The NH 3 -mediated selective catalytic reduction (NH 3 -SCR) of NOx over Cu-ion-exchanged chabazite (Cu-CHA) catalysts is the basis of the technology for abatement of NOx from diesel vehicles. A crucial step in this reaction is the activation of oxygen. Under conditions for low-temperature NH 3 -SCR, oxygen only reacts with Cu I ions, which are present as mobile Cu I diamine complexes [Cu I (NH 3 ) 2 ] + . To determine the structure and reactivity of the species formed by oxidation of these Cu I diamine complexes with oxygen at 200 °C, we have followed this reaction, using a Cu-CHA catalyst with a Si/Al ratio of 15 and 2.6 wt% Cu, by Xray absorption spectroscopies (XANES and EXAFS) and diffuse reflectance UV-Vis spectroscopy, with the support of DFT calculations and advanced EXAFS wavelet transform analysis. The results provide unprecedented direct evidence for the formation of a [Cu 2 (NH 3 ) 4 O 2 ] 2+ mobile complex with a side-on μ-η 2 ,η 2 -peroxo diamino dicopper(II) structure, accounting for 80−90% of the total Cu content. These [Cu 2 (NH 3 ) 4 O 2 ] 2+ are completely reduced to [Cu I (NH 3 ) 2 ] + at 200 °C in a mixture of NO and NH 3 . Some N 2 is formed as well, which suggests the role of the dimeric complexes in the low-temperature NH 3 -SCR reaction. The reaction of [Cu 2 (NH 3 ) 4 O 2 ] 2+ complexes with NH 3 leads to a partial reduction of the Cu without any formation of N 2 . The reaction with NO results in an almost complete reduction to Cu I , under the formation of N 2 . This indicates that the lowtemperature NH 3 -SCR reaction proceeds via a reaction of these complexes with NO.

A comparative assessment of the accuracy of different quantum mechanical methods for evaluating the structure and the cohesive energy of molecular crystals is presented. In particular, we evaluate the performance of the semiempirical HF-3c method in comparison with the B3LYP-D* and the Local MP2 (LMP2) methods by means of a fully periodic approach. Three benchmark sets have been investigated: X23, G60, and the new K7; for a total of 82 molecular crystals. The original HF-3c method performs well but shows a tendency at overbinding molecular crystals, in particular for weakly bounded systems. For the X23 set, the mean absolute error for the cohesive energies computed with the HF-3c method is comparable to the LMP2 one. A refinement of the HF-3c has been attempted by tuning the dispersion term in the HF-3c energy. While the performance on cohesive energy prediction slightly worsens, optimized unit cell volumes are in excellent agreement with experiment. Overall, the B3LYP-D* method combined with a TZP basis set gives the best results. For cost-effective calculations on molecular crystals, we propose to compute cohesive energies at the B3LYP-D*/TZP level of theory on the dispersion-scaled HF-3c optimized geometries (i.e., B3LYP-D*/TZP//HF-3c(0.27) also dubbed as SP-B3LYP-D*). Besides, for further benchmarking on molecular crystals, we propose to combine the three test sets in a new one denoted as MC82.

The reactivity with a NO/NH3 mixture of Cu‐nitrate complexes formed on the surface of a Cu−CHA catalyst active in the Selective Catalytic Reduction of NOx with NH3 (NH3−SCR) was followed at 50 °C by in situ spectroscopic techniques. The catalyst (Si/Al=15; Cu/Al=0.5) was first exposed to NO/O2 (mimicking the SCR oxidative half‐cycle), mainly resulting in the formation of chelating bidentate framework‐interacting CuII‐nitrates. These intermediates were gradually detached from the framework in the presence of NO/NH3 (or NH3 alone), forming mixed‐ligand mobile [CuII(NH3)3(NO3)]+ complexes, with infrared bands at 1624 (δNH3), 1430 and 1325 cm−1 (monodentate nitrate νNO2asym and νNO2sym, respectively). X‐ray absorption and Diffuse Reflectance UV‐Vis spectroscopies showed that during this transformation the CuII/CuI reduction, observed under similar conditions at 200 °C, hardly occurred. DFT calculations confirmed the stability of nitrate ligands in the monodentate conformation in [CuII(NH3)3(NO3)]+ complexes when solvated by ammonia. The resulting structure was successfully used to fit the corresponding experimental EXAFS spectra. The gradual change of ligands in the CuII coordination sphere was confirmed by the blue shifts of both d-d and Ligand to Metal Charge Transfer bands in Diffuse Reflectance UV‐Vis spectra, with formation of features (27500, 32000 and 38000 cm−1) ascribable to the mixed‐ligand configuration.

In this work, we have computed the exfoliation energy (the energy required to separate a single layer from the bulk structure), the interlayer distance, and the thermodynamic state functions for representative layered inorganic minerals such as Brucite, Portlandite, and Kaolinite, while leaving the more classical 2D transition-metal dichalcogenides (like MoS 2 ) for future work. Such materials are interesting for several applications in the field of adsorption and in prebiotic chemistry. Their peculiar features are directly controlled by the exfoliation energy. In materials without cations/anions linking different layers, the interactions keeping the layers together are of weak nature, mainly dispersion London interactions and hydrogen bonds, somehow challenging to deal with computationally. We used Hartree–Fock (HF) and density functional theory (DFT) approaches focusing on the role of dispersion forces using the popular and widespread Grimme’s pairwise dispersion schemes (-D2 and -D3) and, as a reference method, the periodic MP2 approach based on localized orbitals (LMP2). The results are highly dependent on the choice of the scheme adopted to account for dispersion interactions. D2 and D3 schemes combined with either HF or DFT lead to overestimated exfoliation energies (about 2.5 and 1.7 times higher than LMP2 data for Brucite/Portlandite and Kaolinite) and underestimated interlayer distances (by about 3.5% for Brucite/Portlandite). The reason is that D2 and D3 corrections are based on neutral atomic parameters for each chemical element which, instead, behave as cations in the considered layered material (Mg, Ca, and Al), causing overattractive interaction between layers. More sophisticated dispersion corrections methods, like those based on nonlocal vdW functionals, many body dispersion model, and exchange-hole dipole moment not relying on atom-typing, are, in principle, better suited to describe the London interaction of ionic species. Nonetheless, we demonstrate that good results can be achieved also within the simpler D2 and D3 schemes, in agreement with previous literature suggestions, by adopting the dispersion coefficients of the preceding noble gas for the ionic species, leading to energetics in good agreement with LMP2 and structures closer to the experiments.