Sulfonic acid-modified MOFs as heterogeneous bifunctional catalysts for ethylene oligomerization at room temperature without cocatalysts

Abstract

Ethylene oligomerization plays an important role in industrial production. However, when taking the traditional non-metallocene catalysts and MOF catalysts for ethylene oligomerization, they typically require methylaluminoxane (MAO), aluminum alkyl, and other cocatalysts, which is neither environmentally friendly nor helpful in reducing production costs. Here, three sulfonic acid-modified MOFs (SA/MIL-101(Cr), UiO-66-NS and MIL-101(Cr)-NS) were prepared and used as catalysts for ethylene oligomerization at room temperature without using any cocatalysts. All of them exhibited excellent catalytic performances (e.g., 10SA/MIL-101(Cr), 21 953 g mol_Cr⁻¹ h⁻¹, with C₈ selectivity greater than 70.32%), and their oligomerization activity increased by almost tenfold compared to unmodified MOFs. The presence of Lewis acid (L acid) and Brønsted acid (B acid) sites in modified MOFs is the key to improved performances. In particular, the presence of B acid weakens the role of metal clusters and ligands in MOFs, making it easier for metal centers to bind to ethylene molecules for further oligomerization. This work first demonstrates that bifunctional MOF catalysts can catalyze ethylene tetramerization under mild conditions without cocatalysts.