TY - JOUR
T1 - Ammonia Formation over Pd/Rh Three-Way Catalysts during Lean-to-Rich Fluctuations
T2 - The Effect of the Catalyst Aging, Exhaust Temperature, Lambda, and Duration in Rich Conditions
AU - Wang, Chengxiong
AU - Tan, Jianwei
AU - Harle, Gavin
AU - Gong, Huiming
AU - Xia, Wenzheng
AU - Zheng, Tingting
AU - Yang, Dongxia
AU - Ge, Yunshan
AU - Zhao, Yunkun
N1 - Publisher Copyright:
Copyright © 2019 American Chemical Society.
PY - 2019/11/5
Y1 - 2019/11/5
N2 - The formation of ammonia (NH3) as a byproduct during the operation of a three-way catalyst (TWC) in a simulated exhaust stream was investigated using a commercially available Pd/Rh TWC under steady-state and lean/rich cycling conditions. Ion molecular reaction-mass spectrometry was applied to determine NO, NO2, and NH3 concentrations at a time resolution of 0.6 s. Catalyst aging was shown to result in a significant increase in the amount of NH3 formed, which has received limited attention in the literature to date. The selectivity toward NH3 formation has been shown to increase with the decrease in the oxygen storage capacity (OSC) of a TWC induced by thermal aging. NH3 has been shown to mainly form within the exhaust temperature range of 250-550 °C. Typical lambda and rich operational condition duration periods found in vehicle test procedures were also employed to investigate their effects on NH3 formation. The results suggest that a decrease in the lambda and/or an increase in the duration of rich operating conditions will lead to an increase in the selectivity toward NH3 formation. Improving the OSC of TWCs and effectively controlling the lambda near to 1.0 with limited duration in rich operating conditions are therefore significant factors in the reduction of NH3 emissions.
AB - The formation of ammonia (NH3) as a byproduct during the operation of a three-way catalyst (TWC) in a simulated exhaust stream was investigated using a commercially available Pd/Rh TWC under steady-state and lean/rich cycling conditions. Ion molecular reaction-mass spectrometry was applied to determine NO, NO2, and NH3 concentrations at a time resolution of 0.6 s. Catalyst aging was shown to result in a significant increase in the amount of NH3 formed, which has received limited attention in the literature to date. The selectivity toward NH3 formation has been shown to increase with the decrease in the oxygen storage capacity (OSC) of a TWC induced by thermal aging. NH3 has been shown to mainly form within the exhaust temperature range of 250-550 °C. Typical lambda and rich operational condition duration periods found in vehicle test procedures were also employed to investigate their effects on NH3 formation. The results suggest that a decrease in the lambda and/or an increase in the duration of rich operating conditions will lead to an increase in the selectivity toward NH3 formation. Improving the OSC of TWCs and effectively controlling the lambda near to 1.0 with limited duration in rich operating conditions are therefore significant factors in the reduction of NH3 emissions.
UR - http://www.scopus.com/inward/record.url?scp=85074420506&partnerID=8YFLogxK
U2 - 10.1021/acs.est.9b03893
DO - 10.1021/acs.est.9b03893
M3 - Article
C2 - 31577131
AN - SCOPUS:85074420506
SN - 0013-936X
VL - 53
SP - 12621
EP - 12628
JO - Environmental Science and Technology
JF - Environmental Science and Technology
IS - 21
ER -