Heterogeneous Reaction Of NH₃ On Mineral Oxide Surface

In recent years,our country has faced severe regional haze pollution problems.The essence of haze is the atmospheric turbidity caused by the explosive growth of atmospheric fine particle concentration.Secondary inorganic aerosols?sulfate,nitrate,ammonium,etc.?are one of the main sources of fine particulate matter in the atmosphere.Mineral particles are the aerosol particles with the highest flux on land,and their surface is an important place for heterogeneous secondary aerosol formation.NH₃ plays an important role in the formation of secondary aerosols,but the specific reaction mechanism is unclear.Therefore,exploring the heterogeneous reaction process of NH₃ on the surface of mineral oxides is of great significance for exploring the cause of haze.In this paper,the in-situ infrared spectroscopy and flow tube reaction device system were used to study the heterogeneous reaction of NH₃ on the surface of five common mineral oxides under light and dark conditions,and explore the heterogeneous reaction of NH₃ on the surface of TiO₂ when SO₂ coexists The main research results are as follows:?1?Under dark conditions,NH₃ has both physical and chemical uptake on the surface of mineral oxides.The products produced by heterogeneous reactions on the surfaces of different mineral oxides are not exactly the same,but they mainly exist in the form of metal atom coordination NH₃ and Br?nsted acidic sites adsorbed NH₄⁺;under light conditions,the adsorption of NH₃ on the surface of TiO₂ will It is oxidized to NO₃^-and further photolyzed to form NO and NO2.?2?The semi-quantitative analysis of the uptake capacity of NH₃ on the surface of five kinds of mineral oxides shows that acidic oxides TiO₂ and?-Al₂O₃ have a larger uptake capacity for NH₃,basic oxide MgO and low active oxide SiO₂ The NH₃ uptake capacity is relatively small,and the NH₃ uptake capacity per unit mass of oxide is:TiO₂>?-Al₂O₃>Fe₂O₃>SiO₂>MgO.?3?The effects of coexistence of SO₂ on the heterogeneous reaction process of NH₃under the presence or absence of light were studied.It was found that the photoreaction of SO₂ on the surface of TiO₂ mainly produces sulfate;the presence of surface sulfate will promote the formation of Br?nsted acid sites.Under dark reaction conditions,a single NH3 reaction mainly adsorbs at the Lewis acid site to form coordinated NH3,and when it reacts with SO₂,it is converted to NH₄⁺at the Br?nsted acid site,and the amount of adsorption increases;under photoreaction,NH₃photooxidation produces NO₃^-,And further photolysis to generate NOx,the presence of SO₂ will make the dominant species of nitrate in the product change from bidentate nitrate to bridge nitrate,and reduce the amount of NOx produced by NH₃photooxidation products.