Effectiveness of nano-scale ZSM-5 zeolite and its deactivation mechanism on catalytic cracking of representative hydrocarbons of naphtha

• The ZSM-5 zeolites with different crystal size were synthesized.
• Alkane and naphthenes cracking reactions over ZSM-5 were carried out.
• The nano-scale ZSM-5 shows longer catalyst life-time than macro-scale ZSM-5.
• Application of the nano-scale ZSM-5 zeolite was effective for the naphtha cracking.

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. In 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 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.

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