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Role of Vapor Phase Processes on the Sintering of Diesel Oxidation Catalysts

机译：气相过程在柴油氧化催化剂烧结中的作用

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摘要

This work provides a fundamental understanding on the vapor phase processes that govern the sintering of supported nanoparticles in relation to the diesel oxidation catalyst (DOC). Sintering is a deactivation process that affects this catalyst significantly, and many other catalyst systems. Therefore, it is important to understand the sintering mechanisms in order to improve the long term catalytic reactivity.;Pt is an active catalyst in the DOC but it sinters via Ostwald ripening to form large particles under the accelerated aging conditions (800 °C) recommended by the Department of Energy (DOE). At 800 °C in the presence of oxygen, Pt forms PtO2 with a high vapor pressure. Therefore, vapor phase ripening via transport of PtO2 is significant under these conditions and leads to the growth of large Pt nanoparticles. It is well known that adding Pd improves the durability of Pt in DOCs and that the support influences the rate of Pt sintering. However, there is no clear consensus in the literature for the responsible mechanisms. In conventional powder catalysts, it is impossible to study the effect of Pd and the support on the vapor pressure of PtO2 because the pores trap the volatilized metal. In this study, an open system such as planar model catalysts were utilized to gain mechanistic insights and to directly measure the vapor pressure of PtO2.;With the use of model catalysts, it was found that the mechanism by which Pd improves the durability of Pt is two-fold: (1) Pd lowers the vapor pressure of PtO2 and (2) PdO is regenerated by the emission of Pt from Pt-Pd nanoparticles and serves as trapping sites for mobile Pt species. The trapping effect is enhanced when there is excess PdO. Lastly, model catalysts allowed for studying the role of the support on the sintering of Pt. Three supports were investigated: La-Al2O3, MgAl2O 4, and polyhedral CeO2. By depositing thin films of powder onto planar model TEM grids, it was possible to measure the vapor pressure of PtO2 and relate it to the rate of sintering.;The last study in this dissertation was performed at General Motors Global Research and Development at the Chemical and Materials Systems Lab. The work provides a fundamental study on the kinetics of propane oxidation over Pd/La-Al2O3 catalysts. The work aims to develop low temperature catalysts for hydrocarbon oxidation that will meet the 150 °C challenge as proposed by the DOE.
机译：这项工作提供了对气相过程的基本理解，该过程控制了与柴油机氧化催化剂（DOC）相关的负载型纳米颗粒的烧结。烧结是一种失活过程，会严重影响该催化剂以及许多其他催化剂体系。因此，了解烧结机理对于提高长期催化反应性很重要。; Pt是DOC中的活性催化剂，但它通过奥斯特瓦尔德熟化烧结而形成，在加速老化条件下（800°C）形成大颗粒由能源部（DOE）提供。在氧气存在下于800°C时，Pt会形成高蒸气压的PtO2。因此，在这些条件下，通过PtO2传输而进行的气相成熟非常重要，并且会导致大的Pt纳米颗粒的生长。众所周知，添加Pd可以提高DOC中Pt的耐久性，并且载体会影响Pt的烧结速度。但是，文献中对于负责任的机制尚无明确共识。在传统的粉末催化剂中，由于孔会捕获挥发的金属，因此无法研究Pd和载体对PtO2蒸气压的影响。在这项研究中，利用开放式系统（例如平面模型催化剂）来获得机理上的见解并直接测量PtO2的蒸气压。；通过使用模型催化剂，人们发现Pd改善Pt耐久性的机理有两个方面：（1）Pd降低了PtO2的蒸气压，并且（2）PdO通过从Pt-Pd纳米颗粒中释放Pt来再生，并用作移动Pt物种的捕获位点。当PdO过量时，捕集效果会增强。最后，模型催化剂可用于研究载体在Pt烧结中的作用。研究了三种载体：La-Al2O3，MgAl2O4和多面体CeO2。通过将粉末薄膜沉积到平面模型TEM栅格上，可以测量PtO2的蒸气压并将其与烧结速率相关。;本论文的最后研究是在通用汽车全球研究与开发中心进行的。和材料系统实验室。这项工作提供了有关在Pd / La-Al2O3催化剂上丙烷氧化动力学的基础研究。该工作旨在开发用于碳氢化合物氧化的低温催化剂，该催化剂将满足能源部提出的150°C的挑战。

著录项

  • 作者

    Carrillo, Cristhian.;

  • 作者单位

    The University of New Mexico.;

  • 授予单位 The University of New Mexico.;
  • 学科 Chemical engineering.
  • 学位 Ph.D.
  • 年度 2017
  • 页码 149 p.
  • 总页数 149
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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