Study On The Synthesis Of Nb-based Catalysts For Low Temperature Selective Catalytic Reduction Of NO

Nitrogen oxides?NO_X?emitted from the exhaust of coal-fired power plants are one of the main pollutants in the atmosphere.NH₃ selective catalytic reduction technology?NH₃-SCR?is considered to be the most effective technology to reduce NO_X emissions.Among them,V₂O₅-WO₃/TiO₂ is the most widely used commercial catalyst.However,commercial V-based catalysts have exposed some problems during industrial applications,such as poor low temperature activity and a narrow operating temperature range of300⁴00?.Therefore,the current research trend is to develop efficient and environmentally friendly V-free denitration catalysts.Nb element is widely used in NH₃-SCR reaction because it is in the same group as V,has similar properties to V,is less toxic than V,and has a unique acidity.Most of the existing studies have doped Nb as a promoter into the catalyst,but will NH₃-SCR catalysts with Nb as the active component in the NH₃ system still have excellent low-temperature catalytic activity?Therefore,this paper aims at the problems of poor low-temperature activity and narrow operating temperature window of commercial catalysts.By designing and synthesizing new high-efficiency Nb-based catalysts,the purpose is to improve the low-temperature activity of catalysts and widen the operating temperature window of catalysts.This paper focuses on designing and synthesizing a new Nb-based catalyst for removing nitrogen oxides from the tail gas of coal-fired power plants with Nb as the active component and TiO₂ as the support of Nb-based catalysts.At the same time,the catalysts were characterized by XRD,BET,etc.to explore the catalyst structure.The main research contents are as follows:1.A serials of Nb-Fe-Ce/TiO₂ catalysts were synthesized by adjusting the loading assistant,and its catalytic activity in NH₃-SCR reaction was studied and its structure was characterized.The results showed that 10%Nb-7%Ce-0.7%W/TiO₂ catalyst showed highest de-NO_X performance,which achieved 100%conversion at 300?,and the operating temperature window of catalyst is T₈₀=200⁵00?.By analyzing the structure?XRD?and texture?BET?of the catalyst,the characterization results showed that the active component Nb and the metal oxides of active component Nb,active additives Fe and Ce were highly dispersed on the surface of TiO₂ support.After the additives Fe and Ce were introduced,interactions existed among the active components Nb,additives Ce and Fe,and the support TiO₂,which promoted the reduction of the anatase phase TiO₂ crystallite size;with the introduction of Ce could improve the specific surface area and average pore size of catalyst.With the co-introduction of Fe and Ce,the specific surface area of the catalyst decreased and the average pore size increased,indicating that one,two,or three of Nb,Fe,and Ce have been supported on the TiO₂ support and were highly dispersed in on TiO₂support,so that 10%Nb-0.7%Fe-3%Ce/TiO₂ catalyst showed the best de-NO_X performance.2.Based on the above studies,a serials of Nb-Ce-W/TiO₂ catalysts were synthesized by the impregnation method,and its catalytic activity in NH₃-SCR reaction was studied,and its structure and texture were analyzed.The results showed that the10%Nb-7%Ce-0.7%W/TiO₂ catalyst showed the best de-NO_X performance,which achieved 100%conversion from 250?to 400?,and the operating temperature window of catalyst was T₈₀=200⁵00?.By analyzing the structure?XRD?and texture?BET?of the catalyst,the results showed that the metal oxides of active component Nb and active additives Ce and W were highly dispersed on the surface of TiO₂.After the introduction of additives Ce and W,The interaction among the active component Nb,active additives Ce,W and the support TiO₂ promoted the reduction of the anatase phase TiO₂ crystallite size;All catalysts still maintained the mesoporous structure of the TiO₂,The separate introduction of Ce and W can increase the pore volume and average pore diameter of catalyst.With the co-introduction of Ce and W,the specific surface area of the catalyst decreased and the average pore size increased,indicating that one,two,or three of Nb,Ce,and W have been supported on the support TiO₂,so that 10%Nb-7%Ce-0.7%W/TiO₂catalyst showed the best denitration performance.3.A serials of Nb-Ce-Zr/TiO₂ catalysts were synthesized by impregnation method,and its catalytic activity in NH₃-SCR reaction was studied,and its structure and texture were analyzed.The results showed that the 10%Nb-7%Ce-0.7%Zr/TiO₂ catalyst exhibited highest denitration performance,which achieved 100%conversion from 250?to 450?,and the operating temperature window of catalyst was T₈₀=210⁵00?.By analyzing the structure?XRD?and texture?BET?of the catalyst,the results showed that the active component Nb,active additives Ce and Zr were highly dispersed on the surface of TiO₂.After the introduction of Zr,the interaction among the active component Nb,the active promoters and the support TiO₂ was enhanced,and the size of the anatase TiO₂ crystallite was reduced;all catalysts still maintained the mesoporous structure of the TiO₂ support.With the introduction of Ce and Zr,specific surface area of the 10%Nb/TiO₂ catalyst was reached,whereby the 10%Nb-7%Ce-0.7%W/TiO₂ catalyst showed the best denitration performance.