Oxygen buffering capacity (OBC) of praseodymium-modified CeO2: influence of the Pr distribution in the ceria host lattice

This work reports on the redox behaviour of different ceria-praseodymia mix ed oxides with two different chemical compositions (Ce/Pr molar ratios of 4 :1 and 9:1), The samples consist of bulk oxides and ceria-supported samples with varying mixed oxide loading (equivalent to 7 or 12 mixed oxide layers ). As revealed by x-ray diffraction and high-resolution electron microscopy , the samples consist of homogeneous fluorite-like mixed oxides. Their redo x properties were characterized by means of the oxygen buffering capacity ( OBC) technique, which quantitatively evaluates the capacity of the samples for attenuating fast oscillations of the oxygen partial pressure in the He stream flowing through the sample. These oscillations are induced by inject ing with a high frequency pulses of oxygen into the inert gas stream. Altho ugh the XPS analyses performed on both a bulk and a supported sample showed Ce/Pr molar ratios very close to each other, the bulk mixed oxide exhibits significantly better OBC values. Also remarkable is that an ageing treatme nt at 1223 K improves the OBC response of the supported mixed oxides. In ac cordance with the XPS data, the enhancement of their redox properties runs parallel to an increase in the Ce/Pr surface ratio. These results are discu ssed in terms of the role played by the depth profile distribution of Pr in the different oxide samples. Copyright (C) 2000 John Wiley & Sons, Ltd.