ISOMERIZATION OF N-HEXANE ON PLATINUM DEALUMINATED MORDENITE CATALYSTS .2. KINETIC-STUDY

A kinetic study of n-hexane isomerization was carried out under low pressure (1 bar, p(H2)/p(n-hexane) from 1-6) and under high pressure (10-35 bar, p(H2)/p(n-hexane) from 4-16) on a series of 0.3 wt.-% Pt-HMOR samples differing in their Si/Al ratio (7-68). Under high pressure the reaction orders with respect to hydrogen and n-hexane were equal to about -0.8 and 0.8, respectively, on catalysts with low or high Si/Al ratios. Under low pressure hydrogen also had an inhibiting effect on the sample with the highest Si/Al ratio, hence the lowest acid site density. A kinetic bifunctional model, in which the limiting step is the isomerization of olefinic intermediates on the acid sites, accounts for the quantitative changes in the reaction rate versus the hydrogen and n-hexane pressures. Deactivation effects are responsible for the apparent positive effect hydrogen had, under low pressure, on the activity of the PtHMOR samples with high acid densities.