关键词: Cu-CHA型分子筛, 选择催化还原, NO _x 反应速率, 氨存储特性, 氨泄漏

Abstract:

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 NO _x conversion efficiency and ammonia storage characteristics 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 NO _x 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^-6 mol/s and 1.48×10^-5 mol/s，respectively.Low SAR，high load，and high cell density schemes could improve the transient NO _x conversion rate at a single point，reduce the transient ammonia storage capacity.Improving ANR could simultaneously enhance transient NO _x conversion rate and transient ammonia storage capacity.The NO _x emissions under different operating conditions were consistent with the low-temperature single point performance，but the high load scheme enhanced the NH₃ leakage under changing operating conditions，which was opposite to the trend of NH₃ leakage at a single point performance.

Key words: Cu-CHA zeolite, selective catalytic reduction, NO _x reaction rate, ammonia storage characteristics, NH₃ slip