ISSN:
1572-879X
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
Notes:
Abstract The catalytic behaviours of bulk tungsten carbides differently modified by air treatments have been studied in hydrogenation (or deuteration) and double-bond isomerization of but-1-ene, in hydrogen/deuterium exchange of methylcyclopentane, as well as in hydrogen dissociation via H2/D2 exchange. Two kinds of catalyst samples have been studied. The first sample has been treated by air at moderate temperature (350°C) and the second at high temperature (700°C). It was found that, for but-1-ene reaction at temperatures varying between 30 and 100°C, but-2-enes are the main products formed, and only a small amount of hydrogenated products was detected for both catalysts. Two possible double-bond migration mechanisms by an intramolecular hydrogen migration, either with π-olefinic, π-allylic and metallacyclobutane or with π-olefinic and π-allylic species interconversions are deduced; these mechanisms occur without the participation of dissociated hydrogen or deuterium atoms. However, it has been demonstrated that the hydrogen dissociation temperature is a function of the air treatment of the bulk tungsten carbide, even if this property has no effect on the hydrogenation of but-1-ene to n-butane. Thus, in order to see the influence of oxygen modification, a more detailed study has been carried out. Starting from a bulk tungsten carbide without oxygen, several controlled oxygen additions have been made, leading to four different samples. The HD formation has been analyzed for each sample as a function of temperature.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1023/A:1019063828565
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