Paste is formed consisting of ferrous carbonate, a compound of a catalytic metal of atomic number 22-30, excluding Fe, capable of yielding the oxide on calcination, a compound of an alkali metal capable of yielding the oxide on calcination, and H2O. The proportions of the product after calcination shall be, 2-30% oxide of the catalytic metal, up to 28% oxide of the alkali metal, and not less than 70% Fe oxide, percentages based on total weight of final product. H2O shall be present in proportion suitable for extrusion. The paste is extruded, shaped, and sized. The catalyst is heated to 110°-150° C. to remove H2O and then calcined at 900°-950° C. for 2-6 hr. 2 United States patents cited.