Synthesis Of The Modified Vanadium-based Catalysts For Selective Catalytic Reduction Of NO

In recent years,the elimination or degradation of nitrogen oxides?NOx?,the major pollutants of the atmosphere,has been attracted extensive attention.Numerous methods have been studied and used to eliminate the nitrogen oxides,and the selective catalytic reduction?SCR?,using ammonia as the reducing agent,is an effective method to remove nitrogen oxides.Currently,the V₂O₅-WO₃/TiO₂-based catalyst has a narrow and high working temperature window of 300-400 ^oC.The flue gas temperatures for industrial processes is usually below 300°C,the SCR system needs to be heated above 300°C with the conventional V₂O₅-WO₃/TiO₂ catalyst.As a result,a lot of energy is consumed.Therefore,this paper aims to develop and synthesize modified vanadium-based catalysts with high catalytic activity and wide operation temperature window for the SCR of NOx with NH₃.In this paper,NH₃ as the reducing agent was used to remove NOx.The V-Ce-Ni/TiO₂catalysts were designed and synthesized.The catalytic performance of the catalysts prepared using plasmaa-assisted treated and the citric acid was investigated.Meanwhile,the structure of the catalyst was characterized by XRD,BET,TPD,TPR,SEM+mapping,TEM,XPS and so on.Specifically include the followings:?1?A serials of V-Ce-Ni/TiO₂ catalysts were prepared using the ultrasonic-assisted method by optimizing the doping amount of active components and assistants,and its catalytic activities in NH₃-SCR reaction were investigated,and the structure of the catalysts were characterized.The results showed that the 3.75V-7Ce-0.1Ni/TiO₂ catalyst showed highest catalytic activity which achieved more than 89%conversion of NO at 200^oC,100%at 300 ^oC and outnumber 90%removal efficiency of NO at the temperature ranging from 202 ^oC to 400 ^oC.The XRD characterization results displayed that V₂O₅,VO₂and NiO species were armorphous structure,and the addition of cerium and nickel could inhibit the crystallization of anatase phase TiO₂.The BET results showed that the vanadium-based catalysts presented mesoporous structure,and nickel and cerium co-modification could increase the specific surface area to some degree.The NH₃-TPD characterization results indicated that the addition of nickel and cerium could increase the amount of acid sites,especially weak acid sites,and then facilitates the adsorption and activation of ammonia,thus enhance the catalytic activity.The characterization results of H₂-TPR indicated that the addition of cerium and nickel contribute to the enhancement of the interaction between active components and support,and cerium and nickel co-modification could effectively improve the redox ability of catalyst,and so extend the operation temperature window and improved the catalytic activity at low-temperature.SEM analysis results showed that the addition of nickel resulted in the formation of crystals with smaller particle size,and the smaller particle size well distributed on the surface.However,the introduction of cerium resulted in the aggregate of part of small particles and increased the particle size.According to SEM-EDS mapping images results,the element distributed evenly and well in 3.75V-7Ce-0.1Ni/TiO₂ catalyst.TEM characterization results showed that these catalysts exhibited 20³0 nm primary particle size and botryoid shape anatase crystal particles,and these catalysts presented good dispersion and similar shape of the particles.The XPS analysis results demonstrated that there was strong interaction among V,Ni and Ce species,the addition of cerium and nickel was contributed to increasing the surface oxygen O_?content of the catalyst and facilitating the oxidation process from NO to NO₂.In addition,the Ce redox sites were more active than V redox sites and play a major role in SCR-NO by NH₃ at low temperature.?2?3.75V-7Ce-0.1Ni/TiO₂ catalysts were prepared using the low temperature plasmaa assisted in the process of synthesis,and plasmaa discharge parameters?such as discharge time and discharge power?and discharge medium?such as N₂ and H₂?were adjusted and optimized,and their catalytic activities in NH₃-SCR reaction were investigated,besides,the structure of the catalysts were characterized.The results showed that the3.75V-7Ce-0.1Ni/TiO₂-HP-4 min catalyst showed highest catalytic activity which achieved more than 95%conversion of NO at 200 ^oC and outnumber 90%removal efficiency of NO at the temperature ranging from 195 ^oC to 414 ^oC and NO conversion of 100%were maintain at 230³50 ^oC.The XRD characterization results displayed that V₂O₅,VO₂ and NiO species were armorphous structure,and