Use of pulsed reduction to estimate the active surface of supported metal oxides

Abstract

Areas of Co3O4 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 Co3O4. 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 Co3O4 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 Co3O4 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.