INFLUENCE OF HYDROGEN AND OF REACTION TEMPERATURE ON THE MECHANISM OFN-BUTANE ISOMERIZATION OVER SULFATED ZIRCONIA

Over HMOR zeolites, hydrogen inhibits n-butane isomerization which occ urs through a bimolecular pathway and has practically no effect on n-h exane isomerization, of which the reaction mechanism is intramolecular . The large inhibiting effect found with butane isomerization is certa inly related to the demanding character of the bimolecular process: tw o sec-butyl carbenium ions are necessary for the alkylation step. Hydr ogen could react with carbenium ions limiting their concentration. Ove r sulfated zirconia hydrogen has also an inhibiting effect on n-butane isomerization, this effect being particularly pronounced at low tempe rature, and has no effect on n-hexane isomerization. It is suggested t hat the differences in the butane isomerization mechanisms proposed in the literature in the case of sulfated zirconia are mainly due to the ''diluent'' gas used (nitrogen and hydrogen) and for a small part to the reaction temperature.