N₂ and H₂ plasma assisted treatment could increase and decrease grain size of TiO₂,respeactively.The BET results showed that the vanadium-based catalysts presented mesoporous structure,and N₂ and H₂ plasma assisted treatment could increase and decrease the specific surface area to some degree,respeactively.The NH₃-TPD characterization results indicated that plasma assisted treatment could decline the amount of weak acid sites,but the temperature of desorption peak increased,indicating that the acid strength of the catalyst could be improved using plasmaa assisted treatment.The characterization results of H₂-TPR indicated that N₂plasma assisted treatment was contribute to the enhancement of the interaction between active components and support,and H₂ plasma assisted treatment could effectively improve the redox ability of catalyst.SEM analysis results showed that plasma assisted treatment resulted in the formation of crystals with smaller particle size,and the smaller particle size well distributed on the surface.However,the introduction of cerium resulted in the aggregate of part of small particles and increased the particle size.According to SEM-EDS mapping images results,the element distributed evenly and well in3.75V-7Ce-0.1Ni/TiO₂-HP-4min catalyst.TEM characterization results showed that these catalysts exhibited 20³0 nm primary particle size and the morphology of ellipsoidal particles,and these catalysts presented good dispersion and degree of crystallinity.The XPS analysis results demonstrated that plasmaa assisted treatment enhanced the interaction between V species and support,which resulted in stronger absorb electrons ability.The catalyst prepared using H₂ plasmaa assisted treatment showed higher electron cloud density,which was helpful to promote the ion transforation process and improve the catalytic activity of the catalyst.In addition,plasmaa assisted treatment was contributed to increasing the O_?content of the catalyst and facilitating the oxidation process from NO to NO₂,and then improve the NO conversion,Ce³⁺/(Ce³⁺+Ce⁴⁺)ratio was higher over3.75V-7Ce-0.1Ni/TiO₂-HP-4min catalyst than 3.75V-7Ce-0.1Ni/TiO₂-NP-120W catalyst.?3?The V-Ce-Ni/TiO₂-CA catalysts were prepared using citric acid method,and their catalytic activities in NH₃-SCR reaction were investigated,the structure of the catalysts were characterized.The results showed that the 3.75V-15Ce-0.3Ni/TiO₂-CA catalyst showed that more than 98%conversion of NO at 200 ^oC,over 80%of NO conversion at the temperature ranging from 184 ^oC to 414 ^oC and outnumber 90%removal efficiency of NO at the temperature ranging from 192 ^oC to 402 ^oC was achieved.The XRD characterization results displayed that V,Ce and Ni species were armorphous structure,and these species distributed well in catalyst surface.The BET results showed that the vanadium-based catalysts using citric acid method presented mesoporous structure,and nickel and cerium modification could increase the specific surface area to some degree.The NH₃-TPD characterization results indicated that the addition of cerium could improve the acid strength of the catalyst prepared by citric acid method,and then facilitates the adsorption and activation of ammonia,thus enhance the catalytic activity.The characterization results of H₂-TPR indicated that the addition of cerium was contribute to the enhancement of the interaction between active components and support,but the modification of nickel could effectively improve the redox ability of catalyst,and so improved the catalytic activity and extend the operation temperature window.SEM and SEM-EDS analysis results showed that the addition of cerium and nickel the particle size well distributed on the surface.TEM characterization results showed that the catalyst particles prepared using citric acid method were evenly distributed with good crystallinity and dispersion,and the dispersion of catalyst was further improved due to the introduction of cerium and nickel.The XPS analysis results demonstrated that the number of reduced V species was higher over 3.75V/TiO₂-CA than 3.75V/TiO₂ catalyst prepared by impregnation method.There was a strong interaction among active components,assistants and support.Among these catalysts prepared by citric acid method,the 3.75V/TiO₂-CA catalystshowedthehighestO_?/?O_?+O_??ratio.Comparedwiththe3.75V-15Ce-0.3Ni/TiO₂-CA catalyst,the number of the adsorbed oxygen O_?,reduced V species and reduced Ce species was higher over 3.75V-15Ce/TiO₂-CA catalyst,which was the main reason for the highest denitrification activity and widest operating temperature window of the 3.75V-15Ce/TiO₂-CA catalyst.