In-situ Investigation of Model Multi component Catalyst Systems

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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.