Combined diffusion, adsorption, and reaction studies of n-hexane hydroisomerization over Pt/H-mordenite in an oscillating microbalance

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. (C) 2001 Elsevier Science.