Web Release Date: February 5,
Nanostructured Praseodymium Oxide: Preparation, Structure, and Catalytic Properties
and
Institute of Applied and Physical Chemistry, University of Bremen, Leobener Str., 28359 Bremen, Germany, and Ceramic Materials and Components, University of Bremen, Am Biologischen Garten 2/IW3, 28359 Bremen, Germany
Received: August 27, 2007
In Final Form: November 15, 2007
Abstract:
Nanostructured praseodymium oxides were successfully prepared via four different methods: two traditional
methods (calcination of praseodymium nitrate and sol-gel method with propylene oxide) and two more
sophisticated, modern techniques (citrate method and modified Pechini method). Powder X-ray diffraction
revealed that all synthesis methods led to praseodymium oxide Pr6O11 with cubic fluorite-like structure. The
temperature necessary for the formation of the crystalline oxide phase, however, was dependent on the method
and synthesis parameters. The size of the nanocrystalline domains was in the range of some 10 nm in all
cases. The catalytic properties of the nanostructured oxides were studied choosing CO oxidation as a first test
reaction. According to infrared spectroscopy, the surface of all samples was covered with monodentate carbonate
species after the synthesis. After exposure to CO, two types of bidentate carbonates were observed on the
oxide surface, and under the feed of both CO and O2, carbon dioxide was observed by IR spectroscopy as
product in the gas phase at temperatures from 300 
C on. The activity with respect to CO oxidation was
further investigated in a catalytic test reactor. The maximum conversion of CO was reached at ~550 C, and
it was ~95-96% independent of the synthesis method. At moderate temperatures (~350-500 C), the activities
of the catalysts prepared in the present work were dependent on the synthesis method and synthesis parameters,
only to a small extent, but all of them were more active than commercial Pr6O11. The differences between
the various samples prepared in this study can be explained by an influence of the synthesis on the oxygen ion mobility. Mechanistically, the results of our work suggest that CO oxidation occurs through the
adsorption of CO as a bidentate carbonate, which is then transformed into a monodentate carbonate finally
desorbing as CO2.
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