Typical Sn-80at.%Sb mixed oxide undergoes structural reduction during the decomposition of isopropyl alcohol in the absence of gas phase oxygen, and the active phase may contain metallic tin and Sb2O3. However, in the presence of oxygen the catalyst retains its structural stability and acetone is the major product together with small amounts of CO2 and propylene. Product inhibition studies with acetone reveal that oxidation of the acetone to CO2 occurs in preference to oxidation of isopropyl alcohol. The effect of the partial pressure of isopropyl alcohol and the partial pressure of oxygen on the decomposition of isopropyl alcohol was investigated. The presence of a large excess of oxygen favours CO2 formation, whereas smaller amounts of oxygen favour acetone formation. A possible mechanism for the reaction in the presence of gas phase oxygen is proposed. © 1983.