Research On Kinetics And Alkali Metal Poisoning Of Mn-Ce/TiO₂ Low-temperature SCR Catalyst

Nitrogen oxides?NO_x?are one of the most common air pollutants,which do harm to the environment and human.At present,high-temperature SCR is the most common technology of NOx-removal,but using SCR catalysts needs high activation temperature,easy to fire during operation,large losses and high cost.In recent years,cement,metallurgy,coking and glass production industry generally recycle fume waste heat.The flue gas temperature is getting lower and lower into the SCR-DeNOx system,so low-temperature denitrification technology becomes the preferred process.It has been shown that the modified Mn-Ce/TiO₂ catalyst has good denitrification performance and has the potential to become commercial catalyst,The study about its kinetics can provide theoretical basis for the subsequent optimization of SCR system.After the flue gas dust removal,the residual trace alkaline dust has a strong effect on the activity of the denitration catalyst.Therefore,it is very important to explore the effect of alkali metal on the activity of the catalyst and its mechanism,which has great significance to improve the ability of the catalyst to resist alkali poisoning and improve the denitrification activity.In this paper,the kinetic study of SCR-denitrification reaction of Mn-Ce/TiO₂ catalyst was carried out from steady-state dynamics.And finally get the reaction kinetic equation.The effects of alkali metal poisoning on the denitrification activity and the activity retention of the catalyst were studied.The catalysts were characterized by BET,SEM,XRD and FT-IR,and the reason of alkali metal poisoning was analysed from different angles.Get the following conclusions:?1?The use of a catalyst with a particle size range of 0.15-0.20 mm for the catalytic reduction reaction is sufficient to eliminate the effect of internal diffusion.When the weight of the catalyst is 6g and 6.5g,the space velocity is 5538-16000h^-1,so there is no external diffusion effect.In the kinetic reaction,NH3 reaction order can be considered as 0,not the rate-determining step.After fitting,O₂ reaction order can be approximated as 0,and NO reaction order is 1.The reaction kinetic parameters of Mn-Ce/TiO₂ catalyst are: reaction activation energy Ea=20135.93J·mol-1,pre-exponential factor A=52052.08 cm³·g^-1·min^-1.The reaction rate equation is:rNO =52052.08exp?-20135.93/RT?CNO.?2?The denitrification efficiency of Mn-Ce/Ti O₂ catalyst decreased after alkali metal poisoning,and its efficiency decreased with the increase of alkali metal content.Furthermore,and the degree of inactivation of potassium poisoning was higher than that of sodium.The denitrification efficiency decreased with the increase of alkali metal content.The specific surface area of the catalyst for alkali metal poisoning is significantly reduced,which potassium poisoning catalyst decreased by 34.2%.Both BET and SEM characterization indicated that the alkali metal poison clogged the pores on the surface of the catalyst and reduced the denitrification efficiency.The XRD pattern shows that the catalyst carriers of Na poisoning and K poisoning are partially converted to rutile type,which is not conducive to the expression of catalyst activity.The bending vibration band and stretching vibration band of H-O appeared before and after alkali metal poisoning at 3443cm^-1 and 1636cm^-1.The bending vibration band of NH₄⁺ which adsorbed on the acidic sites of the catalyst appeared at 1401cm^-1.Functional groups have no significant change.?3?Changing the average particle size of the catalyst had no significant effect on the activity retention.The activity retention fraction of the catalyst with different alkali mass fraction increases with the increase of temperature,but also has the active temperature window.With the increase of alkali metal content,the activity retention of the catalyst decreases.The introduction of Cl^-and SO₄^2- decreases the reaction rate of the catalyst to varying degrees,and the influence degree of the two is different at different temperatures.