The Effect of the Pore Structure of Medium-Pore Zeolites on the Dehydroisomerization of n-Butane: A Comparison of Pt–FER, Pt–TON, and Pt–ZSM5

The catalytic dehydroisomerization of n-butane over Pt–ZSM5, Pt–TON, and Pt–FER was investigated. Pt–ZSM5 showed the highest yield and selectivity to isobutene. Most of the by-products of Pt–ZSM5 were formed by oligomerization/cracking of butene, while acid-catalyzed cracking and metal-catalyzed hydrogenolysis of n-butane were more pronounced with Pt–TON and especially with Pt–FER. Skeletal isomerization of butene and cracking of n-butane are both acid catalyzed. But as the rate of n-butane cracking depends more strongly on the concentration of acid sites than the rate of butene isomerization, low acid site concentrations are beneficial for dehydroisomerization catalysts. The dehydrogenation activity of the Pt–zeolites is not only related to the concentration of accessible metal sites. Pt–FER had the highest dispersion, but the lowest dehydrogenation activity. This is attributed to diffusional constraints in the narrow pores of the large ferrierite crystals.