Hydrogenation of olefins. Part 3.—Reaction of ethylene and of propylene with deuterium over alumina-supported palladium and rhodium
The following reactions have been studied: I, C2H4+D2 over Pd/A12O3(–36 to 67°); II, C3H6+D2 over Pd/A12O3(19°C); III, C2H4+D2 over Rh/Al2O3(–18 to 110°); and IV, C3H6+D2 over Rh/Al2O3(88°C). Products obtained at low conversions have been separated by preparative G.L.C., and deutero-olefin and deuteroparaffin distributions derived by mass-spectrometric analysis. When the initial D2/olefin ratio is unity, the near-initial value of F(=∑(deutero-olefin)/(paraffins)) is 0.8 for reaction I at –16° and 2.7 for reaction III at 76°; F decreases with increasing initial D2/olefin ratio at these temperatures, and increases with increasing temperature within the ranges quoted above. Ethanes initially formed in reaction I (D2/olefin = 1, –16°) contain an average of about one D atom: virtually no HD is formed. Ethanes initially formed in reaction III (D2/olefin = 1, 76°) contain an average of 1.5 D atoms: considerable HD formation occurs. Reactions II and IV give product distributions and values of F similar to those given by reactions I and III under the same conditions.
Observed product distributions from reactions I and III have been compared with those computed from a steady-state scheme applicable to the C2H4+D2 system; the parameters giving optimum agreement indicate that ethylene desorption and reversion of ethyl radicals to adsorbed ethylene are both easy over Rh and Pd. Reaction mechanisms are discussed, and a ready “direct” atom transfer between ethyl radicals and ethylene molecules is indicated over Pd.