SO2-INDUCED ISOMERIZATION OF 2-BUTENE OVER CATION-EXCHANGED X ZEOLITES

SO2 adsorbed on alkali-, alkaline earth-, and rare earth-exchanged X zeolites induces the isomerizations of cis-2-butene. Different kinetic behavior between the two isomerizations (cis-trans isomerization and double-bond migration) has suggested that the two isomerizations proceed via different mechanisms. The geometrical isomerization has been interpreted by means of the previously suggested mechanism where the cis-trans conversion is accompanied by the cooligomerization of SO2 and 2-butene. Activities of the zeolites for this reaction have been correlated to the polarizing power of the exchangeable cation of the zeolites, suggesting that the initiation of the cooligomerization (and accordingly the geometrical isomerization) takes place by means of a polarization of the charge-transfer complex, formed from SO2 and 2-butene, under the influence of metal cations. It is inferred that the SO2-induced double-bond migration observed on alkaline-earth and rare-earth zeolites is caused by the generation of new acidic OH groups through the reaction of SO2 with basic OH groups bonded to metal cations. © 1979.