Deuterium reactions

Deuterium—deuterium reactions are harder to ignite and yield less energy than D—T reactions, but eventually should be the basis of fusion energy production (172). Research into the production of fusion power has been ongoing since the 1950s (173—177) (see Eusion energy). 

EPR has been observed and studied in porous carbons by numerous authors 178-182). The carbons studied have been prepared by pyrolysis of organic material such as dextrose 180), coal 181), and natural gas or oils 181,182). Porous carbons are of considerable technological importance and show catalytic activity for the ortho-parahydrogen conversion, the hydrogen-deuterium reaction, and many reactions of inorganic complex ions 156). Relationships between the characteristics of the EPR absorption and the catalytic activity of porous carbons for the o-p Hj and Hj-D reactions have been demonstrated by Turkevich and Laroche 183). 

The reactions of the n -butenes with deuterium have been studied over alumina-supported platinum and iridium [103] and palladium [124]. In general, the results obtained are similar to those discussed above for ethylene—deuterium and propene—deuterium reactions. A comparison of the deuteroalkane distributions over platinum is shown in Fig. 17. 

Modification of selectivity induced by sulfur adsorption has been widely studied (41, 90, 75) and can be evaluated by comparison of the initial toxicides (see Table VI) for different parallel reactions. As an example, sulfur on platinum does not inhibit similarly benzene hydrogenation and the exchange with deuterium reactions. The H/D exchange is less deactivated than the hydrogenation. For instance, one sulfur atom (introduced as H2S) poisons five accessible platinum atoms for benzene hydrogenation, whereas it poisons only two platinum atoms for exchange. The mechanism of selectivity modification induced by sulfur adsorption is far from being explained. 

Eley-Rideal) mechanism, one of the reactants comes directly from the fluid phase to react with the other, which is already chemisorbed. This procedure was devised to explain the kinetics of the hydrogen-deuterium reaction on certain metals (see Section 9.2), but has also been suggested for other reactions. The Mars-van Krevelen mechanism applies to oxidations catalysed by oxides that are easily reducible, and are therefore able to release their lattice oxide ions for the purpose of oxidising the other reactant they are then replaced by the dissociation of molecular oxygen. With gold catalysts supported on such oxides, it is sometimes proposed that this mechanism plays a part in the total process. 

The sequence for ethylene at 50°C. on several alumina-supported metals has been derived from a detailed analysis of the products of the ethylene-deuterium reaction (7) and is ... 

The reaction of equal pressures of 1-butene and deuterium over nickel wire at 90° (48) follows a course reminiscent of the ethylene-deuterium reaction vmder these conditions (see Fig. 6) butane-do is a substantial... 

An examination of the ethylene-deuterium reaction at the surface of a palladium thimble has been briefly reported 54) the gas diffusing through the thimble during the reaction was found to contain 10% H. Final ethane distributions from this reaction over palladium-silica and palladium-charcoal under high pressure at —78° have been reported 46). 

A preliminary study of the propylene-deuterium reaction over palladium-pumice (55) showed extensive olefin exchange the reaction has since been re-examined using palladium-alumina 31). The progress of the exchange reaction at — 20° is shown in Fig. 8, from which it appears... 

On the basis of the above facts and on the additional fact that the exchange reaction was found to be very nearly first order with respect to isobutane, the following scheme for the mechanism of the deuterium reaction was proposed ... 

The deuterium plus tritium and deuterium plus deuterium reactions are of interest in the development of controlled fusion devices for producing energy. A number of designs have been proposed for these fusion reactors, with most attention given to inertial confinement and magnetic confinement systems. 

The effect of the temperature on the course of the ethylene-deuterium reaction at half atmospheric pressure was studied at —78, —50, 0, and 110°, and the results are presented in Table II for a nickel-on-kieselguhr catalyst. It is seen that the deuterium gas is free of protium up to 0° and contained 36% hydrogen at 110°. The ethylene fraction was free of deuteroethylenes at —78 and —50° but contained appreciable amounts at 110°. A redistribution of the deuterium among the various deuteroethanes was noted at —78° and a trend toward the more heavily deuterated compounds as the temperature was raised. 

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. 

Preliminary results for the hydrogen-deuterium reaction indicate that there is no appreciable difference in the activities of a nickel catalyst following the different treatments listed above. 

For the hydrogen-deuterium reaction, the Hi and HD mass peaks are observed in the mass spectrometer. The value corresponding to po is obtained by adding one-half of the HD mass peak to the Ha mass peak. 

On the basis of these results, it does not appear that there is any difference which can be attributed to a change in density of surface defects for the hydrogen-deuterium exchange. Hence, the results indicate that the rate-controlling factor for the hydrogen-deuterium reaction is not the same as that for the hydrogen-ethylene reaction. 

The great advantage of the study of exchange reactions of isotopic molecules on catalysts is that only one molecular species is involved both as reactants and products. One is freed from the restrictions imposed with two reactants where the displacement of one reactant by another or by a reaction product must steadily be taken into consideration. The catalysts which reveal heterogeneity by desorption-readsorption studies should show the same variation in activation energy of reaction with temperature that Taylor and Smith found with zinc oxide in the hydrogen-deuterium reaction. Research in this direction is under way. 

Most studies of the methane-deuterium reaction have been performed in static systems, which do not clearly reveal changes of activity with time in a flow-system, however, films of metals in Groups 5 and 6, and nickel, increase in activity with... 

When alkene is in excess, the reaction in a constant volume system stops when the deuterium is used up, and the deuterium alkene ratio decreases continuously as the reaction proceeds. Unreacted but partially exchanged alkene remains at the end, and the deuterium number of the alkanes M is less than two, the alkane-d<, becoming a major product (see Figure 7.9 for the propene-deuterium reaction on Pt/pumice ). Contrarily when deuterium is in excess, the final alkane deuterium number is greater than two, the alkene-rfo falls to near zero, and the alkane-d2 becomes the major product (see also Figure 7.9). Similar but less complete results were seen with propene ° and ethene on a variety of supported platinum catalysts. 

TABLE 7.5. Values of Parameters Describing the Ethene-Deuterium Reaction ... 

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. ... 

The ethene-deuterium reaction has been studied over Pt( 111) between 300 and 370 ethane-di was the chief product and the mean deuterium number of... 

The propene-deuterium reaction has been examined more recently on the same surface using TPD spectroscopy the extensive results obtained are described in a lengthy paper. Above 230 K, all deuteropropenes and propanes were found,... 

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