Combined Diffusion, Adsorption, and Reaction Studies of n-Hexane Hydroisomerization over Pt/H–Mordenite in an Oscillating Microbalance

Abstract

Uptake experiments under full catalytic conditions have been performed using a tapered element oscillating microbalance. The effect of acid leaching on the diffusivity and reaction of n-hexane in Pt/H–mordenite has been established from these experiments. For acid-leached Pt/H–mordenite the hydroisomerization activity is four times higher than for untreated Pt/H–mordenite. Acid leaching gives rise to an acceleration of the uptake of n-hexane under reaction conditions. Analysis of the data implies the faster uptake to be predominantly accounted for by a shorter intracrystalline diffusion path length, as diffusivities are in the same range for both catalysts. The shorter path length results from the mesoporous structure of H-mordenite generated by acid leaching. From the diffusivities, from the path lengths, and by using the Thiele model, it is inferred that the intrinsic rate constant of acid-leached Pt/H–mordenite is twice that of the untreated Pt/H–mordenite. The facilitated transport of reactants and products doubles the effectiveness factor, thus also contributing to the overall activity enhancement for n-hexane hydroisomerization after acid leaching.