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Literature Abstracts
1709. KEĬER, N. P., AND ROGINSKIĬ, S. Z. [Investigation of the Heterogeneity of Active Surfaces by the Differential Isotopic Method. I. The Active Surface of Metallic Nickel and Zine Oxide.] Izvest. Akad. Nauk S.S.S.R., Otdel. Khim. Nauk, 1950, pp. 27-38; Chem. Abs., vol. 44, 1950, pp. 5690-5691.
Heterogeneity of the surface of an active Ni catalyst, prepared by compression of Ni grains of 1.0-2.0 mm. diam. (by reduction of NiO in a stream of H2 at 280°), specific surface area 1.5-2 m.3/gm., was demonstrated by experiments of consecutive adsorption, at room temperature, of H2 and of D2, or 1st of D2, then of H2, and thermal conductivity analysis of the gas given up in fractions on desorption at increasing temperatures. Before the adsorption experiments, 1.05-gm. samples of the catalyst were outgassed at up to 450° under 10-5 mm. Hg, reduced once more with H2 at 450° and again outgassed at 530°. Between the 2 adsorptions, the catalyst was evacuated 1.5 min. to 10-5 mm. Hg, then the 2d gas was admitted. Data for a typical run are: 1st adsorption, D2 under 1.48 mm. Hg, amount adsorbed in 9 min. at room temperature, 0.095 cc. (S.T.P.); after short evacuation, 2d adsorption, H2 under 3.08 mm. Hg, amount adsorbed in 9 min. at room temperature, 0.04 cc., followed by 1.5 min. evacuation, the % of D2 and of H2, respectively, in the gas desorbed; at room temperature, 5 and 95; at 2°-65°, 0 and 100; at 170°-220°, 0 and 100; at 300°-320°, 40 and 60; at 420°-470°, 95 and 5; at 520°, 100 and 0; at 530°, 100 and 0. Consequently, the isotope adsorbed first is desorbed last. The same is observed in analogous runs with the order of the 2 adsorptions reversed; namely, 1st H2, then D2. In these experiments, the surface coverage is of the order of 5-10% of the total surface area. No specific effects owing to the chemical difference between H2 and D2 are observed. The conclusion is that active spots on the surface of Ni differ in their heats of adsorption and activation energies, and that there is no mixing of the molecules adsorbed on the surface. A gas of mixed composition is obtained only in desorption in an intermediate temperature range, which indicates limited mobility of the molecules in the adsorbed layer. On the basis of this finding, the exponential kinetic law established by Elovich and Zhabrova (abs. 814 and 815) for the rate of adsorption of H2 is rooted not in repulsive interaction between the adsorbed molecules but solely in the heterogeneity of the adsorbing surface. Analogous experiments were made with ZnO, prepared by oxidation of Zn in the electric arc, and outgassable at up to 500° without decomposition; decomposition is noticeable only above 600°. On adsorption of H2, the gas liberated in desorption at up to 500° is pure H2; reaction between H2 and ZnO takes place only above 500°, and then even under a pressure as low as 0.5 x 10-4 mm. Hg. If the 2 consecutive adsorptions are accomplished above 100°, only the gas adsorbed last is given up on heating; the isotope adsorbed first appears to have been spent. In room temperature adsorption, the 2d adsorbed gas is bound very weakly, and most of it is desorbed in the 1.5 min. evacuation at room temperature, which precedes the high-temperature desorption. Consequently, only the isotope adsorbed first is found in the gas desorbed on heating. This indicates that, under these conditions, only a very minor fraction of all active points has a high binding power for the adsorbed molecules, and these options are completely filled by the gas adsorbed first. This situation is changed when the 1st adsorption is done at 200°. Thus, the D2 adsorbed first under 6.15 mm. Hg. 50 min. at 200° followed by slow 16 hr. cooling to room temperature, the amount of D2 adsorbed was 0.2 cc. (S.T.P.); after short evacuation H2 was adsorbed under 6.65 mm. Hg. 34 min. at 115°, amount adsorbed 0.028 cc.; the composition of the gas given up on subsequent desorption at 170°-285°, 300°-325°, 395°-450°, 487°-495°, was (% D2 and H2), 15 and 85, 25 and 75, 20 and 80, 75 and 25%. Under these conditions, the gas adsorbed last is given up first, as in the case of Ni.
KEIL, W. Fat Acids With Odd Number of Carbon Atoms. V. Behavior of Branched Fat Acids in the Body. See abs. 1714.
Fat from Fatty Acids With Odd Numbers of Carbon Atoms. III. See abs. 1712.
Fats from Fatty Acids With Odd Numbers of Carbon Atoms. VI. See abs. 1716.
See abs. 1711, 1713, 1717.
KEIL, W., AND SCHILLER, G. Fats From Fatty Acids With Odd Numbers of Carbon Atoms. Addendum to III, IV, and V. See abs. 1715.