Influence of zeolite pore structure on catalytic reactivity

The influence of zeolite pore-size and shape on the hydro-isomerization of n-hexane was studied. Computer simulations and kinetic measurements, in combination with Positron Emission Profiling (PEP) experiments have been performed. Results showed that, for zeolites with a Al/Si molar ratio of less than 0.1 acidic protons had the same activity. Differences in reactivity are due to differences in the heat of adsorption. Smaller pores result in a higher steady state concentration of adsorbed substrate and adsorbed alkoxy species. Based on a kinetic model, and using experimental heats of adsorption and theoretical protonation energies, the activation energy of hydro-isomerization of n-hexane was found to be approximately 127 kJ/mol. This is consistent with results of a recent quantum chemical model of reactions catalysed by a zeolite proton.