In-situ Investigation of Model Multi component Catalyst Systems

虽然人们正在使用催化剂来解决越来越具有挑战性的排放控制需要，但主要基于现象学和“试错”方法的催化系统的发展阻碍了进展。在这个项目中，来自麻省理工学院和拜罗伊特大学（UBT）的合作者将采用跨学科的方法，利用多种表征工具，在现实的操作条件下，实现对催化剂系统中所有组件（支撑，存储组件，贵金属）的行为和相互作用的详细了解。在此背景下，本提案侧重于基于（Ce，M）O2-6 （MIT）和BaCO3 （UBT）的模型催化剂配方，它们分别为各种催化剂概念提供氧气和NOx储存/释放能力。由贵金属、氧/氮氧化物存储和支撑材料组成的模型结构将集成为三层结构，通过蒸汽或溶液方法沉积在氧化物衬底上，允许系统控制表面积、三相边界和扩散长度。通过微球模板和喷墨印刷（MIT）可以实现表面面积和控制的中、纳米孔隙度。通过这些方法，可以控制存储材料中的氧扩散率，并隔离其对整体性能的影响。通过库仑滴定法、电子/离子电导率法、复阻抗法和晶体微天平等方法，研究了通过固溶体形成/掺杂剂修饰的存储材料的缺陷化学和氧交换性能。此外，表面敏感测量，包括功函数（MIT）， XPS和漂移（UBT），将应用于两个实验室。差动反应器研究（UBT）将提供所需的整体催化剂性能输入，而低热质量陶瓷微热板将允许在汽车尾气中经历的那种程序化的快速热漂移。在项目的最后阶段，单个组件的结果将被整合到一个更复杂的模型系统中，研究氧和NOx存储组件之间的相互作用，同时考虑到关键参数，如ceria/BaCO3比、空间分布、形态和金属负载。将开发和测试描述各种催化剂系统组分相互作用的模型。模型系统的整体电响应将是特别有趣的，不仅作为一种研究工具，而且作为一种诊断催化剂性能的手段。此次合作的一个核心内容是扩大学生和工作人员的交流，以学习新的实验和建模方法，应用各自实验室的独特设施，并从全球角度深入了解如何进行研究。更广泛的影响：在过去的三十年里，催化剂在减少90%以上的汽车排放方面发挥了核心作用，但这一进展在很大程度上受到了现象和“试错”方法的阻碍。因此，用于车载诊断应用的催化剂建模和优化的方法受到了抑制。该项目旨在更好地了解催化剂材料的性质及其与衬底和气体的相互作用。这样的理解将推动催化剂科学的发展，并提高设计催化剂的能力，以改善其功能。这也有可能影响到广泛的商业战略行业，包括石化催化裂化、蒸汽重整、标准化学品（氨、硫酸）合成和燃料电池电极，所有这些都依赖于多相催化剂。鉴于对环境的关注，这项工作非常适合有兴趣的年轻学生，并且将在麻省理工学院目前的水平上扩展为K-12学生的扩展计划。同样，该计划将用于吸引本科生参加该计划。

While catalysts are being called upon to address ever more challenging emission control needs, progress is hindered by development of catalytic systems based largely on a phenomenological, “trial-and-error” approach. In this program, the collaborators from MIT and the University of Bayreuth (UBT) will apply an interdisciplinary approach utilizing multiple characterization tools, under realistic operating conditions, to achieve a detailed knowledge of the behavior and interplay of all the components within the catalyst system (support, storage component, noble metal). In this context, the present proposal focuses on model catalyst formulations based on (Ce,M)O2-6 (MIT) and BaCO3 (UBT) which provide the oxygen and NOx storage/release capacity respectively for various catalysts concepts.Model structures composed of noble metal, oxygen/NOx storage and support materials will be integrated in three-layer arrangements featuring films deposited by vapor or solution methods onto oxide substrates allowing for systematic control of surface area, triple phase boundary and diffusion lengths. Surface area and controlled meso- and nano-porosity will be achieved by microsphere templating and ink-jet printing (MIT). By these means, oxygen diffusivity within the storage material can be controlled, and its impact on overall performance isolated. The defect chemistry and oxygen exchange properties of the storage materials, to be modified by solid solution formation/dopants, will be examined by coulometric titration, electronic/ionic conductivity, complex impedance and crystal microbalance methods. Additionally, surface sensitive measurements, including work function (MIT), XPS and DRIFT (UBT), will be applied in the two laboratories. Differential flow reactor studies (UBT) will provide needed overall catalyst performance input, while low thermal mass ceramic micro hot-plates will allow for programmed rapid thermal excursions of the type experienced in automotive exhausts. In the final stage of the project, results for the single components will be integrated into a more complex model system studying interactions between oxygen and NOx storage components, taking into account key parameters such as ceria/BaCO3 ratio, spatial distribution, morphology, and metal loading. Models describing the interactions of the various catalyst system components will be developed and tested. The overall electrical response of the model system will be of particular interest, not only as an investigative tool, but also as a means of diagnosing catalyst performance in situ. A central component of the collaboration will be extended exchanges of students and staff to learn new experimental and modeling methods, apply the unique facilities of the respective labs and provide insight into how research is approached from a global perspective.Broader Impact:Catalysts have played a central role in reducing automotive emissions by over 90% over the past three decades but progress is slowed by largely a phenomenological, “trial-and-error” approach. As a consequence, means for rationalizing the modeling and optimization of catalysts for onboard diagnosis applications has been inhibited. This project aims to obtain an improved understanding of the catalyst materials properties and their interactions with substrate and gases. Such understanding will advance the science of catalysts as well as improve the ability to engineer catalysts towards improved functionality. This has the potential for impacting, as well, a broad range of commercially strategic industries including petrochemical catalytic cracking, steam-reforming, synthesis of standard chemicals (ammonia, sulfuric acid), & fuel cell electrodes, all of which depend on heterogeneous catalysts. Given the focus on environment, this work is ideally suited for interesting young students and an outreach program for K-12 students will be expanded from present levels at MIT. Likewise, the program will be used to attract undergraduates to the program.