n-Heptane cracking on dealuminated HBEA zeolites

n-Heptane cracking was carried out at 450 degrees C over HBEA samples resulting from dealumination of the same parent HBEA zeolite by three different methods: steaming, treatment with solution of hydrochloric acid or ammonium hexafluorosilicate. With all the dealuminated samples, the main reaction products were C3 and C4 alkenes and alkanes (iso/n > 1) which suggests a successive isomerization-cracking process with the participation of a carbocation chain mechanism. Dealumination causes a decrease in the catalytic activity. A linear relation was found between the activity and the square of protonic acid site concentration suggesting that n-heptane cracking is a demanding reaction. A small amount of methane, ethylene and ethane can also be observed, which indicates the participation of the protolytic process in n-heptane cracking. The relative significance of this process depends very much on the method used for dealumination: it decreases with acid and ammonium hexafluorosilicate treatments that eliminates most of the extraframework Al Lewis species and increases with steaming. This suggests that Lewis acid sites play a significant role in the protolytic cracking of n-heptane. (c) 2005 Elsevier B.V. All rights reserved.