Preparation And Characterization Of Cerium Zirconium Solid Solution Powder By Hypergravity And Study On The Mechanism Of Denitration

NO_X is one of the main components of air pollutants.At present,selective catalytic reduction（SCR）is an effective technology to remove nitrogen oxides.Rare earth catalyst is a promising catalyst in SCR technology.The design and preparation of cerium-based catalysts are suitable for medium and low temperature conditions（280-420℃）and the detailed removal mechanism have become a hotpot in recent years.Based on the high gravity rotating bed technology,micron cerium zirconium solid solution powders with different structures and structures were designed and prepared.The effects of material concentration,calcination temperature,cerium zirconium molar ratio and calcination time on the properties of cerium zirconium solid solution were studied,and the optimum preparation conditions were obtained.At the same time,the morphology and microstructure of cerium zirconium solid solution were further clarified by TG,XRD,scanning electron microscope,catalytic reaction furnace detection,laser particle sizer,specific surface area and pore size measurement instrument.The results showed that the initial concentration of cerium nitrate solution was 0.4mol/l,the molar ratio of cerium nitrate to zirconium oxynitrate was 1:1,the hypergravity condition was 2.68 g,and the precursor was roasted at 600℃for 3h.When the heating rate is 10 K/min,the cerium zirconium solid solution has the smallest particle size and the best crystallization effect,with D₅₀of 14.75μm.The specific surface area is 67.05m²/g,the pore volume is0.322cm³/g and the pore diameter is 21.9nm.The denitration efficiency of the sample is the highest at 350℃,reaching about 71%.In addition,under the framework of Chemkin,this study constructs a detailed chemical reaction mechanism of NO_Xremoval by NH₃selective catalytic reduction.This study also analyzed the reaction path diagram and each reaction rate and researched the influence of intermediate components on the denitration reaction process.The results show that the main reaction equation of denitration is N₂H+NO=N₂+HNO and the key equation of N₂H production is N₂O+H=N₂H+O.That is,N₂O is the main way of N₂H production;In the whole denitration process,the intermediate product N₂H plays a major role in denitration.Finally,by coupling the detailed chemical reaction mechanism and computational fluid dynamics（CFD+Chemkin）,with the help of the material transport model,this study researched the changes of fluid velocity,pressure and mole fraction of each component（flow field,concentration field and pressure field）in the pipeline under the influence of turbulence.The results show that under the condition of high space velocity,there is a large velocity difference in the velocity in the tube,and the interaction and reaction of various reactants accelerate the formation of turbulence in the tube;Chemical reaction interacts with turbulence,which enhances mixing and chemical reaction;In the start-up stage of the reaction,the pressure near the inlet end of the tube was significantly greater than that at the rear end of the tube.At 595 K,620 K and 645 K,the removal rates of NO_Xat the inlet end are 9%,15%and 11%respectively;With the progress of the reaction,the initial NO_Xconcentration in the rear section of the pipe decreases,and the reaction continues.After reaching the steady state,the NO_Xremoval rates at the outlet end are 85%,89%and 84%respectively,which is consistent with the NO_Xremoval mechanism of NH₃selective catalytic reduction with a small amount of hydrogen.