Theoretical Study On The Heterogeneous Transformation Of Typical Nitrogenous Compounds

Nitrogen compounds are an important type of environmental pollutants,which not only cause serious harm to the environment,but also directly or indirectly threaten human health.Titanium dioxide and its modified materials,as excellent catalysts,can convert green and sustainable light energy into chemical energy needed to degrade pollutants.Therefore,they are widely used in pollutant treatment and enviroumental self-cleaning.Such catalysts can be used as environmental self-cleaning materials and environmental remediation materials to participate in the conversion and removal of nitrogen-containing compounds in the environment.Therefore,it is of great significance to explore the conversion mechanism of typical nitrogen-containing pollutants on titanium dioxide catalyst for assessing the harm to the environment.In this dissertation,the theoretical calculation method is used to study the structural properties and reaction mechanism of inorganic nitrogen-containing compounds(NO₂ and NO)and typical organic nitrogen-containing compounds(C₆H₅NH₂)on the TiO₂ and its modified materials at the micro level.1.the reaction mechanism are explored that titanium dioxide as a self-cleaning material promotes the oxidation of SO₂ by NO₂ in the atmosphere and the influencing factors of the reaction.2.the degradation mechanism of NO and aniline catalytic oxidation promoted by these catalysts as environmental remediation materials is investigated.The research results obtained as follows:1.The reaction mechanism of NO₂ oxidizing SO₂ and the influence of H₂O,NH₃,pure particle surface(TiO₂),and TiO₂ surface that adsorbs important atmospheric components(H₂O,NH₃ and SO₄^2-)on the converdion of SO₂ and NO₂During the period of haze,with the increase of aerosol particles and NO₂ content,the content of sulfate increases.NO₂ acts as an oxidant to promote the oxidation of SO₂,which may be a key missing pathway for the source of sulfate in the atmosphere.In this chapter,theoretical calculation method is used to study the reaction mechanism of SO₂ and NO₂ and the formation of intermediate N₂O₄.In addition,the effects of H₂O,NH₃,pure particle surface(TiO₂)and particle surface containing other atmospheric components(H₂O,NH₃ and SO₄^2-)on the conversion of SO₂ and NO₂ to sulfate are also analyzed.The results show that SO₂ can be oxidized to SO₃ by the intermediate N₂O₄,while N₂O₄ can be reduced to HONO.And the oxidation process is the rate-determining step of the whole reaction.In the homogeneous reaction,H₂O molecules participate in the atmosphere to reduce the energy barrier of the oxidation processes and promote the generation of HONO.With the increase of the number of H₂O molecules in the system,the energy barrier of the oxidation processes decreases correspondingly.NH₃ has a more significant stabilizing effect on the product complex than H₂O.And,H₂O and NH₃ can promote the oxidation of SO₂ and NO₂ in thermodynamics,however,there can not significantly promote the catalytic oxidation reaction of NO₂ and SO₂.The results of heterogeneous reaction show that the effect of pure particle surface(TiO₂)on the oxidation of SO₂ to sulfate by N₂O₄ is not significant.However,when the particles surface contains different amounts of H₂O,NH₃ and SO₄^2-,they can effectively reduce the energy barrier of the oxidation step.When one NH₃ molecule and one H₂O molecule are adsorbed on the TiO₂(101)surface,SO₂ is easily oxidized by cis-ONONO₂.The reaction energy barrier is 4.54 kcal mol^-1.When more H₂O molecules are adsorbed on the surface,SO₂ will first occur hydrolysis reaction to form HSO₃^-.However,HSO₃^-is more difficult to be further oxidized to sulfate by asy-ONONO₂ than SO₂.The study gains more insight into the contribution of SO₂ and NO₂ to haze and the potential impact of atmospheric constituents(including H₂O,NH₃,H₂O/NH₃/TiO₂ and SO₄^2-/TiO₂)on the formation sulfate.The results provide a theoretical basis for the transformation of NO₂ in atmospheric environment.2.Study on the selective catalytic oxidation mechanism of NO to HNO₃ on TiO₂(101)and(001)surfaces and the formation mechanism of intermediate N₂O₄ and HONOControlling NO emission is an effective measure to reduce NO₂ content in atmosphere.Theoretical study on the selective catalytic oxidation of NO to form HNO₃ on the different TiO₂(001)and(101)surfaces is performed by DFT calculations.The effect of additional NO molecules on the formation of intermediates HONO and N₂O₄ also is discussed.The result shows that,in the absence of light,HNO₃ can also be more easy to generate on(001)than(101)surface.The adsorbed H atom on surface is beneficial for the transformation of O₂ to the superoxide radical(O₂^-)that has a favorable role for the oxidation of NO on surface.In addition,it is manifestly demonstrated that the participation of the additional NO in the reaction of NO and O₂ not only modifies the known NO oxidation pathway(NO?NO₂?HNO₃),but also affects the existence of the product HNO₃.The trans-ONONO₂ can firstly be formed if the additional NO molecule involves in the oxidation reaction in the beginning.When the additional NO molecule encounter with the precursor(H…NO3)of oxidation product(HNO₃),it can improve the formation of HONO not HNO₃.This study gains more insight into the mechanism of NO oxidation and has a potential atmospheric importance.3.The calculation of the structural properties of the MgO/TiO₂ composite catalyst and the study of the catalytic oxidation mechanism of aniline at different reaction sites(MgO and TiO₂)MgO/TiO₂ has been developed into an efficient catalyst to remove aniline organics that are difficult to degrade,highly toxic and have strong environmental persistence.density functional theory(DFT)method is used to study the degradation mechanism aniline on MgO/TiO₂ composite catalyst.(MgO)₃ clusters are stably supported on TiO₂ catalyst by chemisorption(Eint=181.67 kcal mol^-1),and the MgO/TiO₂ composite catalyst formed by this method has high catalytic activit.The enhanced photocatalytic activity is beneficial for the formation of surface oxidation radical superoxide radical(O₂^·-).When AN-structures are stably adsorbed on different sites(MgO and TiO₂)over MgO/TiO₂ composite catalyst(?-2 and ?-3),the non-radical pathway by O-surface initiation is a priority to take place at MgO-site,and the radical pathway preferentially occurs at TiO₂^- site by O₂^·-.It is found that these reactive-sites including active O atoms and oxygen vacancies are located on MgO-clusters of the MgO/TiO₂,and are mainly responsible for subsequent catalytic-oxidation(dehydrogenation and oxygenation)of AN.This study has further understood on the reaction mechanism of aniline catalytic oxidation(including non-free radical and free radical process).It is certain significance for the design and optimization of the catalysts that degradation of aniline and other similar environmental pollutants.