Research on NH3-SCR performance and ammonia storage characteris-tics based on different Cu-CHA catalyst schemes
To investigate the effects of coating silicon aluminum ratio(SAR),loading amount,cell density of substrate scheme,and ammonia/nitrogen oxide molar ratio(ANR)on transient NOx conversion efficiency and ammonia storage char-acteristics of SCR catalysts,Cu-CHA coatings with SAR=12 and 22 were prepared by ion exchange method.Four coating catalyst schemes were prepared by combining loading amounts of 140 g/L and 160 g/L,62 pores/cm2 and 93 pores/cm2 mesh size carriers.Through NH3-TPD/H2-TPR characterization of the material,it was found that the SAR=12 coating had more active Cu2+and more acidic sites.The transient single point performance and operating condition emissions of SCR were studied using a fixed bed reactor and an engine bench,respectively.Single point performance studies showed that the low-temperature NOx reaction rates of each scheme were 12-160-93,12-160-62,12-140-62,22-160-62.Under the 12-160-93 scheme,the average single point reaction rates at 180 ℃,200 ℃,and 250 ℃ could reach 2.24 ×10-6 mol/s,4.37×10-6mol/s and 1.48×10-5 mol/s,respectively.Low SAR,high load,and high cell density schemes could improve the transient NOx con-version rate at a single point,reduce the transient ammonia storage capacity.Improving ANR could simultaneously enhance transient NOx conversion rate and transient ammonia storage capacity.The NOx emissions under different operating condi-tions were consistent with the low-temperature single point performance,but the high load scheme enhanced the NH3 leak-age under changing operating conditions,which was opposite to the trend of NH3 leakage at a single point performance.
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