The catalytic cracking of representative hydrocarbons of naphtha (n-hexane, cyclohexane, and methyl-cyclohexane) over ZSM-5 zeolite catalysts was examined at reaction temperatures ranging from 823 K to 923 K under atmospheric pressure. It was found that the Si/Al ratio of the zeolite affected the product selectivity and conversion. 5In order to investigate the effects of the crystal size of the ZSM-5 zeolites on catalyst lifetime, macro-and nano-scale ZSM-5 (Si/Al = 150) with crystal sizes of 2300 nm and 90 nm, respectively, were used for the cracking of representative naphtha hydrocarbons.In the cracking of naphthenes (cyclohexane and methyl-cyclohexane), coke was readily formed from the beginning of the reaction leading to significant deactivation of the 10 catalyst for the macro-scale ZSM-5. In contrast, the nano-scale ZSM-5 exhibited a high conversion and high light olefins yield with stable activity, regardless of the type of reactant. As a result, the application of nano-scale ZSM-5 zeolites to the catalytic cracking of naphtha was effective and gave light olefins with high yield and excellent stable activity.

The catalytic cracking of model naphthenes (cyclohexane and methylcyclohexane) over ZSM-5 zeolites of different crystal sizes (macro and nanoZSM-5) was examined at reaction temperatures ranging from 748 to 923 K under atmospheric pressure, focusing on the associated reaction rate constants and activation energies. The catalytic cracking was found to follow first-order kinetics with respect to the naphthene concentrations and the activation energies for cyclohexane and methylcyclohexane cracking over nanoZSM-5 were determined to be 119 and 116 kJ/mol, respectively. In order to elucidate the rate-limiting step in the cracking process, the Thiele modulus and the effectiveness factor obtained from cracking over the two ZSM-5 zeolites were evaluated. Cracking with nanoZSM-5 proceeded under reaction-limiting conditions, whereas the reaction over macroZSM-5 at 923 K took place under transition conditions between reaction-and diffusion-limiting. The nanoZSM-5 was applied to the catalytic cracking of model naphtha and the results demonstrated that this catalyst was both effective and stable and generated a high yield of light olefins.