AN EXAMINATION OF PRASEODYMIA AS AN OXYGEN-STORAGE COMPONENT IN 3-WAYCATALYSTS

The redox properties of praseodymia have been compared to those of cer ia using temperature-programmed desorption (TPD) of O-2 from films pre pared by vapor deposition onto an alpha-Al2O3(0001) support, in order to assess the potential for praseodymia as an oxygen-storage component in three-way catalysts. Desorption of O-2 was observed between 700 an d 1000 K, and diffraction measurements confirmed that the films change from Pr6O11 to Pr2O3 in this temperature range. However, once reduced , the films could not be reoxidized by exposures to O-2 in the vacuum system. Evidence was found for oxygen transfer from Pr6O11 to supporte d Ph particles. Following CO adsorption on Ph particles deposited onto Pr6O11 film, significant amounts of CO2 were observed in TPD until th e film was completely reduced to Pr2O3 Following deposition of Rh part icles onto Pr6O11. the oxygen desorption curves became identical to th ose normally observed for Ph. These results are compared with similar measurements performed on ceria films and the implications for automot ive, emission-control catalysis are discussed.