Promotional Effect of La in the Three-Way Catalysis of La-Loaded Al2O3-Supported Pd Catalysts (Pd/La/Al2O3),ACS Catalysis

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Promotional Effect of La in the Three-Way Catalysis of La-Loaded Al2O3-Supported Pd Catalysts (Pd/La/Al2O3)
ACS Catalysis ( IF 11.3 ) Pub Date : 2019-12-26 , DOI: 10.1021/acscatal.9b03766
Yuan Jing ₁ , Zhengxu Cai ₁ , Chong Liu ₁ , Takashi Toyao _{1,

2} , Zen Maeno ₁ , Hiroyuki Asakura _{2,

3} , Satoru Hiwasa ₄ , Shuhei Nagaoka ₅ , Hiroshi Kondoh ₄ , Ken-ichi Shimizu _{1,

2}

Affiliation

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 NO_x (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 Pd⁰ 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 ∼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.

中文翻译：

La在负载La的Al ₂ O ₃担载的Pd催化剂（Pd / La / Al ₂ O ₃）的三效催化中的促进作用

载有La的Al ₂ O ₃（La / Al ₂ O ₃）是三元催化（TWC）反应的实用载体。尽管已经报道了向Al ₂ O _3中添加La导致改善的热稳定性以保持高的比表面积，但是尚未系统地研究其对NO _x（DeNO _x）的催化还原的作用。本文中，我们描述了La在La / Al ₂ O ₃负载的Pd催化剂（Pd / La / Al ₂ O ₃）用于TWC反应。为此，我们结合密度泛函理论，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）和近环境X射线光电子能谱（NAP-XPS）（DFT）计算。所得结果表明，与不具有La（Pd / Al ₂ O ₃）的原始Al ₂ O ₃上的那些相比，负载在La / Al ₂ O ₃上的Pd ⁰种类的电子更多。使用粉末状催化剂的动力学研究表明，添加La可以抑制DeNO _x期间CO的中毒作用反应。除了用粉末状催化剂进行的催化试验外，还制备了整体蜂窝形式的催化剂并将其用于TWC反应，这表明Pd / La / Al ₂ O ₃表现出比Pd / Al ₂ O ₃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，为了保持La / Al ₂ O ₃载体的高比表面积，对于TWC工艺，La的传统负载量通常为La的约3-5 wt％。我们的研究表明，增加的拉负荷（15％重量）是更加有效的DENO _X由于对NO的反应性更高，并且对CO的毒害作用得到了更大的抑制，因此在本研究中测试了这些反应。开发的催化剂Pd / La（15）/ Al ₂ O ₃也已经在商用车辆中进行了测试，并在一个实用的驾驶模式测试循环（LA-4；美国联邦和加利福尼亚州的城市循环），在该循环中显示出比常规使用的Pd / La（3-5）/ Al ₂ O ₃催化剂更好的催化性能。我们的研究表明，Pd / La / Al ₂ O ₃催化剂中La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），还要考虑TWC工艺中的促进作用。

更新日期：2019-12-27

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