The ZSM-5 zeolites with nano

submicron and micron crystal size

denoted as N-ZSM-5

S-ZSM-5 and M-ZSM-5

respectively

were synthesized via hydrothermal method. The effect of crystal size on the product selectivity in catalytic cracking of n-heptane to light olefins reaction was also studied at 510℃ and 650℃

respectively. The results showed that the crystal size of ZSM-5 zeolites had little effect on the n-heptane conversion and the selectivity to olefins at the initial phase at the above two temperatures. At 510℃

however

the submicron and nanometer ZSM-5 zeolites exhibited higher and almost similar selectivity to olefins and stability of reaction activity than the micron sample along with the reaction time. Nevertheless

the N-ZSM-5 zeolite displayed the best performance of selectivity to olefins and stability of reaction activity at 650℃ due to the short diffusion path length and the large external surface area compared to the S-ZSM-5 and M-ZSM-5. The micron-sized M-ZSM-5 zeolite presented the relatively higher selectivity to olefins than the other zeolites

but it also owned the lowest stability of reaction activity at both temperatures. In the catalytic cracking reaction of F-T naphtha

the S-ZSM-5 zeolite gave the best performance of selectivity to olefins and the stability of reaction activity and it may attribute to the complex components of the naphtha materials and their various reaction paths to olefins.