Ethylene Oligomerization: Unraveling the Roles of Ni Sites, Acid Sites, and Zeolite Pore Topology through Continuous and Pulsed Reactions

Herein, four catalysts, consisting of either MFI or BEA as the zeolite framework in the presence or absence of Ni, are compared to explore the individual and collective adsorptive and catalytic contributions of pore topology, Ni sites, and acid sites. Both continuous and pulsed chemisorption/reaction experiments are used to obtain a complete picture of the time-dependent adsorption-desorption behavior, reaction mechanisms, and deactivation steps. The methodology highlights the effect of acid sites, especially during the initial stages of reaction and in the BEA-based catalysts, which have higher acidity at a given Si/Al ratio. In addition, Ni accelerates the reaction and improves the selectivity towards intermediate oligomers. However, the tendency for the most active Ni and acid sites to saturate and deactivate more rapidly than the less active ones may lead to misinterpretation when using the continuous reactor alone. Hence, the dominant mechanisms over the different catalyst sites and reaction times are discussed based on the combined steady and dynamic experiments. Reactive-adsorptive and pulsed-continuous ethylene feeding on MFI, BEA zeolites, and Ni/zeolite catalysts reveal ethylene adsorption and oligomerization steps. The dynamics of these steps (initial and pseudo-steady state) and the impact of zeolite pore topology, Ni, and acid sites on the reaction-adsorption mechanisms are investigated.image

Automated summary

This study compares the effects of different catalyst structures on adsorption and catalysis, exploring the roles of pore topology, Ni sites, and acid sites. The results show that acid sites are particularly important during the initial stages of the reaction, and using a continuous reactor alone may lead to misinterpretation. Ni accelerates the reaction and improves the selectivity towards oligomers. Based on the experimental results, the dominant mechanisms over the different catalyst sites and reaction times are discussed.