Nickel deuterium-ethylene exchange

One of the earliest studies of the reaction of C2H4 with D2, in which a full mass spectrometric analysis of the products was performed, used a nickel wire as catalyst [115,116]. Some typical results are shown in Fig. 11. These results showed that ethylene exchange was rapid and the deutero-ethylenes are probably formed in a stepwise process in which only one deuterium atom is introduced during each residence of the ethylene molecule on the surface, that is there is a high probability of ethylene desorption from the surface. From Fig. 11(a) it can also be seen that the major initial products are ethane-d0 and ethane-d,. This is consistent with a mechanism in which hydrogen transfer occurs by the reaction... 

When deuterium and ethylene are bi-ought together in contact with a nickel catalyst, the exchange reaction... 

Hydrogen is chemisorbed on a surface partially covered with ethylene and reacts rapidly with the ethylene at room temperature. This is not consistent with observations that hydrogen-deuterium exchange on nickel is strongly inhibited by the presence of chemisorbed ethylene. The latter effect may be due to fragmentation of ethylene which occurs only at higher temperatures. 

According to Matsusita (46) the. adsorption of ethylene on reduced nickel proceeds in proportion to the 0.44th power of the equilibrium pressure on a sparsely covered surface as shown in Fig. 6. This may indicate dissociative adsorption of the ethylene molecule into two parts although the deviation from the square root type of adsorption (0.5th power) remains unexplained. The absence of the exchange reaction of deuterium... 

The log—log plot of the adsorption isotherm, which can possibly be correlated to the pressure-dependency of the catalytic reaction rate, is very flat. The adsorption of ethylene on nickel increases only by 10% for an increase of the equilibrium pressure by a factor of 10, although the surface is still far from being covered by a monolayer. The work of Laidler et al. (3), who studied the ammonia-deuterium exchange reaction on a promoted iron catalyst by means of the microwave method, also throws doubt on the zero-order kinetics with respect to observations made by Farkas (4). 

An interesting differentiation between reactions was observed on nickel. The hydrogen-deuterium exchange activity was not affected by a bombardment that altered the rate of ethylene hydrogenation by a factor of 100 (44). Evidently the defects responsible for the latter are... 

A remarkable effect was observed when sintered iron films were used. The multiple exchange process disappears and a normal distribution is obtained (see Pig. 7b). The use of sintered films also enabled a course of reaction to be followed (cyclohexene at 0°, cyclopentene at —35°) stepwise olefin exchange was observed, slightly more marked with cyclopentene than with cyclohexene, and the results bear a marked resemblance to those shown for the reactions of ethylene and of 1-butene with deuterium over nickel in Figs. 5 and 6. Sintering also removes the ability of iron films to catalyze the disproportionation of cyclohexene to cyclohexene and benzene, and for this reason it was... 

Complete analyses of the various deutero-ethylenes and deutero-ethanes were first obtained by Turkevich et at. (4), using a nickel wire, and this type of information has since been reported by Wilson et al. 5) for a bulk nickel catalyst and by Kemball 6) for a series of evaporated metallic films. In all cases, the ethanes produced range over the complete spectrum from do-ethane to do-ethane, and Kemball showed that it is possible to correlate the nature and the amount of the deutero-ethylenes formed over metallic films with the distribution of deuterium in the ethanes. Although the detailed mechanisms of the exchange and deuteration of ethylene are still the subject of controversy, it is clear that both are closely related and both involve the half-hydrogenated state, i.e., the adsorbed ethyl radical, as an intermediate. The main objective of the present research was to extend such studies to the benzene-deuterium system. 

Effects of Radiation Quenching, Ion-Bombardment, and Annealing on Catalytic Activity of Pure Nickel and Platinum Surfaces. II. Hydrogenation of Ethylene (continued). Hydrogen-Deuterium Exchange f... 

G.H. Twigg and E.K. Rideal. The Exchange Reaction between Ethylene and Deuterium on a Nickel Catalyst. Proc. R. Soc. London A171 55 (1939). 

The classical researches of Sabatier and his colleagues revealed the wide applicability of metallic nickel as a catalyst for the hydrogenation of the olefinic double bond. Many years passed before the mechanism of this type of conversion was disclosed this resulted from the discovery of deuterium, which made possible a study of the exchange reactions of ethylene. Because of its important bearing on geometrical problems, a brief account of this work must be included. 

J. Horiuti and M. Polanyi (78) discovered that platinum black catalyzed the exchange of atoms between deuterium gas and liquid water. A. and L. Farkas and E. K. Rideal (79) discovered the exchange between deuterium and ethylene catalyzed by nickel, to be discussed in section VIII. 

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