Influence of the zeolite structure on the hydroisomerization of n-heptane

Four types of zeolites (Y, β, EU-1, ZSM-22) and a pillared clay, loaded with 1 wt.% of Pt have been studied in n-heptane isomerization. The porous structure of the solid has a strong influence on the isomerization yields. With open structure solids (Y, β, pillared clay), cracking is low at any temperature. The methylhexanes are only converted via protonated cyclopropane. With the more restricted structure solids (EU-1), there is a competition between rearrangements by methyl shift and rearrangements by protonated cyclopropane. Cracking is higher particularly when the temperature increases. On very restricted structure solids (ZSM-22), methyl branching occurs at the pore mouth and the monobranched selectivity is very high.