A single site catalyst supported in mesoporous UiO-66 for catalytic conversion of carbon dioxide to formate

Artikel i vetenskaplig tidskrift, 2024

Carbon dioxide utilisation strategies are of paramount importance, yielding various products such as methanol and formate. Formate is an excellent hydrogen carrier in fuel cells, making it a highly exploitable chemical on the hydrogen energy storage front. Formate has an energy content that is at least five times greater than that of commercially available lithium-ion batteries. Herein, we have prepared mesoporous metal-organic frameworks (MOFs) (m-UiO-66 and m-UiO-66-NH2), using a Zr-based secondary building unit (SBU) and terephthalate linkers. The MOFs were used to support the half-sandwich (tetrazolylpyridyl)iridium(iii) complex to make single-site catalyst (Ir(iii)@m-UiO-66 and Ir(iii)@m-UiO-66-NH2) for CO2 conversion to formate. Both Ir(iii)@m-UiO-66 and Ir(iii)@m-UiO-66-NH2 exhibited improved activity for CO2 hydrogenation to formate in a heterogeneous system. Ir(iii)@m-UiO-66-NH2 and Ir(iii)@m-UiO-66 had turnover numbers of 3313 and 3076 TON, respectively, under optimized conditions. X-ray photoelectron spectroscopy (XPS) showed possible interaction of the complex with the MOF as evidenced by a downfield shift in the binding energies of the Ir 4f electronic environment. The catalysts showed post-catalysis stability, as confirmed by PXRD, FTIR, and XPS. The Ir 4f binding energies of the materials after catalysis showed an up-field shift confirming the presence of Ir-H species which are the active species for catalysis.