Hydrogenation, adsorbed hydrocarbons butene

Naito et al. studied hydrogenation with use of adsorption measurements, mass spectrometry, and microwave spectroscopy for product analysis. In the room temperature deuteriation of propene, butene, and 1,3-butadiene, the main products were [ H2]-propane, [ H2]-butane, and l,2-[ H2]-but-l-ene, respectively. They showed, using mixtures of H2 and D2, that deuterium was added in the molecular form and at a rate proportional to the partial pressure of D2, as opposed to D surface coverage the reaction rates were zero order in hydrocarbon. They proposed, therefore, in contrast to the model of Dent and Kokes for ethene (but note in this case that reaction rate was 0.5 order in hydrogen pressure and proportional to ethene surface coverage), that hydrogenation proceeded by interaction of adsorbed hydrocarbon with gas-phase D2, that is by an Eley-Rideal mechanism. 

Garrone et al. (168) have shown that the sensitization of MgO to electron donation by preadsorption extends to propene, butene, and acetylene. Ultraviolet reflectance measurements show bands characteristic of the carbanions, and the protons are assumed to react with 02c to form OH c. The addition of oxygen then leads to an electron transfer from the carbanion to form 02, whereas the radical then formed can oxidize or dimerize. They suggest that in this way OJ can be formed without the need for electron transfer from the solid to form a preexisting radical. However, it is clear that the oxide surface is involved and without the presence of 0 c the reaction will not proceed. The function of the Owould be to abstract a proton from the adsorbed molecule alternatively an electron could be donated to the hydrocarbon molecule and then the 0 c would abstract a hydrogen to form OH c. 

It is not intended that the literature concerning the hydrogenation of alkenylalkynes and dialkynes shall be reviewed in detail. However, the hydrogenation of molecules as unsaturated as these provides further examples of the operation of the thermodynamic factor which are of interest. The palladium-, platinum-, and nickel-catalyzed hydrogenations of vinylacetylene (H2C=CH—C=CH) provides 1,3-butadiene as the major initial product butenes and butane are also produced (57). The product distributions are constant in liquid phase reactions until the parent hydrocarbon has been removed, showing that vinylacetylene is more strongly adsorbed than 1,3-butadiene and the butenes. The relative yields of butenes and butane resemble those obtained in 1,3-butadiene hydrogenation over these metals (see Section III, F, 6). 

---