Effect of the morphological and surface properties of CeO2-based catalysts on the soot oxidation activity
Effect of the morphological and surface properties of CeO2-based catalysts on the soot oxidation activity
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DOI：
10.1016/j.cej.2014.10.055
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发表时间：
2015-10-15
影响因子：
15.1
通讯作者：
Fino, D.
中科院分区：
文献类型：
--
作者：
Miceli, P.;Bensaid, S.;Fino, D.
在柴油机颗粒过滤器中，会发生固体（烟灰）-固体（催化剂）反应，在这些情况下，催化剂形态起着相关作用，接触点的数量是最终反应速率的关键特征。因此，本工作研究了两种不同的二氧化铈基催化剂形态，用于烟灰氧化反应：首先，通过溶液燃烧合成 (SCS) 制备二氧化铈催化剂，其比表面积为 29 m(2)/g。另一方面，三维自组装（SA）星状二氧化铈，因其从中心核开始的分支形态而被称为，表现出更高的比表面积（124 m(2)/g），由于所获得的形态的凹面和有趣的纳米级表面特征，烟灰颗粒和催化剂本身之间的接触点具有高可用性。对合成方法进行了调整，以在形状和尺寸方面达到所需的明确形态。还考虑了老化的星形，以便充分评估这种新材料相对于经典SCS催化剂的优缺点。与SCS二氧化铈催化剂相比，SA星形具有更高的微孔体积，约为0.04 cm(3)/g，以及更细的晶粒尺寸。 SA 星对烟灰氧化表现出更好的活性：在紧密接触条件下，峰值氧化温度从 614 摄氏度（非催化情况下）降至 403 摄氏度，在松散接触条件下降至 552 摄氏度。 XPS 分析表明，这可能是由于与 SCS 氧化铈相比具有更高的表面氧利用率，而 HRTEM 表明表面微晶显示出氧缺陷结构，在 SCS 催化剂表面几乎不存在，这也可能涉及更高的氧化还原能力。在松散接触条件下，这是最现实的测试条件，因为烟灰沉积在柴油颗粒过滤器的催化层上，无需施加任何力，SA 星即使在老化后也表现出最低的起始温度，从而证明了其更高的固有活性。此外，在紧密接触条件下，老化星体的活性低于新鲜SCS粉末，但由于SA星体形态特有的捕获烟灰颗粒的内在能力，在松散的星体中恢复了良好的效果。从在柴油颗粒过滤器中应用这种工程形态的角度来看，SA星体的三维形状可能涉及滤饼层和催化剂层之间接触点数量的增加，从而促进最终活性。 (C) 2014 Elsevier B.V. 保留所有权利。
In diesel particulate filters, a solid (soot)-solid (catalyst) reaction occurs and, in these cases, the catalyst morphology plays a relevant role, being the number of contact points a critical feature for the resulting reaction rate.For this reason, two different ceria-based catalyst morphologies have been investigated in this work, for the soot oxidation reaction: first, a ceria catalyst was prepared by solution combustion synthesis (SCS), which lead to a specific surface area of 29 m(2)/g. On the other hand, three-dimensional self-assembled (SA) stars ceria, so-called due to their branched morphology starting from a central nucleus, exhibited a higher specific surface area (124 m(2)/g), a high availability of contact points between soot particles and the catalyst itself, due to the concavities of the obtained morphology, and interesting surface features at the nanoscale. The synthesis method was tuned in order to resort to a desired and well-defined morphology in terms of shape and size.Aged stars were also taken into account, in order to fully evaluate the advantages and drawbacks of this new material against classic SCS catalysts.Compared to the SCS ceria catalyst, the SA stars have a much higher microporous volume, being of about 0.04 cm(3)/g, and a finer crystallite size. SA stars showed a better activity towards soot oxidation: the peak oxidation temperature dropped from 614 degrees C (in the non-catalytic case) to 403 degrees C in tight contact conditions, and to 552 degrees C in loose ones. XPS analysis elucidated that this can be due to a higher surface oxygen availability as compared to SCS ceria, while HRTEM revealed that surface crystallites show oxygen defective structures, almost absent at the SCS catalyst surface, which also might involve a higher redox capability.In loose contact conditions, being the most realistic testing condition because soot deposits on the catalytic layer of the diesel particulate filter without any force exertion, the SA stars exhibited the lowest onset temperature, even after aging, thus proving their higher intrinsic activity. Moreover, aged stars, which are less active than fresh SCS powders in tight contact conditions, regain good results in the loose ones, thanks to intrinsic capability to catch soot particles, peculiar of the SA star morphology.In the perspective of applying such engineered morphologies in diesel particulate filters, the three-dimensional shape of SA stars may involve an enhancement of the number of contact points between the cake layer and the catalyst one, thus fostering the final activity. (C) 2014 Elsevier B.V. All rights reserved.