Surface Technology, 19 (1983) 225 - 232 225 STUDIES OF THE STRUCTURAL STABILITY OF Sn-Sb MIXED OXIDE IN THE DECOMPOSITION OF ISOPROPYL ALCOHOL S. CHOKKALINGAM, B. VISWANATHAN and T. K. VARADARAJAN Department of Chemistry, Indian Institute of Technology, Madras 600036 (India) (Received January 28, 1983) Summary 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 Sb:O3. However, in the presence of oxygen the catalyst retains its structural stability and acetone is the major product together with small amounts of CO: 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 pres- sure of oxygen on the decomposition of isopropyl alcohol was investigated. The presence of a large excess of oxygen favours CO: formation, whereas smaller amounts of oxygen favour acetone formation. A possible mechanism for the reaction in the presence of gas phase oxygen is proposed. 1. Introduction Mixed oxides of tin and antimony are good catalysts for selective oxida- tion and ammoxidation of olefins [1 - 5]. Most workers [6 - 8] have stated that the formation of a solid solution of Sb s+ in SnO 2 is an important factor in the catalytic behaviour of these materials. According to the reports of Boudeville et al. [9], the selectivity for acrolein in propylene oxidation in- creases when the amount of antimony at the surface is increased; this occurs when the antimony concentration is enhanced or when the calcination tem- perature is increased. According to Boudeville et al., the active phase is Sb:O4 lying at the surface of a solid solution of antimony(V) in SnO:. The specific activity for the formation of butadiene from 1-butene has been related by Herniman et al. [10] to the concentration of antimony cations at the surface. The active sites for the formation of butadiene have been identified by Herniman et al. as isolated antimony cations surrounded entirely by tin ions as nearest neighbours. The selectivity for butadiene for- mation from 1-butene has been found to increase with increases in the antimony content in Sn-Sb oxide catalysts [11]. Christie et al. [12] have 0376-4583/83/$3.00 © Elsevier Sequoia/Printed in The Nett~erlands