Oxidation of Propylene over the Tin-Antimony Oxide Catalysts. II. Investigations of Physicochemical Properties of the Catalysts

Abstract

Abstract The physicochemical properties of the binary system composed of Sn and Sb oxides have been investigated. The electrical conductivity increased rapidly up to 3 atom% Sb, and subsequently decreased, little by little, as the Sb oxide content in the binary system increased. The surface area also increased rapidly up to 3 atom% Sb, and in the region exceeding this content a dilution effect due to Sb oxide was observed. The behavior of the initial rate of acrolein formation as a function of the catalyst composition was fairly similar to that of the surface area. The apparent activation energies for carbon dioxide formation at first decreased, and then became nearly constant when the Sb content of the catalysts increased. On the other hand, the activation energies for acrolein formation may be considered to be always constant, independent of the catalyst composition, at about 17 kcal/mol. The activation energies for the catalyst reduction by hydrogen were 28 kcal/mol for Sn oxide, 14 for a mixture containing 25 atom% Sb, and 30 for Sb oxide. Consequently, it has been concluded from these results that it may depend on the nature of the chemisorbed oxygen which attacks propylene whether the propylene is oxidized into acrolein or into such complete combustion products as carbon dioxide.