Abstract
X-ray absorption spectroscopy, x-ray photoelectron spectroscopy, analytical electron microscopy, and x-ray diffraction were utilized to characterize Co{sub 3}O{sub 4} and Co supported on small (Co/SiO{sub 2}-62) and large (Co/SiO{sub 2}-923) pore size silica. These techniques are complementary and together provided a consistent, detailed description of the geometric structure and oxidation state of the catalysts. Co{sub 3}O{sub 4} was the only Co species detected after calcination of all three samples at 450{degree}C. For bulk Co{sub 3}O{sub 4} the particles were octahedrally shaped and 1-5 {mu}m in size. On SiO{sub 2}-62 the Co{sub 3}O{sub 4} particles were 100-300 {angstrom} in size and clustered together in 0.1-1-{mu}m aggregates. On SiO{sub 2}-923 the Co{sub 3}O{sub 4} particles were less than 60 {angstrom} in size. Both of these supported catalysts were prepared by calcination of a highly dispersed, uniformly distributed cobalt nitrate species present on the silica supports. The calcination process caused both the aggregation of the Co into larger Co{sub 3}O{sub 4} particles and the migration of the Co to the outer surface of the silica particles.
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