Materials World Network: In-Situ Investigation of Model Multi-Component Catalyst Systems

Massachusetts Institute Of Technology, Cambridge MA

Investigators

Abstract

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). This is a joint project between the Massachusetts Institute of Technology (MIT- USA) and the University of Bayreuth (UB- Germany). 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 on-board 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 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 young students and an outreach program for K-12 students is expanded under this program from present levels at MIT. The program is used to attract undergraduates and to provide graduate students experience working in a global scientific environment. An interdisciplinary approach is applied which utilizes 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). Model structures composed of noble metal, oxygen/NOx storage and support materials are 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 are achieved by microsphere templating and ink-jet printing (MIT). The defect chemistry and oxygen exchange properties of the storage materials, to be modified by solid solution formation/dopants, is examined by coulometric titration, electronic/ionic conductivity, complex impedance and crystal microbalance methods. Additionally, surface sensitive measurements, including work function (MIT), XPS and DRIFT (UB), are applied in the two laboratories. Differential flow reactor studies (UB) provide needed overall catalyst performance input, while low thermal mass ceramic micro hot-plates allow for programmed rapid thermal excursions of the type experienced in automotive exhausts. Models describing the interactions of the various catalyst system components are developed and tested. The electrical response of the model system is of interest as an investigative tool and as a means of diagnosing catalyst performance in situ. A central component is the extensive exchange of students and staff providing opportunities to learn new experimental and modeling methods and to gain insight into how research is approached from a global perspective.