The 26 surface sites that are part of σ selected are presented in Table and highlighted by crosses in Figure ). The selected SG contains surface sites of SAAs associated with the three considered hosts. This means that SAAs based on Cu, Zn, and Pd hosts can activate CO 2 effectively. The geometries of the surface sites in σ selected for the Cu host are bridge, hollow, and long bridge and they are present in the (111), (100), and (110) surfaces. In the case of the Zn host, ontop and bridge surface sites of the (0001) and (0001)-step surfaces are part of σ selected . Finally, for the Pd host, the sites in σ selected are bridge, ontop, long bridge, 4-fold hollow, and fcc-s. These sites are present in the Pd surfaces (111), (100), (110), and (211). Each of these sites is displayed in the ESI Figure . Only two SA chemical elements are contained in σ selected , namely Os and Ir. Overall, the analysis of the systems in σ selected reveals that the electronic and geometric environment mostly provided by bridge sites with Ir and Os SAs are key for CO 2 activation.