p orbitals of NH₃ hybridized with Zn p orbitals.Compared with NH₃ adsorption on fullerene TiO₂,the activation of NH₃ on the curved surface was more obvious than that on the surface of the flat surfaces.（4）The Quantitative Structure-Activity Relationship（QSAR）model of adsorption energies and adsorption-related parameters of Hg⁰ on C59M clusters was constructed.Ninteen kinds of clusters and twenty geometric and electronic structure descriptors were selected to establish the model by multiple linear regression method.The results showed that the adsorption energies correlated with L_Hg-M,E_gapap and E_HOMO,and the optimal model was recommended as the E_ads（p）=152.467-33.556L_Hg-M-13.92E_gap.The prediction performance of the model is robust,which can be used to predict the adsorption of Hg⁰ on C59M material surfaces.Low E_gap materials were more favorable on Hg⁰ adsorption.These findings may shed new light on research of Hg⁰ adsorption materials.