Fig. 2. Results of MCR-ALS analysis of global temperature-dependent XANES dataset collected for six Cu-CHA samples with different compositions during He-activation from 25 to 400 °C (Fig. 1a), assuming N pure = 5. (a) XANES spectra of pure components μpurei(E) derived from MCR-ALS. The inset reports a magnification of the Cu(ii) 1s → 3d transition region in the theoretical spectra. (b) Temperature-dependent abundance of pure species, wpurei(Cu/Al; Si/Al, T), in each of the catalysts (bars have the same colours as the corresponding spectra in panel (a)). (c) Proposed assignment of the five pure components to specific Cu-species/sites formed in the Cu-CHA catalyst as a function of composition and activation temperature, using the same colour code as in parts (a) and (b). Blue (PC1): mobile Cu(ii)-aquo-complexes [Cu(ii)(H2O) n ]2+/[Cu(ii)(H2O) n–1(OH)]+ with n = 6; green (PC5): Cu(ii) dehydration intermediate, possibly represented by mobile [Cu(ii)(H2O) n ]2+/[Cu(ii)(H2O) n–1(OH)]+ complexes with n = 4; black (PC3): 1Al Z[Cu(ii)OH] sites in their oxidized form; red (PC2): 1Al ZCu(i) sites in their reduced form, resulting from self-reduction of 1Al Z[Cu(ii)OH] species; orange (PC4): 2Al Z2Cu(ii) sites. Atom colour code: Cu: green; H: white; O: red; Si: grey; Al: yellow.
