2231.     MEDFORTH, S.  Promotion of Catalytic Reactions. I.  Actions of H₂ on CO and CO₂.  Jour. Chem. Soc., vol. 123, 1923, pp. 1452-1469; Chem. Abs., vol. 17, 1923, p. 3271.

        CO was 99.8% pure.  The H₂ was electrolytic and 99.9% pure.  CO₂ was used directly from cylinders.  The catalyst, Ni, was deposited from purified salts on purified pumice in the proportions 0.1 gm. of reduced Ni to 1 gm. of pumice.  The reactions involved were CO+3H₂=CH₄+H₂O and CO₂+4H₂=CH₄+2H₂O.  To provide an excess of H₂, the proportions used were H₂:CO : : 5:1 and H₂:CO₂ : : 6:1, by volume.  The maximum catalytic effect was measured by the maximum speed at which the mixed gas could be passed over the catalyst and promoter with almost complete removal of the CO or CO₂.  The reaction chamber was a straight tube fused to a preheating coil that surrounded it.  The several promoters associated with 0.1 gm. of Ni on 1 gm. of pumice in the order of decreasing efficiency in accelerating the speed of the gaseous reactions are as follows:  Ce, Th, Be, Cr, Al, Si, Zr, Mo, and V oxides (Sn and Mg oxides and Cu and Ag produce no acceleration).  The formation of CH₄ from H₂ and CO or CO₂ probably consists in the formation of intermediate addition products of the MeOH type followed by the splitting off of H₂O.  The CH₂ resulting is immediately hydrogenated to CH₄.  Or a complex intermediate product, H₄NiCOH₂, forms and decomposes into Ni, CH₄, and H₂O.  In either case, Ni must catalyze by acting as both a hydrogenating agent and as a dehydrating agent.  It is not a good agent for the latter process.  The substances that promote its catalytic action are good dehydrating agents.  When CH₃OH+3H₂ is passed over Ni the decomposition into CO and H₂ is much more rapid that the formation of CH₄ and H₂O.  If thoria is added, the rate of formation of CH₄ is increased 14-fold.  When Fe catalyzes the interaction of CO and H₂O to form CO₂ and H₂ the most effective promoters are O carriers and hydrating agents.  This indicates that H₂ is produced through the formation of formic acid as well as by alternate oxidation and reduction.  The oxidation of a gas in a gas mantle may be considered to consist of the addition of O₂ to form an intermediate compound and its subsequent dehydration.  The catalyst should be a powerful O carrier and a strong dehydrating agent.  The promoter acts (1) by decomposing intermediate compounds formed by the catalyst, or (2) by causing substances to combine, or (3) by adsorption to increase concentration.  Promoters may act selectively.