A study of high temperature treated supported metal oxide catalysts

Abstract

The oxidation of CO and C 2H 4 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, Co 3O 4, NiO, and CuCr 2O 4, 0.1–10% by wt) with presintered catalyst supports (α-Al 2O 3, γ-Al 2O 3, and ZrO 2) 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 Cr 2O 3, the catalytic activity of group A supported on α-Al 2O 3 or ZrO 2 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-Al 2O 3 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.