Catalytic activity of CoO–ZnO–MgO solid solutions for the decomposition of N2O. Role of the matrix

Abstract

The catalytic activity of CoO–ZnO–MgO solid solutions, MZCo x:y(x= 0.1–30 Zn atoms per 100 Mg atoms and y= 1–10 Co atoms per 100 Mg atoms), has been investigated for N2O decomposition in the temperature range 490–750 K at a pressure of ca. 8 kPa (60 Torr). The turnover frequency, Nion(molecules decomposed per Co ion per second), decreases with increasing zinc content (matrix effect). It also decreases with increasing cobalt concentration, more markedly at low zinc content (dilution effect). The apparent activation energy Ea increases with increasing zinc content. A comparison of the present data with earlier data on CoO–MgO, Mg1–xCoxAl2O4 and CoO–ZnO systems leads to an interpretation of the catalytic behaviour. The detrimental effect of zinc on Nion values is explained by the setting up of reaction steps which involve the formation of strongly-bound oxygen species not suitable for desorption at low temperature, and responsible for the higher Ea values.