Fig. 6. Gibbs free energy path for the 2NO + O₂ → 2NO₂ reaction in unconfined spaces (full lines) and in CHA cavities (dashed lines) at 1 bar and 298 K at the level of PBE (Quantum Espresso – ultrasoft pseudopotentials – cut-off energy: 60 Ry) with Grimme-D2 correction to account for van der Waals forces.