A computational investigation of the UiO-66 confinement effect on copper clusters: the initial hydrogenation of CO2.

Formate (HCOO) is a key intermediate in CO2-to-CH3OH conversion, especially on Cu-based catalysts. We recently demonstrated how UiO-66 confinement modulates the H2 dissociation capacity of Cu clusters at the electronic level. Nonetheless, an understanding of the direct involvement of UiO-66 moieties (i.e., Zr nodes and organic linkers) in CO2 hydrogenation pathways remains unclear. Here, we investigate the role of UiO-66 moieties in CO2-to-HCOO conversion by comparing non-confined and UiO-66-confined Cun clusters (n = 4, 8, 16, or 32). Three main insights are obtained: (i) the poor activation of CO2 on Cu clusters originates from limited overlap between the Cu HOMO and CO2 LUMO+1; (ii) UiO-66 moieties enhance CO2 adsorption but contribute little to its activation and hydrogenation; and (iii) the confinement effect mainly influences the hydrogenation step by facilitating H-desorption and strengthening C-H interactions.