Roles of the basic metals La, Ba, and Sr as additives in Al2O3-supported Pd-based three-way catalysts
Roles of the basic metals La, Ba, and Sr as additives in Al2O3-supported Pd-based three-way catalysts
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DOI：
10.1016/j.jcat.2021.06.016
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发表时间：
2021-08
影响因子：
7.3
通讯作者：
Yuan Jing;Gang Wang;Kah Wei Ting;Z. Maeno;Kazumasa Oshima;S. Satokawa;Shuhei Nagaoka;K. Shimizu;Takashi Toyao
中科院分区：
文献类型：
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作者：
Yuan Jing;Gang Wang;Kah Wei Ting;Z. Maeno;Kazumasa Oshima;S. Satokawa;Shuhei Nagaoka;K. Shimizu;Takashi Toyao
三效催化转化器被广泛用于控制汽油动力汽车的排放。尽管在过去的40多年里，人们已经发现了几种可以提高三效催化剂(TWCS)热稳定性的金属添加剂，但它们对实际催化过程的影响还没有得到系统的研究。本工作通过各种光谱和动力学研究，考察了典型的碱金属添加剂La、Ba和Sr在Pd基TWC体系中的作用。金属Pd0物种在Sr/Al_2O_3和Ba/Al_2O_3载体上比在原始Al_2O_3载体上更富电子，而在La/Al_2O_3载体上则更缺乏电子。因此，在NO还原反应中，Pd/La/Al_2O_3具有减轻CO中毒的作用。在模拟实际使用的条件下，使用粉末催化剂和整体式蜂窝催化剂进行了评估。Pd/La/Al_2O_3对NO的催化还原效果最好，而Pd/Ba/Al_2O_3对CO和C_3H_6的氧化活性最高。目前的数据表明，Pd基TWC的最佳金属添加剂将根据具体应用而定。在选择这类金属时，不仅要考虑其稳定性，还应考虑其在尾气净化过程中的促进作用。
Three-way catalytic converters are widely used to regulate emissions from gasoline-powered vehicles. Although significant effort over the past 40 years has resulted in the discovery of several metal additives that improve the thermal stability of three-way catalysts (TWCs), their effects on the actual catalytic process have not been studied systematically. The present work examines the roles of the typical basic metal additives La, Ba, and Sr in Pd-based TWC systems, using various spectroscopic and kinetic studies. Metallic Pd0species on Sr/Al2O3and Ba/Al2O3supports were found to be more electron-rich than those on pristine Al2O3, whereas those on La/Al2O3were more electron-deficient. Consequently, Pd/La/Al2O3showed a lessened CO poisoning effect during NO reduction reactions. Evaluations were performed using powdered catalysts as well as monolithic honeycomb catalysts under conditions simulating actual use. Pd/La/Al2O3was observed to promote the catalytic reduction of NO most efficiently, while Pd/Ba/Al2O3exhibited the highest activity for the oxidations of CO and C3H6. The present data suggest that the optimal metal additive for a Pd-based TWC will be determined by the specific application. The selection of such metals should take into account not only the stability but also the promotional effect during the exhaust purification process.