Synthesis of NiZn-based paddle-wheel metal-organic framework and its use as a catalytic precursor for ethylene dimerization

Abstract

A bimetallic pillared-layered MOF based on Ni and Zn with improved catalytic activity was synthesized and applied in the ethylene oligomerization reaction. According to the XANES spectra, the MOF possesses Ni in the 2+ oxidation state, a well-known active catalytic precursor in oligomerization systems. In addition, Ni and Zn oxide or metallic species were not identified, indicating the absence of impurity phases. µ-XRF and SEM-EDS techniques showed the homogeneous distribution of Ni and Zn species across the SBUs of the bimetallic MOF. Ni/Zn-MOF was applied in the ethylene oligomerization reaction using EASC as the co-catalyst, and the results were compared to its monometallic counterpart Ni-MOF. The bimetallic material Ni/Zn-MOF obtained a TOF corresponding to 135 ×10³ h⁻¹, which accounts for a 60 % increase in the catalytic activity achieved by Ni-MOF (85 ×10³ h⁻¹) under 15 bar of ethylene in a Parr reactor. Moreover, the results obtained in this work are remarkable compared to literature reports for Ni-based MOFs, demonstrating that the co-catalyst employed plays an important role in the catalytic activity. However, Ni/Zn-MOF showed a lower selectivity to α-C₄ oligomers (36 %) against 58 % obtained by Ni-MOF. According to the reuse tests conducted, the bimetallic MOF can be reused for up to two reactions (under 5 bar ethylene in a glass reactor), although presenting a considerable loss in activity due to the formation of metallic Ni.