Abstract
Bulk platinum has been known to be chemically inert, but shows remarkably high activity as a catalyst when finely dispersed as nano particles (10 nm) in ceramic substrates. In order to understand this mechanism, we have studied the effect of a reducing environment on the structure, morphology, and distribution of these Pt nano particles as well as of oxide support in gadolinium-doped ceria catalysts by transmission electron microscopy (TEM) and x-ray photoelectron spectroscopy (XPS) methods. In fresh catalysts prepared by calcinations, the Pt nano particles were found to be crystalline with many of them twinned and distributed randomly in the microstructure of crystalline ceria support. The size of the Pt nano particles ranged between 20 and 50 nm. A special feature found in these catalysts is that no constituting Pt particle is partially or fully embedded in the ceria grain. Upon reduction with hydrogen gas at high temperatures, both Pt and ceria crystals showed evidence of crystalline defects. The Pt nano particles in reduced catalysts appeared similar in size and shape to those observed in the fresh catalysts, and they resided on the surface of the ceria crystal. The results are discussed in relation to their expected catalytic activity in autothermal reforming of iso-octane.
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