Hydrogenation, adsorbed hydrocarbons propene

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. 

In 1954 R. P. Eischens, W. A. Pliskin, and S. A. Francis (5) of the Texaco Research Center in New York published the first infrared spectra of chemisorbed species, namely of carbon monoxide adsorbed on the silica-supported finely divided metal catalysts of Ni, Pd, Pt, and Cu. Also, in 1956, Pliskin and Eischens (5) were the first to obtain spectra of the hydrocarbons ethylene (ethene), acetylene (ethyne), and propene adsorbed on an oxide-supported metal catalyst, Ni/Si02. Eischens and his colleagues followed this up with further studies of chemisorbed zj-alkenes and their surface-hydrogenation products on Ni/Si02 (7). 

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. 

The heats of reduction of oxide samples can be determined by studying the adsorption of hydrogen, CO and various hydrocarbons on the fully oxidized catalysts [27, 59]. The extent of reduction of the catalyst surface can be evaluated in particular using H2. The measurement of hydrocarbon (e.g. propene, propane, acrolein, etc.) adsorption heats is complicated by the subsequent reaction of the adsorbed species or by incomplete desorption of the products [60]. 

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