A study of high temperature treated supported metal oxide catalysts

The oxidation of CO and C2H4 at 200–400 °C over two groups of supported metal oxide catalysts has been studied. The catalysts in group A were mechanical mixtures of presintered metal oxides (CuO, Co3O4, NiO, and CuCr2O4, 0.1–10% by wt) with presintered catalyst supports (α-Al2O3, γ-Al2O3, and ZrO2) and those in group B were prepared by the conventional method of impregnation of the presintered supports followed by 500 °C calcination. With the exception of Cr2O3, the catalytic activity of group A supported on α-Al2O3 or ZrO2 increased 10–200-fold after being heated at 700 °C and above for 10–30 min and reached a maximum at ~900 °C, while the catalytic activity of group B remained constant or decreased slightly with increasing heat treatment temperature. The maximum activity per total surface area of group A approached that of the corresponding pair of group B, and was dependent on the composition of the catalyst. The activity of the supported catalyst per total surface area was found to be in all cases less than the corresponding specific activity of the unsupported metal oxide. This phenomenon is discussed in terms of increased dispersion induced by the high temperature treatment. When γ-Al2O3 was used as the support the thermally induced activity was much less and usually short-lived, presumably because the rate of chemical interaction and sintering overtook the rate of thermal dispersion.