Influence Mechanism Of Support Structure On Catalytic Performance For NH₃-SCR Reaction

The emission of nitrogen oxides（NO and NO₂）from coal fired power plants and automobiles is a serious concern due to their contribution to haze,photochemical smog and acid rain.The selective catalytic reduction of NO_x with NH3 has been proved to be a mature technology for the removal of NO_x.At present,metal oxides such as TiO₂,Al₂O₃ and SiO₂ are usually used as support material for SCR catalysts,which carry active components including Pt,Pd,Ce,V and W on the surface to achieve high activity of SCR.However,Pt and Pd not only belong to precious metals with high costs,but also can result in the non-selective oxidation of NH₃ at high temperatures.Therefore,there are few applications in industry.Thus,non-precious metals Ce,V and W are widely used for the doping of active components.Accordingly,the research on the carrier and the active component has extremely important research significance.In this dissertation,by adjusting the loading order of the active components of the catalyst,the low-temperature activity of the denitration catalyst is improved,the carrier synthesis conditions are used to control the shape of the support,and the active component is loaded to further increase the activity of the denitration catalyst.Basis on this,using SEM,XRD,BET,TEM,H₂-TPR,NH₃-TPD,XPS,Raman and FTIR characterization techniques to study the effect of load sequence on the valence state of the active site of the catalyst,the effect of the carrier shape on the activity of the catalyst and the effect of flower like on the activity of the catalyst.This article mainly carried out the following work:（1）Hydrothermal method and impregnation method are used to synthesize different denitration catalysts by adjusting the order of the catalyst active components V and W.Through a series of characterization analysis,the different active component loading order is related to the valence state of the catalyst active center.The proportion has a further impact and further studied its effect on the catalytic activity.The results show that the V₂O₅/WO₃-TiO₂ catalyst prepared by impregnation with active component V has the best catalytic activity for denitrification.The V₂O₅/WO₃-TiO₂ catalyst has a high atomic ratio of V⁴⁺/(V⁵⁺+V⁴⁺+V³⁺),which increases the acid sites of the catalyst.The increase of acid sites can reduce the apparent activation energy of the catalyst and ensure the mutual transformation of V⁴⁺(V³⁺)and V⁵⁺,and then promote the reaction process of NH₃-SCR through the E-R mechanism to increase the catalytic activity.（2）The hydrothermal method was used to prepare a TiO₂ carrier with a flower-like structure by adjusting the hydrothermal synthesis temperature and synthesis time.Subsequently,the active components Ce and W are loaded on a TiO₂ carrier by impregnation method to investigate the hydrothermal synthesis temperature.The effect of hydrothermal synthesis time on the shape of support TiO₂,and the influence of the shape of the support on the catalyst activity after loading active component are investaged.Under the premise of controlling the hydrothermal synthesis time and adjusting the hydrothermal synthesis temperature,the catalyst has the best activity at 120 °C.At this time,the catalyst presents a rod-like structure.Under the premise of controlling the hydrothermal synthesis temperature and adjusting hydrothermal synthesis time,the catalyst has the best activity when the hydrothermal synthesis time is 8 h,and the catalyst presents a flower-like structure.Through a series of characterization analysis,specific surface area,surface atomic ratio of Ce³⁺/(Ce³⁺+Ce⁴⁺),acid sites and other factors have a good promotion effect on the denitrification activity.