Hydrogen/deuterium reaction with nickel

At 90° on a moderately active catalyst of nickel wire in the absence of ethylene the hydrogen-deuterium reaction is complete within 3 hrs. The presence of ethylene markedly retards the rate of this reaction as the following experiment showed 12 mm. of C2H4,9.6 mm. D2, and 10.1 mm. of H2 were contacted with the nickel wire for 4 hrs. At the end of this period, when 10% addition to the double bond took place, there were 6.1 mm. of D2,8.4 mm. H2, and 4.5 mm. HD. If equilibrium had been attained, the composition would be 4.0 mm. D2,6.0 mm. Hg, and 9.2 mm. HD, indicating that the ethylene had suppressed the equilibration of the hydrc en isotopes. 

These features are best illustrated by reference to the reaction of ethene with deuterium on various nickel catalysts °° ° and on supported platinum catalysts.On nickel there was seen the stepwise formation of al the deuterated ethenes (Figure 7.6), in consequence of which (hydrogen exchange being minimal) the deuterium number of the ethane rose progressively thus ethane-rfo was the major initial product, but all deuterated ethanes were seen, and the formation of ethane-r/e was more marked towards the end of the reaction, when most of the ethene was ethene-da (Figure 7.7). The stepwise character of the... 

There are few reports of alkene-deuterium reactions on bimetallic catalysts, but those few contain some points of interest. On very dilute solutions of nickel in copper (as foil), the only product of the reaction with ethene was ethene-di it is not clear whether the scarcity of deuterium atoms close to the presumably isolated nickels inhibits ethane formation, so that alkyl reversal is the only option, or whether (as with nickel film, see above) the exchange occurs by dissociative adsorption of the ethene. Problems also arise in the use of bimetallic powders containing copper plus either nickel, palladium or platinum. Activation energies for the exchange of propene were similar to those for the pure metals (33-43 kJ mol ) and rates were faster than for copper, but the distribution of deuterium atoms in the propene-di clearly resembled that shown by copper. It was suggested that the active centre comprised atoms of both kinds. On Cu/ZnO, the reaction of ethene with deuterium gave only ethane-d2. as hydrogens in the hydroxylated zinc oxide surface did not participate by reverse spillover. ... 

Other metals of Groups 8 to 10 have very different characteristics in respect of reactions of the butenes with hydrogen and deuterium as might be expected from the way they behave in the ethene- (and propene-) deuterium reactions, nickel, palladium, ruthenium, rhodium and osmium are able under some conditions to exhibit much higher values of r,/rfc, so that the butenes are able to achieve their equilibrium concentrations before their hydrogenation is finished. 

A last case of sonication-sensitive catalytic reactions is the hydrogen-deuterium isotope exchange observed in carbohydrates in the presence of nickel or a nickel-aluminum alloy. A good selectivity is observed, probably due to the lower temperature allowed by sonication. However, a more complex origin can be responsible for these effects, since the sonicated alloy exhibits new features such as distinct catalytic centers, and elemental redistribution within the catalyst bulk, along with more classical consequences (surface cleaning, absence of surface area... 

---