Ethylene oligomerization over H- and Ni-form aluminosilicate composite with ZSM-5 and MCM-41 structure: Effect of acidity strength, nickel site and porosity

The micro-mesoporous aluminosilicates with composite structure of ZSM-5 phase encapsulated in MCM-41 structure were prepared. The corresponding H- and Ni-form composites were characterized and compared with the ZSM-5, MCM-41 to investigate the influence of acid strength and porosity on the catalytic performance of ethylene oligomerization. Their acidity increases with the increased ZSM-5 components incorporated in the MCM-41 structure. After loading Ni species the amount of weak acid site increases and that of strong acid site decreases. The interaction between the exchanged Ni-ion and the support is improved by the increased strength of acidity of zeolite. The catalytic character of the ZSM-5 and MCM-41 phase exhibited in the products distribution was studied under two typical reaction conditions for alpha-olefins and liquid fuel productions. The synergetic effect of Ni-ions and acid sites with different acid strength zeolite structure shows that the Ni-ion on MCM-41 is superior for ethylene conversion and determines the Anderson-Schultz-Flory products distribution at 523 K, and the strong acid site from microporous ZSM-5 is preponderant for ethylene conversion and dominates products distribution at 723 K. The nickel species are not only favorable to dimerization of a-olefins at 523 K, but also to dehydrogenation for aromatics generation at 723 K.