Fig. 1. (Left) Proposed reaction scheme for the NH₃-SCR reaction in a Cu-zeolite involving Cu²⁺ and Cu⁺ framework coordinated single cations. Adapted with permission from ref. 49. Copyright 2015 American Chemical Society. The inner blue circle represents the fast SCR cycle. Reactants are indicated in red, reaction products in black, and the proposed NO₂ intermediate in green. (Right) Side view of the chabazite cages showing the Al position in the case with (a) one and (b) two atoms. (a) Is shown with a HONO molecule adsorbed on the Brønsted acid site. (b) Shows a [(Cu²⁺)₂(NH₃)₄O₂]²⁺ complex with two Al atoms situated in one six-membered ring. Atom colour codes: Cu (pink), Si (yellow), Al (purple), O (red), N (blue), and H (white). Adapted with permission from ref. 53. Copyright 2020 American Chemical Society.