695.    DE PAUW, F., AND JUNGERS, J. C.  [Kinetics of Hydrogenation of Acetylene and Nickel.]  Bull. Soc. Chim. Belg., vol. 57, 1948, pp. 618-630; Chem. Abs., vol. 44, 1950, p. 915.

     Hydrogenation of C₂H₂ (I) to C₂H₄ (II) or C₂H₆ was observed in a static system by means of pressure drops.  Catalyst (A) was prepared by reducing NiCO₃ precipitated on kieselguhr; (B) was prepared by reducing oxide from the calcination of Ni(NO₃)₂ at 350°.  With (A) and equimolar H₂ and (I) there was no reaction at 29°-100°, but if H₂ was admitted first, there was rapid reaction.  With equimolar H₂ and (II) there was reaction.  It was concluded that (I) by forming polymers poisoned the catalyst.  Using the less active catalyst (B) tempered by heating in a H₂+(I) mixture at 300°, and an excess of H₂ over (I) (ratios 2-20), it was possible to make kinetic experiments.  The catalyst was periodically regenerated with H₂ at 300°.  At 29°-30°, an initial reaction of steady rate continued until about 1 mol. of H₂ was used per mol. of (I); the rate then increased.  For the initial period, rate =k(H₂)/(I)^1/2.  The reaction was faster for D₂ than for H₂.  The activation energy (16°-57°) for (I) hydrogenation was 14 kg.-cal.; for (II) it was 10 kg.-cal.  Results are explained by strong adsorption of (I), which inhibits hydrogenation of (II) as long as (I) is present.  The rate laws are fitted by means of Langmuir adsorption formulas.  The adsorption coefficient of (I) is estimated to be 100 times that of H₂ at 30°, whereas that of D₂ is about 1.5 times that of H₂.

     DERRIG, M. J.  See abs. 3599.