Kinetics of hydro-isomerization ofn-hexane over platinum containing zeolites

Kinetic hydro-isomerization experiments at atmospheric pressure usingn-hexane as reactant were performed. Four zeolites with different pore structures but intrinsically equal acid strength (mordenite, ZSM-5, ZSM-22, and ß) were used. Adsorption and diffusion effects were found to mainly determine the differences in activity of these zeolites. The general observation is that the higher the adsorption enthalpy ofn-hexane, the higher the activity per acid site and the lower the activation energy. The latter effect is not very pronounced when the order of reaction inn-hexane is low. The true activation energy of isomerization with respect to the adsorbed alkoxy state is found to be approximately 125 kJ/mol. ZSM-22 and mordenite were both relatively inactive compared to the other zeolites. In the case of ZSM-22 this was due to pore-mouth catalysis resulting in a 5 to 20% usage of the acid sites. The relatively low activity of mordenite occurs since two-thirds of the acid sites, those located in the side-pockets, are not accessible ton-hexane