Polysiloxane- Derived Ceramics Containing Nanowires with Catalytically Active Tips

By direct foaming of a Pt-containing polysiloxane precursor, macroporous ceramics were generated by pyrolysis at 1400 degrees C under nitrogen or argon. The growth of nanowires was induced via a vapor-liquid-solid mechanism in which the Pt particles acted as deposition site for the decomposition gases released upon pyrolyzing the preceramic polymer. SEM, HR-SEM, TEM/EDX, and XRD investigations revealed that pyrolysis under argon atmosphere leads to short SiC nanowires of only a few micrometers length and under nitrogen atmosphere Si3N4 nanowires evolved, with length of several 10m. In both cases the tips of the nanowires mainly consisted of PtSi. In contrast to samples pyrolyzed at 600 degrees C, the components after higher temperature pyrolysis showed moderate-specific surface areas of 55-67m(2)/g. In CO oxidation experiments, a good catalytic activity was found for the Pt silicide particles, suggesting that despite their relatively large size, their location at the tips of the nanowires affords them good reactivity.