Measurement of dispersion in silica-supported cobalt oxide catalysts

Abstract

Areas of Co 3O 4 in silica-supported cobalt oxide catalysts were measured by selective CO adsorption at 33 °C on previously vacuum-outgassed surfaces. Necessary information on the effect of outgassing temperature on CO uptake and also on the CO adsorption per unit area was obtained using unsupported Co 3O 4. An estimate was made of the number of possible adsorption sites and compared with experimental data for CO adsorption at −78 °C. Mean crystallite sizes from X-ray line-broadening were used to estimate Co 3O 4 areas in unsupported and silica-supported catalysts. The theoretical X-ray intensity and intensities from sintered samples of both types of catalyst relative to an internal standard are compared and discussed. Conditions under which agreement occurred between Co 3O 4 areas measured by gas adsorption or estimated from X-ray data are reported. Lack of agreement in the more sintered samples was ascribed to crystallite aggregation, occurring in the same temperature range for both catalyst types. This latter feature was shown to be a consequence of the structure of the supported catalysts, which were examined as ultrathin sections by electron microscopy.