Design of bi-functional Ni-zeolites for ethylene oligomerization: Controlling Ni speciation and zeolite properties by one-pot and post-synthetic Ni incorporation

The design of diverse Ni-zeolites has been performed attempting to control different physico-chemical properties of the zeolite supports as well as the Ni speciation to study their influence on the industrially relevant ethylene oligomerization reaction. In this sense, Ni-containing medium-pore MFI and large-pore BEA zeolites have been synthesized with different particle sizes, Si/Al molar ratios and following different Ni-incorporation strategies (one-pot versus post-synthesis). Characterization techniques reveal the preferential presence of cationic Ni2+ and NiO nanoclusters inside the zeolitic pores when Ni has been incorporated by post-synthesis impregnation or one-pot approaches, respectively. The presence of Ni2+ species, rather than other factors, mainly governs olefin oligomerization under near-ambient pressures, guiding preferentially towards C4-C6 olefins as main products. Crystal size, acidity and/or Ni incorporation methodology, on the other hand, play key roles under high-pressure reaction conditions, resulting in the formation of heavier olefins, especially in zeolites containing less cationic nickel, larger proportion of NiO clusters and higher Brønsted acid site density.