Preparation Of V₂O₅/TiO₂-Graphene Catalyst And Study On Its Denitrification Performance At Low-Temperature

With the rapid development of the economy,the problem of air pollution has become a global environmental issue.Among them,as one of the main components of air pollution of nitrogen oxides?NO_x?are more serious to the environment.Selective catalytic reduction?SCR?technology is considered to be the most effective way to treat NO_x.Vanadium-titanium-based catalysts are the key of SCR and have good denitration efficiency and high resistance to water and sulfur poisoning.However,its high operating temperature and narrow temperature window make it difficult to adapt to the low load operation of industrial boilers and NO_x emission control of non-electrical industry with low exhaust gas temperature.Therefore,it is urgent to develop a denitration catalyst having a low operating temperature and a wide temperature window.In this paper,graphene with large specific surface area and high electron mobility was introduced into vanadium-titanium denitration catalyst and used to improve the redox of the catalyst.And the influence of graphene content on the structure,physicochemical properties and catalytic activity of the catalyst were systematically studied.The structure-activity relationship of the catalyst was established,and the low-temperature catalytic mechanism was elucidated.The catalyst with low temperature and wide temperature window was obtained.The main research work and results of this thesis are as follows:1.The composite mechanism of V₂O₅/TiO₂-graphene catalyst was studied.V₂O₅/TiO₂-graphene catalyst with uniform particle size and uniform dispersion was prepared by stepwise method.The effects of the introduction of graphene on the phase parameters,specific surface area and elemental chemical state of the product during the synthesis were analyzed by XRD,BET and XPS.To clarify the composite process between graphene,V₂O₅ and TiO₂,it was found that there was a strong interaction between them,which was beneficial to the electron transport on the catalyst surface.2.The structure-activity relationship of V₂O₅/TiO₂-graphene low temperature denitration catalyst was studied.The effect of different graphene content on denitration activity was systematically studied.When the graphene content was 0.2wt%,the denitration efficiency was more than 77%at a temperature greater than180°C.At 240°C,the NO_x denitrification efficiency reached 100%,which showed good low temperature catalytic activity and wide temperature window and had good water and sulfur resistance.The relationship between the structure-physical property and catalytic activity of the catalyst was established.It was found that the introduction of graphene produced more surface chemisorbed oxygen and low-valent vanadium oxide,which were the key factor for the low temperature activity of the catalyst.3.The mechanism of low temperature denitration of V₂O₅/TiO₂-graphene catalyst was studied.The in situ Diffuse Reflectance Fourier Transform Infrared Spectroscopy?in situ DRIFTS?was used to analyze the adsorption and desorption behavior of NO_x and NH₃ on the catalyst surface,and to explore the key active substances and SCR reaction pathways on the catalyst surface.The analysis found that the SCR reaction on the catalyst surface conformed to the Eley-Rideal mechanism and the Langmuir-Hinshelwood mechanism.The introduction of graphene provided abundant active oxygen species and acid sites.NO formed NO₂ on the catalyst surface,and NO₂ could promote the rapid SCR reaction,thus improved the low temperature activity of the catalyst.