Promotional Effect of La in the Three-Way Catalysis of La-Loaded Al2O3-Supported Pd Catalysts (Pd/La/Al2O3)
Promotional Effect of La in the Three-Way Catalysis of La-Loaded Al2O3-Supported Pd Catalysts (Pd/La/Al2O3)
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DOI：
10.1021/acscatal.9b03766
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发表时间：
2020-01-17
期刊：
影响因子：
12.9
通讯作者：
Shimizu, Ken-ichi
中科院分区：
文献类型：
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作者：
Jing, Yuan;Cai, Zhengxu;Shimizu, Ken-ichi
La/Al 2 O3是一种具有实用价值的三效催化剂载体。虽然已经报道了向Al 2 O3中添加La导致改善的热稳定性以保持高的比表面积，但是其对NOx（DeNO（x））的催化还原的影响尚未被系统地研究。在此，我们描述了La在La/Al_2O_3负载的Pd催化剂（Pd/La/Al_2O_3）中用于TWC反应的作用。为此，我们采用了各种原位光谱研究，包括红外（IR），X射线吸收精细结构（XAFS），近环境压力X射线光电子能谱（NAP-XPS）结合密度泛函理论（DFT）计算。结果表明，负载在La/Al 2 O3上的Pd-0比负载在无La的Al 2 O3上的Pd-0更缺电子.动力学研究表明，La的加入抑制了DeNO（x）反应中CO的中毒效应。除了粉末状催化剂的催化性能测试外，还制备了蜂窝状催化剂，并将其应用于TWC反应，结果表明Pd/La/Al 2 O3比Pd/Al 2 O3具有更高的DeNO（x）活性。在这项研究中，我们还重新检查了La的有效负载量，传统上类似于3- 5wt%的La用于TWC工艺，以保持La/Al 2 O3载体的高比表面积。我们的研究表明，增加La负载量（15 wt %）对于本研究中测试的DeNO（x）反应甚至更有效，这是由于对NO的更高反应性和对CO的中毒效应的更大抑制。所开发的催化剂Pd/La（15）/Al 2 O3也已经在商用车辆中进行了测试，并且已经在实际驾驶模式测试循环中进行了评估（LA-4;美国联邦和加州的城市循环），其中它显示出比常规使用的Pd/La（3-5）/Al 2 O3催化剂更好的催化性能。我们的研究表明，在Pd/La/Al 2 O3催化剂中的负载量需要根据应用系统进行调整，不仅要考虑载体的稳定性（表面积），但也在TWC过程中的促进作用。
La-loaded Al2O3 (La/Al2O3) is a practical support for three-way catalysis (TWC) reactions. Although it has been reported that the addition of La to Al2O3 results in improved thermal stability to retain high specific surface areas, its effect on the catalytic reduction of NOx (DeNO(x)) has not been studied systematically. Herein, we describe the role of La in La/Al2O3-supported Pd catalysts (Pd/La/Al2O3) for TWC reactions. For that purpose, we employed various in situ spectroscopic studies, including infrared (IR), X-ray absorption fine structure (XAFS), and near-ambient-pressure X-ray photoelectron spectroscopy (NAP-XPS) in combination with density functional theory (DFT) calculations. The obtained results revealed that Pd-0 species supported on La/Al2O3 are more electron-deficient compared to those on pristine Al2O3 without La(Pd/Al2O3). Kinetic studies using powdered catalysts revealed that the addition of La suppresses the poisoning effect by CO during the DeNO(x) reactions. In addition to the catalytic tests with powdered catalysts, monolithic honeycomb forms of the catalysts were prepared and employed for TWC reactions, which showed that Pd/La/Al2O3 exhibits higher DeNO(x) activity than Pd/Al2O3. In this study, we also reexamined the effective loading amount of La, which has traditionally been similar to 3-5 wt % of La for TWC processes in order to retain the high specific surface area of the La/Al2O3 supports. Our investigations showed that an increased La loading (15 wt %) is even more effective for the DeNO(x) reactions tested in this study due to the higher reactivity toward NO and the greater suppression of the poisoning effect of CO. The developed catalyst Pd/La(15)/Al2O3 has also been tested in a commercial vehicle and has been evaluated on a practical driving mode test cycle (LA-4; city cycle of U.S. Federal and California), where it showed a better catalytic performance than the conventionally used Pd/La(3-5)/Al2O3 catalysts. Our study suggests that the loading amount of La in Pd/La/Al2O3 catalysts needs to be adjusted depending on the application systems, considering not only the support stability (surface areas) but also the promotional effect in the TWC process.