Comparative Study On Response Properties Of Zeolite Based SCR Catalyst And Vanadium Based SCR Catalyst

As the diesel emission standards become stricter and stricter,NOX emissions of diesel engine cold start stage are strictly limited,and the most widely used vanadium based selective catalyst reduction(SCR)is difficult to meet the requirements of the low temperature region.As a substitude for vanadium,the zeolite based SCR(V-SCR)which showed excellent NOX conversion efficiency,is the main direction of the future development of SCR.But the current research of zeolite based SCR catalyst is mainly about NOX conversion efficiency in steady state,and there is great difference between the transient characteristics and the steady-state characteristics of the zeolite based SCR catalyst,so it is necessary to study the difference in order to ensure the stability of the zeolite based SCR.Through this research,the steady and transient characteristics of the zeolite based and vanadium based SCR on a real engine bench can be obtained,and based on this,the optimized urea injection strategy is put forward,which is the foundation for the research of the zeolite based SCR matching strategy.Evaluation tests of small sample of SCR had been done in the lab to select the catalyst which has the best low-temperature NOX conversion efficiency.Therefore,the ZSM-5 zeolite based SCR was been chosen.Then,the steady-state performance test,the ESC and ETC regulations and the transient response properties of the zeolite based and vanadium based SCR(V-SCR)were carried out by using the diesel engine bench,and based on this,the test to optimized urea injection strategy was carried out.By using the diesel engine bench,the SCR response properties were investigated.The results show that the steady-state characteristics of the two different SCR is amost the same,though the NOX conversion efficiency of Z-SCR catalyst was much higher than the efficiency of V-SCR catalyst when temperature is lower than 250?,but when temperature is higher than 325?,there is no much difference between the two catalysts.The zeolite's storage capacity of NH3 is twice as much as vanadium's.The NOX conversion efficiency of zeolite is better than vanadium under the ETC condition result from the high transient reaction rate of zeolite based SCR.Compared to V-SCR,the transient normal stoichiometric ratio of Z-SCR should be promoted by 0.05 when temperature is lower than 250?,and smaller urea injection delay should be used in the load ramp area.The NOX conversion efficiency of Z-SCR is significantly increased by using the optimized urea injection strategy.