Effect of zeolite pore geometry on isomerization of n-butane

A comparative study of isomerization of n-butane over bifunctional catalyst s based on zeolites with different pore geometry (ZSM-5 and mordenite) and with metal particles located inside and/or outside the zeolite main channel system has been carried out. 1,1,1,3,3,3-hexamethyldisilazane was used in order to obtain catalysts with external Bronsted acid sites poisoned. TPDA, FTIR, TPR and TEM techniques were used to characterize the catalysts. ZSM- 5 catalysts were quite resistant to poisoning, mainly when metal sites were located inside the pore system. However, isomerization activity was virtua lly suppressed for the poisoned mordenite catalysts. It is proposed that th e isomerization via C-8 formation cannot take place inside the one-dimensio nal pore system of mesopore-free mordenite catalysts, but this is nor the c ase for isomerization on ZSM-5. (C) 2000 Elsevier Science B.V. All rights r eserved.