Catalytic Ethylene Oligomerization over Imine-Linked Covalent-Organic Frameworks with Coordinative Ni(II) and Cr(III)

Covalent-organic frameworks (COFs) hold great promise for heterogeneous catalysis due to their porous structure for gas adsorption and tunable functionality for bond activation. This study reports two flower-like shaped imine-linked COFs with coordinative Ni-(II) and Cr-(III) species, to endow Ni/PD-TPA COF and Cr/PD-TPA COF, for catalytic ethylene oligomerization. The synergy between imine nitrogen atoms and coordinated metals enables an exceptional activity (16.70 × 10⁵ and 19.90 × 10⁵ g/(mol M·h)) with high selectivity of butene and hexane (∼98.5%) in long-span catalytic processes, respectively. To optimize multiple reaction parameters (e.g., cocatalyst dosage, temperature, and time), Box-Behnken design (BBD) is employed as a statistical tool to establish a precise model integrating process parameters, catalyst structures, and catalytic performance. The optimized models exhibit high precision (indicated by high <i>R</i> values) in predicting the activity and selectivity of ethylene oligomerization over Cr/PD-TPA COF and Ni/PD-TPA COF, indicating the promise of BBD in reaction engineering and process design. M/PD-TPA COFs are highly active after three recycles and deliver the highest activity at ambient temperature and low pressure with a minimal quantity of cocatalysts compared with other catalysts. These findings demonstrate the potential of metal-loaded COFs for sustainable heterogeneous catalysis and provide insights into the optimization of reaction parameters using statistical methods.