Mn Oxide Catalysts for Fischer-TroDsch-Synthesis etc. We thank Professors B. E. Conway and J. O M . Bockris and Drs. V. Jovancicevic and A. Gochev for valuable discussions and criticisms of the manuscript. [12] References B. E. Conway, D. J. MacKinnon, and B. V. Tilak, Trans. Faraday Soc. 66, 1203 (1970). J. O'M. Bockris, R. Parsons, and H. Rosenberg, Trans. Faraday SOC. 47, 766 (1951). J. O'M. Bockris and R. Parsons, Trans. Faraday SOC. 45, 916 (1 949). B. E. Conway and M. Salomon, J. Chem. Phys. 41, 3169 (1 964). H. P. Stout, Trans. Faraday SOC. 41, 64 (1945).Iron/manganese oxides often used as catalysts for the Fischer-Tropsch (FT) hydrogenation of CO have been characterized by their adsorption properties. N2 physisorption was carried out at 77 K and CO chemisorption at 194 K in a vacuum microbalance. Precipitated solids with compositions ranging from pure iron oxide to pure manganese oxide were studied after calcination and reduction. The results indicate a correlation between the fraction of metallic iron in the surface, the irreversible chemisorption of CO at 194 K and the initial activity for FT synthesis.