Intrinsic activities and pore diffusion effect in hydrocarbon cracking in steamed Y zeolite

In the literature, it has been shown that the hydrocarbon cracking activity of a zeolite particle can be greatly enhanced by steam treatment. The extent of enhancement depends on the process condition. Recently, it has been shown that under conditions where the reaction is dominated by the monomolecular mechanism, the turnover frequency and the intrinsic activation energy for cracking are practically unchanged by steaming. However, a much larger difference in activity can be observed under conditions where bimolecular and oligomeric cracking dominate. Thus, the phenomenon of enhanced activity by steaming can be explained by the possibility that the bimolecular and oligomeric cracking reactions are pore diffusion-limited. Steaming generates defects in the zeolite particle, increases the external surface area for diffusion, which then leads to the large enhancement in the observed activity.