Reactions of n-butene over a nickel exchanged 13X-type zeolite

The isomerization of n-butenes has been studied in a static system using as catalysts zeolites of the 13X-type with different extents of replacement of sodium ions by nickel ions. The presence of nickel enhances the catalytic activity considerably, comparable reaction rates with the nickel-containing zeolites being observed at temperatures 200 K lower than with the parent Na13X.A striking feature of the but-1-ene reaction was the preferential formation of trans-but-2-ene, which is compatible with a reaction involving radical intermediates. Further evidence in support of a radical, rather than a carbonium ion, mechanism was obtained by observing the isomerization (a), in the presence of deuterium (when an enhancement of rate and extensive exchange were observed) and (b), in the presence of deuterium oxide (when very little exchange occurred and the reaction rate was fractionally reduced).Detailed analysis of the exchange products in the reaction of but-1-ene and deuterium over the NiX catalysts, where butane was a major product, suggested that all three butenes exchange at rates which are comparable to the rates of isomerization, and that the hydrogenation process involves a very substantial redistribution of H and D atoms between the molecules.