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 1952.    ---------------.  [KÖLBEL, H., AND ENGLEHARDT, F.]  [Reaction Mechanism of the Fischer-Tropsch Synthesis.  VI.  Function of Water Vapor in the Hydrogenation of Carbon Monoxide.]  Erdöl u. Kohle, vol. 3, 1950, pp. 529-533; Chem. Abs., vol. 45, 1951, p. 2177.

        This paper was presented at the 3d meeting of the Deutsche Gesellschaft für Mineralölwissenschaft und Kohlechemie, September 1950.  CO₂ formation on the Fischer-Tropsch catalysts results from a secondary reaction of CO with primarily formed H₂O vapor.  The result of this conversion reaction is important in the choice of synthesis conditions.  The effect of temperature upon the reaction has been previously determined, and now proof is made of the influence of space velocity on the conversion of CO with water vapor, especially in the presence of Fe catalyst.  The results obtained permit of predicting the CO:H₂ ratio for the synthesis and the space velocity to be chosen for obtaining satisfactory yields; they offer further some criterion for the most favorable synthesis gas composition for a given space velocity and temperature.  Determination of the speed of reaction of the CO conversion in a static system at temperatures down to 85° supposes a reaction of the first order, which may rest upon the dissolution of the adsorption complex of CO with H₂O on the catalyst surface.  By using a H₂-rich gas and space velocities of about 100, at normal pressure above 180° an oxidation of the catalyst by the water vapor formed during the synthesis occurs, in case a definite relation is maintained between the partial pressures of the CO and H₂O in the reaction gas.  Under these conditions the outer catalyst layers deteriorate through oxidation by water vapor.  The CO conversion is then to be considered not only as a troublesome side reaction, but it acts under certain conditions as a protector of the Fe catalyst against oxidation.  In the hydrocarbon synthesis on Fe catalysts under normal pressure, the space velocity must either be chosen so high and the temperature so low that neither CO conversion nor catalyst oxidation occurs or the CO content of the synthesis gas must be so high that even in the outer catalyst layers enough CO is present to react with the water vapor with satisfactory velocity.  In practice these conditions should exist in proper combination.