Carbon aerogels and Cr-, Fe-, Co-, and Ni-containing carbon aerogels were o
btained by pyrolysis, at temperatures between 500 and 1800 degrees C, of th
e corresponding aerogels prepared by the sol-gel method from polymerization
of resorcinol with formaldehyde. All samples were characterized by mercury
porosimetry, nitrogen adsorption, X-ray diffraction (XRD), high-resolution
transmission electron microscopy (HRTEM), and Raman spectroscopy. Results
obtained show that carbon aerogels are, essentially, macroporous materials
that maintain large pore volumes even after pyrolysis at 1800 degrees C. Fo
r pyrolysis at temperatures higher than 1000 degrees C, the presence of the
transition metals produced graphitized areas with three-dimensional stacki
ng order, as shown by HRTEM, XRD, and Raman spectroscopy. HRTEM also showed
that the metal-carbon containing aerogels were formed by polyhedral struct
ures. Cr and Fe seem to be the best catalysts for graphitization of carbon
aerogels.