Study of Low-Temperature Active Rare-Earth Oxide Catalysts for Automotive Exhaust Clean-up

Recently, there is a large body of literature on improving low-temperature reducibility (catalytic activity) of ceria zirconia (CeO2-ZrO2) achieved by rational thermal redox treatments. This is driven by lowering the light-off temperature of catalysts, improving the pollutant conversion efficiency during automotive engine cold start, reducing the aging processes of catalysts, and easing thermal management. Our preliminary work suggests that simply making a solid solution of ceria and zirconia (currently used material for automotive three-way catalytic converter) will not give material with the highest activity (e.g. low-temperature reducibility). There is still considerable uncertainty about the possible detailed mechanism by which ZrO2 enhances the oxygen storage and release capacity for CeO2. Such mechanisms include facilitating oxygen vacancy formation, lattice distortion induced by cubic and tetragonal transformation, forming easily reducible intermediate phases, and local strain by lattice mismatch, etc. In this proposal, we plan to carry out a detailed structure, chemistry, and properties relationship study in low-temperature reducible CeO2-ZrO2 solid solution oxides to identify the nanostructural and nanochemical factors that control the reduction and oxidation rates in CeO2-ZrO2 nanoparticles including particle size and shape, structure, average composition and composition profiles. To measure the overall properties of the materials some commonly used techniques will employed including: * X-ray Diffraction (XRD) * Surface Area Measurement (BET) * Thermogravimetric Analysis (TGA) of Redox Processes * Temperature Programmed Reduction and Oxidation (TPR and TPO) * X-ray Photoelectron Spectroscopy (XPS) * Raman Spectroscopy. The project will synthesize a series of well-controlled model systems covering a wide range of compositions using a spray freezing technique. A systematic thermal redox treatment of these nanopowders will be employed to improve their low-temperature reducibility. Powder X-ray diffraction will be performed to determine the overall crystallinity and structure of materials. Raman spectroscopy will be applied to determine the coordination symmetry of cations and unit cell distortion in CeO2-ZrO2 solid solution oxides. X-ray photoelectron spectroscopy (XPS) will be used to obtain further information about the average valence/oxidation state of the elements and surface composition of the CeO2-ZrO2 solid solution oxides by inspecting the spectral line shape and the intensities of the Ce 3d core-level electrons. The redox property of CeO2-ZrO2 oxides and metal supported catalysts will be characterized using temperature programmed reduction (TPR) and thermogravimetric analysis (TGA), which will provide information about the ability of oxides to generate oxygen vacancies and transfer the oxygen onto the metal particles. Altogether, this information will give the average properties and redox behavior of the materials. The overall properties will be correlated with our detailed nanoscale (or atomic level) electron microscopy and spectroscopy study to identify the structure and chemistry of individual nanoparticles at the atomic level using transmission electron microscopy (TEM) related techniques: * High Resolution Transmission Electron Microscopy (HRTEM) * Scanning Transmission Electron Microscopy (STEM) * Electron Energy Loss Spectroscopy (EELS) * Energy Dispersive X-ray Spectroscopy (EDX) We propose to employ the combination of macroscopic and microscopic techniques to answer some of the fundamental questions in ceria zirconia system with low-temperature catalytic activity. Our long-term goal is to identify the nano-characteristics of the most active and stable particles and develop synthesis methods to maximize the fraction of this phase.

Language

  • English

Project

  • Status: Completed
  • Funding: $99998.00
  • Contract Numbers:

    DTRT06-G-0041

  • Sponsor Organizations:

    Youngstown State University, Ohio

    Center for Transportation & Materials Engineering
    One University Plaza, Moser Hall
    Youngstown, OH  United States  44555
  • Project Managers:

    Esenwein, Joann

  • Performing Organizations:

    Youngstown State University, Ohio

    Center for Transportation & Materials Engineering
    One University Plaza, Moser Hall
    Youngstown, OH  United States  44555
  • Principal Investigators:

    Wang, Ruigang

  • Start Date: 20110501
  • Expected Completion Date: 0
  • Actual Completion Date: 20120501
  • Source Data: RiP Project 28199

Subject/Index Terms

Filing Info

  • Accession Number: 01514360
  • Record Type: Research project
  • Source Agency: Youngstown State University Center for Transportation and Materials Engineering
  • Contract Numbers: DTRT06-G-0041
  • Files: UTC, RiP
  • Created Date: Feb 15 2014 1:00AM