Photoassisted NH₃-SCR Denitrification Performance Of Supported Vermiculite Based Catalysts

Nitrogen oxide（NO_x）is one of the main pollutants in flue gas emissions,which will cause serious environmental pollution,such as photochemical smog,haze,greenhouse effect,and even threaten human health.In order to reduce NO_xemission,vanadium and titanium series materials are usually used as catalysts,ammonia（NH₃）is used as the raw gas,and selective catalytic reduction（SCR）technology is used to remove NO_x.However,NH₃-SCR technology still has shortcomings such as high reaction temperature and high catalyst toxicity.In recent years,photo-assisted catalysis technology has attracted extensive attention of researchers due to its advantages of low reaction temperature and abundant solar resources.Among them,the semiconductor material TiO₂has the advantages of excellent band width,low cost and environmental friendliness,and is usually used as the active component of photocatalyst or metal assistant.In this thesis,TiO₂was used as a metal promoter and active component espectively to explore the influence of photo assisted NH₃-SCR denitrification performance,and verify the reaction path and mechanism of photocatalyst through density functional theory calculation.The main work contents are as follows:（1）Study on the Photoassisted NH₃-SCR Denitration Performance and Dual Active Center Mechanism of Mn-M/VMT（M=Ti,Co）Mn-M/VMT（M=Ti,Co）photocatalyst was prepared by impregnation method with two-dimensional expanded vermiculite as the carrier,Mn O_xas the active component,TiO_xand Co O_xas the metal additives,which was used to remove NO by photo-assisted NH₃-SCR.It was found that the catalytic reaction activities of Mn/VMT,Mn-Co/VMT and Mn-Ti/VMT were improved to varying degrees under light conditions.Especially,the NO conversion rate of Mn-Ti/VMT catalyst reached 100%at 25～300℃,showing excellent low-temperature catalytic activity.In addition,the Mn-Ti/VMT catalyst has a suitable band gap width（2.07 e V）and a wide light absorption range,which is conducive to the photocatalytic reaction.In addition,through in situ infrared characterization and density functional theory calculation,it was found that the synergistic effect between Mn-Ti enhanced the acid site of the catalyst and promoted the NH₃-SCR reaction.Finally,it is also known that the Mn Ti/VMT catalyst under light conditions follows the Langmuir-Hinshelwood（L-H）mechanism at 200℃.（2）The Effect of MO_x/VMT（M=Ti,Co）Single Component Active Center Photoassisted on SCR Denitration PerformanceMO_x/VMT（M=Ti,Co）photocatalyst was prepared by impregnation method using two-dimensional expanded vermiculite as carrier,TiO_xand Co O_xas active components,which was used to remove NO by photo-assisted NH₃-SCR.It was found that under light conditions,the catalytic activity of Co₃O₄/VMT catalyst was significantly improved,with a high NO conversion rate,while the catalytic activity of TiO₂/VMT catalyst was inhibited,and the NO conversion rate was significantly reduced.In addition,Co₃O₄/VMT catalyst has suitable energy band width（1.72 e V）and higher carrier density,which is more conducive to photocatalytic NH₃-SCR reaction.In addition,the Lewis acid site of Co₃O₄/VMT catalyst was enhanced by light conditions and the NH₃-SCR reaction activity was promoted by in situ DRIFTS characterization and density functional theory（DFT）calculation.At the same time,the energy barrier to be overcome in the speed determination step of NH₃-SCR reaction of Co₃O₄/VMT catalyst under light is 4.41e V,which is easy to further react.However,the acid sites of TiO₂/VMT catalyst decreased after irradiation,and the energy barrier required to overcome in the rate-determining step of the reaction was 4.72 e V,which made it difficult for the reaction to take place in the dark.Finally,it can be seen that Co₃O₄/VMT catalyst follows the Eley-Rideal（E-R）mechanism.