Carbon monoxide oxidation kinetics on zinc oxide

Abstract

The oxidation of carbon monoxide on zinc oxide obeys first-order kinetics for CO and zero-order kinetics for O₂ with an activation energy of 104 J mol^–1 at temperatures in the range 190–250 °C. The apparent kinetics have been characterised as the sum of two different reaction paths (I and II), using the transient response method. The detailed kinetic structures of reaction paths I and II have been presented and compared using transient response techniques. For path I, the proposed model is the surface reaction of gaseous CO with O^– followed by the rapid desorption of CO₂ formed. Path II is controlled by both the surface reaction of gaseous CO with neutral atomic oxygen species and the desorption of CO₂ formed. The turnover frequency is calculated to be (6.0–150)× 10^–3 s^–1 for path I and (2.4–6.8)× 10^–3 s^–1 for path II. The former becomes much larger than the latter with increasing temperature. The experimental transient response curves are modelled according to the two mechanisms using the kinetic parameters evaluated.