Dual-Site Single-Atom Ni Catalysts for Highly Efficient Ethylene Oligomerization to 1-Hexene

The shale revolution has reshaped the global energy landscape, making ethane an efficient feedstock for ethylene production, which has created a market scarcity of higher α-olefins, such as butene and hexene. Therefore, the ethylene oligomerization of abundant ethylene to produce higher α-olefins offers significant advantages. However, substantial challenges remain in enhancing the product separation and catalyst recyclability during ethylene oligomerization. We propose a directed coordination strategy based on covalent organic framework (COF) structures, wherein metal active centers are precisely anchored to yield atomic-level degrees of dispersion within the frameworks. This approach effectively avoids catalyst deactivation induced by aggregation while exposing a higher number of active sites. The highly dispersed single-atom catalyst NPP@Ni exhibits an exceptional activity (10.96 × 10⁵ g/(mol Ni⋅h)^-1) and a high selectivity toward hexene (>66.5%) across multiple catalytic cycles. The rational design of COF topologies enables the systematic regulation of the coordination environments and electronic structures of Ni sites. The catalytic performance and theoretical density functional theory calculations suggest that the coordination environment of Ni correlates directly with the selectivity toward α-olefins. This study provides novel insights into the design of highly efficient and stable ethylene oligomerization catalysts.