Identifying and Regulating the Active Metal Sites in Heterogeneous Ni-Based Catalysts for Ethylene Oligomerization

Abstract

Ethylene oligomerization is a crucial reaction for the production of higher olefins, for which homogeneous catalysts are currently employed in industry. In recent years, Ni-based heterogeneous catalysts have attracted extensive attention. However, the active species for ethylene oligomerization over such catalysts remain highly controversial. This study investigates the nature of the active sites for ethylene oligomerization over Ni-based catalysts using amorphous silica-alumina as the support. Combining multiple characterizations, it is demonstrated that neither NiO nor metallic Ni0 contributes to ethylene oligomerization. Instead, the active sites are identified as Niδ+ species chelated with the support. Moreover, the acidity of the support plays a critical role in the formation of these active sites. The optimized catalyst achieves a reactivity of 5.44 molethylene·h–1·gNi–1 and a C4–C8 olefin selectivity of 94%. Furthermore, after 55 h of continuous reaction, the ethylene conversion gradually decreased from 64 to 50%, indicating a relatively slow deactivation rate. Subsequent regeneration cycles enabled complete recovery of the initial catalytic performance, demonstrating the regenerability of the catalyst. This work elucidates the mechanism of support acidity in regulating the catalytically active metal sites, providing insights into the design of efficient heterogeneous catalysts for ethylene oligomerization.