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Ammonia Formation over Pd/Rh Three-Way Catalysts during Lean-to-Rich Fluctuations: The Effect of the Catalyst Aging, Exhaust Temperature, Lambda, and Duration in Rich Conditions
Environmental Science & Technology ( IF 10.8 ) Pub Date : 2019-10-21 , DOI: 10.1021/acs.est.9b03893 Chengxiong Wang 1, 2 , Jianwei Tan 3 , Gavin Harle 2 , Huiming Gong 3 , Wenzheng Xia 2 , Tingting Zheng 1, 2 , Dongxia Yang 2 , Yunshan Ge 3 , Yunkun Zhao 1, 2
Environmental Science & Technology ( IF 10.8 ) Pub Date : 2019-10-21 , DOI: 10.1021/acs.est.9b03893 Chengxiong Wang 1, 2 , Jianwei Tan 3 , Gavin Harle 2 , Huiming Gong 3 , Wenzheng Xia 2 , Tingting Zheng 1, 2 , Dongxia Yang 2 , Yunshan Ge 3 , Yunkun Zhao 1, 2
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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.
中文翻译：
贫富波动期间Pd / Rh三效催化剂上氨的形成：富化条件下催化剂老化，排气温度，Lambda和持续时间的影响
使用市售的Pd / Rh TWC在稳态和稀/富循环条件下研究了三元催化剂（TWC）在模拟废气流中运行过程中副产物氨（NH 3）的形成。应用离子分子反应质谱法以0.6 s的时间分辨率确定NO，NO 2和NH 3的浓度。催化剂老化被证明会导致NH 3形成量的显着增加，迄今为止在文献中只受到了有限的关注。已经显示出对NH 3形成的选择性随着由热老化引起的TWC的储氧能力（OSC）的降低而增加。NH 3已证明主要在250–550°C的排气温度范围内形成。在车辆测试程序中发现的典型的λ和丰富的运行条件持续时间也被用来研究其对NH 3形成的影响。结果表明，λ减小和/或浓运行条件持续时间的增加将导致对NH 3形成的选择性增加。因此，改善TWC的OSC并在丰富的运行条件下在有限的持续时间内有效地将λ控制在1.0附近是减少NH 3排放的重要因素。
更新日期：2019-10-21
中文翻译：
贫富波动期间Pd / Rh三效催化剂上氨的形成：富化条件下催化剂老化，排气温度，Lambda和持续时间的影响
使用市售的Pd / Rh TWC在稳态和稀/富循环条件下研究了三元催化剂（TWC）在模拟废气流中运行过程中副产物氨（NH 3）的形成。应用离子分子反应质谱法以0.6 s的时间分辨率确定NO，NO 2和NH 3的浓度。催化剂老化被证明会导致NH 3形成量的显着增加，迄今为止在文献中只受到了有限的关注。已经显示出对NH 3形成的选择性随着由热老化引起的TWC的储氧能力（OSC）的降低而增加。NH 3已证明主要在250–550°C的排气温度范围内形成。在车辆测试程序中发现的典型的λ和丰富的运行条件持续时间也被用来研究其对NH 3形成的影响。结果表明，λ减小和/或浓运行条件持续时间的增加将导致对NH 3形成的选择性增加。因此，改善TWC的OSC并在丰富的运行条件下在有限的持续时间内有效地将λ控制在1.0附近是减少NH 3排放的重要因素。
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