Study On SCR Catalysts For The De-no_x Of Diesel Exhaust

With the increasingly"diesel"of automotive power,that nitrogen dioxide?NO_X?pollution caused by exhaust emissions from diesel vehicles is becoming increasingly prominent,and the requirements for diesel emission standards are becoming more strict.In this situation,Urea/NH₃-SCR has become one of the most effective NO_X control technologies of diesel enging.Compared with metal oxide,noble metal and other zeolite catalysts,because of the high specific surface area and strong acidity of ZSM-5 catalyst,which is the most promising kind of catalyst for SCR denitrification.In this paper,the preparation methods of single metal modification and bimetallic modified molecular sieve powder catalyst and cordierite honeycomb ceramic and the preparation and evaluation of monolithic catalyst has been studied by respectively.Which provides theoretical support for the research of nano-ZSM-5 zeolite-based catalyst.for de-NO_X.The relationship between the loading of copper and the de-NO_X efficiency of Cu/ZSM-5catalyst with different SiO₂/Al₂O₃ ratio has been investigated.It was found that the de-NO_X efficiency of Cu/ZSM-5 decreased with the increase of SiO₂/Al₂O₃ ratio of ZSM-5.The de-NO_X efficiency of 2.5%Cu/ZSM-5?25?is the highest,that can be removed by 80%in the temperature of 175⁴20?.It has been founs that the density of acid decreased with the increase of ratio of SiO₂/Al₂O₃ by Py-IR analysis.The Bronsted acid and Lewis acid peak area ratio may be the key factor to affect the efficiency of de-NO_X.The Cu/ZSM-5 doped with different transition metal of Ce,Zr,Fe was prepared with the methed of equal volume impregnation to improve the activity of the catalyst.The experimental results that showed the temperature activity window of copper-based catalyst was greatly broadened by doped cerium and zirconium and iron,that also improved the low temperature efficiency of de-NO_X.The results of SO₂ resistance test of optimal catalysts showed that have excellent resistance ability in high temperature,but their resistance need to be improved in low temperature,The analysis showed that may be related to Bronsted acid sites.The strong acid quantity has been decreased after modified by transition metal,that affected the adsorption and desorption strength in the acid site of NH₃.The research showed that the newly deoped species may be affect the reduction temperature of CuOx,which affects the Cu⁺/Cu²⁺ratio.The results of studied on cordierite honeycomb ceramics and monolithic catalysts have showed that possible to produce honeycomb ceramics with excellent properties when the raw and clinker ratio was 1:9.The results of the characterization of the honeycomb ceramics and the coating rate test of monolithic catalysts showed that the specific surface area of self-made honeycomb ceramic is higher than the currently commercial honeycomb.Compared with the evaluations of monolithic catalysts of de-NO_X showed that the activity of monolithic catalysts with self-made carrier was significantly higher than that of the commercial ceramic carrier catalysts.The experimental results showed that the activity of monolithic catalysts was affected by the carrier and the relationship between the coating rate at a certain range.