Reactions of dimethylbutenes on nickel-exchanged and zinc-exchanged 13X-type zeolites

Abstract

Reactions involving 2,2-dimethylbut-l-ene (I), 2,3-dimethylbut-l-ene (II) and 2,3-dimethylbut-2-ene (III), including isomerization and exchange with D₂ or D₂O, have been studied on zinc-exchanged and nickel-exchanged X-type zeolites. The effect of various pretreatments (with hydrogen, carbon monoxide or oxygen) was examined with NiX (21% exchanged) which, unlike the ZnX zeolites, was a catalyst for the hydrogenation of the C₆ alkenes.

The acid-catalysed isomerization of I (to II and III) occurred on both ZnX and NiX and the activity of the zeolites increased sharply with M²⁺ ion content. With ZnX(21) or NiX(21) inclusion of H₂O or D₂O (which gave exchanged products) in the reaction mixture enhanced the rate of isomerization of I, presumably by the creation of more Brønsted acidity. Hydrogenation activity was found only with NiX and was attributed to the reduction of some of the accessible Ni²⁺ ions by the alkene + hydrogen mixture to Ni⁺ or possibly Ni⁰. Treatment with carbon monoxide or oxygen demonstrated the dual-function behaviour of NiX(21), not influencing the acidic catalysis but inhibiting almost completely the hydrogenation activity.