Hydrothermally Stable Ceria/Alumina Supports for Exhaust Emission Control

Hien  Pham, University of New Mexico

Hydrothermally Stable Ceria/Alumina Supports for Exhaust Emission Control

Hien N. Pham1, Andrew De La Riva1, Eric J. Peterson1, Konstantin Khivantsev2, Xiaohong Li2, Dong Jiang3, Yong Wang2,3, Abhaya K. Datye1

  1. Department of Chemical and Biological Engineering, and Center for Microengineered Materials, University of New Mexico, Albuquerque, NM 87131
  2. Institute for Integrated Catalysis, Pacific Northwest National Laboratory, Richland, WA 99352, USA
  3. Department of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA 99164, USA

There is an industry-wide need to maximize the activity of three-way catalysts (TWCs) while drastically reducing platinum group metal (PGM) content (Pt, Pd and Rh).  TWCs need to perform effectively at low temperatures for cold-start (the 150 °C challenge) but they must also be able to survive accelerated aging at temperatures up to 1000 °C under hydrothermal conditions (e.g., 10% steam).  As single phase oxides, ceria or alumina supports are not hydrothermally stable in air/10% steam at accelerated aging conditions, but composite ceria-alumina supports possess excellent hydrothermal stability.  We have discovered that ceria-alumina supports consist of two forms of ceria, crystalline nanoparticles of ceria located on the alumina surface and also atomically dispersed cerium cations. It is well known that atomically dispersed lanthanum stabilizes alumina and prevents loss of surface area, the role of atomically dispersed Ce has not been investigated.

Here we report on a study of ceria-alumina supports that were characterized via AC-STEM, XRD and BET surface area measurement to determine the relative amounts of the two ceria phases (atomically dispersed ceria and crystalline ceria nanoparticles).  These supports were aged hydrothermally at temperatures up to 1000 C in 10% steam and were tested for their ability to provide sites for trapping single atoms of Pt and for improving thermal stability of the Pt.  The reactivity of the Pt for CO oxidation was used as a probe to understand the role of the various forms of ceria on maintaining PGM dispersion and for achieving low temperature reactivity.  Another focus of this study was on understanding the nature of the sites on alumina that allow Ce to be atomically dispersed and how the dispersed Ce in turn helps in improving hydrothermal stability of the alumina support.  This work provides important clues for the design of high temperature stable ceria/alumina composite supports for exhaust emission control.

The authors gratefully acknowledge the U.S. Department of Energy (DOE), Energy Efficiency and Renewable Energy (EERE), Vehicle Technologies Office for the financial support of this work.