Location of coke on H-ZSM-5 zeolite formed in the cracking of n-hexane

The catalytic cracking of n-hexane was carried out on H-ZSM-5 zeolites. The activity decreased with time on stream due to coke formation. Adsorption measurements with H-ZSM-5 used for n-hexane cracking revealed that coke is deposited on the external surface of H-ZSM-5 crystallites. At low coke amount, that is, at the initial stage of the cracking, only some pore openings are blocked. However, at high coke amount, that is, after a long-time run of the cracking, the pore openings are blocked completely in some crystallites resulting in the deactivation. Therefore, H-ZSM-5 with large crystallite size suffers from the fast deactivation because the number of pore openings is too small to survive the blockage by coke. The rate of deactivation of H-ZSM-5 depends not only on the coke formation rate but also on the crystallite size. (C) 2014 Elsevier B.V. All rights reserved.