2122. LITKENHOUS, E. E., AND MANN, C. A. Hydrogenation of Nickel Carbonyl. Ind. Eng. Chem., vol. 29, 1937, pp. 934-938; Brennstoff-Chem., vol. 18, 1937, p. 468; Chem. Abs., vol. 31, 1937, p. 6830.

According to the opinion of various investigators, Ni(CO)₄ is the intermediate product in the hydrogenation of CO over Ni as catalyst. In order to explain this reaction mechanism and to determine the equilibrium of the ensuing reaction, Ni(CO)₄ was reacted with H₂ in the ratio of 1:4. The tests were performed 25°-400° and 1-75 atm. in a Ni tube 61 cm. long. The end gas was analyzed; and, on the basis of the analysis, the equilibrium constants were determined and compared with the data in the literature; at 1 atm. Ni(CO)₄ is stable at about 100°, but shortly above, it decomposes completely into Ni and 4 CO. Above 200° the formation of H₂O, CH₄, and CO₂ begins. At 250°, 58-60% of the end gas consists of H₂O, which then decreases with further rise in temperature. Likewise CH₄ and CO₂ are at a maximum at about 350° with 20% of the end gas. The diagrams of 5-75 atm. are basically the same as at 1 atm. except that the stable limit of Ni(CO)₄ with rising pressure varies at higher temperatures. For example, at 75 atm. Ni(CO)₄ is stable up to about 220°. In contrast, an increase in pressure up to 75 atm. is virtually without influence above 250° on the composition; H₂O, CH₄, and CO₂ maintain almost the same ratio. A fairly large amount of C deposits in the reaction tube but disappears with rising temperature. The end products CO₂, CH₄, and H₂O obtained in the hydrogenation of Ni(CO)₄ are identical with those that Sabatier and Senderens found in the hydrogenation of CO. It is seen that the reaction 2C+2H₂O→CO₂+CH₄ gave constant values over the whole reaction range, whereas other possible reactions did not. The reaction can, naturally, first occur whenever C and H₂O have formed, which occurs at 250°. Normally free C does not react with H₂O at 250°, yet the reaction sets in in the presence of the Ni formed from the Ni(CO)₄.