Study On Mechanism Of Photocatalytic Performance For NO Removal And Preparation Of Titanium-based Catalysts

In recent years,nitrogen oxides（NO_x）emissions are the one of the reasons of environmental pollution.This causes the increasingly serious environmental problems.Therefore,the country’s requirements for nitrogen oxide emissions are stricter.However,The selective catalytic reduction（SCR）technology,which temperature window is 320-400℃,is not suitable for sintering machines and industrial boilers.Which the exhaust temperature of these industrials is lower.If you want to achieve low-cost flue gas denitrification,the easiest method is to oxidize NO in the flue gas to high soluble NO_x,and then use an alkali solution to remove it.Photocatalysis,as one of the most popular catalytic methods at present.It has the advantages of wide energy sources,cleanliness,and low cost,and has the potential to solve environmental pollution and energy shortages.The semiconductor photocatalyst is the core of photocatalysis.As a semiconductor photocatalyst,titanium dioxide（TiO₂）has excellent properties such as stable performance,low cost,and non-toxicity.Meanwhile,At the same time,TiO₂ catalyst can generate a lot of free radicals under the light,and these free radicals can oxidize NO.Therefore,it is theoretically feasible to apply photocatalysis to remove NO in low-temperature flue gas.In this paper,in order to improve the conversion efficiency of NO at low temperature.TiO₂ was modified by two strategies:increasing specific surface area and increasing active sites,Firstly,large number of TiO₂ nanotube precursors were prepared by a commercial P25catalyst（TiO₂）through a hydrothermal method,Through the wet chemical method,P-TiO₂nanotubes（P-TNTs）were prepared.The ability of this catalyst to remove NO was investigated under UV/H₂O₂ conditions.It was found that the catalytic performance was optimal when the P doping amount was 5 wt%.The structure of P-TNTs was analyzed by XRD,Raman,DRS,TEM and XPS characterization,and it was proved that P was incorporated into the TiO₂ lattice.From the transient reaction,NO-TPD,and H₂O₂-TG,the reasons for the improvement of the photocatalytic efficiency of P-TNTs were analyzed.It was found that the adsorption amount of H₂O₂ and NO on the catalyst surface was significantly enhanced,which improved the NO removal performance of this catalyst in the UV/H₂O₂ system.And the importance of H₂O₂ and NO adsorption for the catalytic performance in the UV/H₂O₂ photocatalytic system was verified.Secondly,in order to make the preparation of active sites easier,oxygen vacancies were selected as the active sites to modify TiO₂.X-B-TiO₂ catalysts containing oxygen vacancies and X-TiO₂ catalysts containing no oxygen vacancies were obtained by calcination at different temperatures and different atmospheres（X represents the calcination temperature）.Under UV/H₂O₂ conditions,the above catalysts were evaluated for NO conversion efficiency under UV/H₂O₂ conditions.The evaluation results showed that TiO₂ obtained under the conditions of400℃calcination temperature and N₂atmosphere had the best catalytic performance.XRD,Raman,DRS,electrochemistry,EPR,etc.were used to characterize and analyze TiO₂containing oxygen vacancies,confirming the existence of oxygen vacancies,and the relative number of oxygen vacancies in each catalyst.400-B-TiO₂ has greatly increased the light absorption range,and has the best separation efficiency of electrons and spacers.In this system,the catalytic performance of TiO₂ calcined at 400°C is the highest.Through the energy band analysis and free radical capture experiments of the catalyst,the synergistic relationship between oxygen vacancy,H₂O₂ and UV removal of NO was clarified.Through the energy band analysis and free radical capture experiments of the catalyst,the synergistic relationship between oxygen vacancy,H₂O₂ and UV removal of NO was clarified.In addition,because the reduced TiO₂（B-TiO₂）has a large response range to light and can absorb visible light（Vis）,the NO conversion efficiency of B-TiO₂ under visible light was tested.However,B-TiO₂ has poor NO conversion efficiency under visible light,in order to improve the catalytic performance of B-TiO₂ under visible light,B-TiO₂ and graphene oxide（GO）were compounded by a simple hydrothermal method.And the ability of NO removal under the Vis/H₂O₂ system was investigated.The result showed that when the GO loading is 3 wt%,the NO conversion efficiency is the highest.By DRS,MS,and photocurrent density characterization,it was found that the combination of GO and catalyst can effectively improve the optical properties,redox potential and electron-hole separation efficiency of B-TiO₂ catalyst.Thereby B-TiO₂-GO catalyst enhanced the NO conversion efficiency.At the same time,the adsorption characteristics of reactive species on the catalyst surface were analyzed by TPD.It was found that the adsorption amount of NO and H₂O₂ both increased.It proves that the composite can increase the adsorption capacity of H₂O₂ and NO.And then,through the free radical capture experiments of EPR,it was clarified that the hydroxyl radicals generated during the reaction are important intermediates to promote NO oxidation.The synergy between H₂O₂,NO,visible light and B-TiO₂-GO is discussed in detail.