Exchange reactions of olefins with deuterium oxide on ion-exchanged X-type zeolites

Abstract

Reactions of propylene, ethylene, but-1-ene , isobutene and isobutane with D 2 O on ion-exchanged X-type zeolites have been followed by a mass spectrometric technique. Exchange was usually the main reaction but polymerization of olefins also occurred with some catalysts. All the hydrogen atoms in isobutene were exchanged at similar rates by a stepwise process but with propylene only five atoms were replaced. Exchange was complicated by simultaneous isomerization with but-1-ene. Isobutane reacted only at high temperatures but gave multiply exchanged products. The order of activity for exchange was isobutene ⪢ but-1-ene > propylene ⪢ ethylene, isobutane, and this order appeared to reflect the relative ease of formation of carbonium ions from the hydrocarbons. The character of the exchange reactions as well as the rates were in accord with mechanisms involving carbonium ion intermediates . The order of activity of the zeolites for the exchange of propylene was CeX, LaX > NiX, CuX, CoX > CaX > NaX and a correlation was found to exist between the apparent activation energy for exchange and a function of the cation charge. Reaction rates on NiX and CeX increased with increasing degree of ion-exchange and decreased with increasing amounts of D 2 O. There was evidence that in some cases the active sites were associated with acidic OH(OD) groups rather than the cations themselves.