Aseries of gas-phase reactants is used to treat aCuexchanged mordenite zeolite with the aim of studying the influence of the reaction environment on the formation of Cu pairs.The rearrangement of Cu ions to form multimeric sites as af unction of their oxidation state was probed by X-ray absorption spectroscopy( XAS) and also by applying advanced analysis through wavelet transform, am ethod able to specifically locate Cu-Cu interactions also in the presence of overlapping contributions from other scattering paths.T he nature of the Cu-oxo species formed upon oxidation was further crosschecked by DFT-assisted fitting of the EXAFS data and by resonant Raman spectroscopy. Altogether,the Cu I / Cu II speciation clearly correlates with Cu proximity, with metal ion pairs quantitatively forming under an oxidative environment.

The speciation of framework interacting CuII sites in Cu-chabazite zeolite catalysts active in the selective catalytic reduction of NOx with NH3 is studied, to investigate the influence of the Al...

Cu-exchanged chabazite is the catalyst of choice for NO x abatement in diesel vehicles aftertreatment systems via ammonia-assisted selective catalytic reduction (NH 3 –SCR). Herein, we exploit in situ X-ray absorption spectroscopy powered by wavelet transform analysis and machine learning-assisted fitting to assess the impact of the zeolite composition on NH 3 -mobilized Cu-complexes formed during the reduction and oxidation half-cycles in NH 3 –SCR at 200 °C. Comparatively analyzing well-characterized Cu-CHA catalysts, we show that the Si/Al ratio of the zeolite host affects the structure of mobile dicopper(II) complexes formed during the oxidation of the [Cu I (NH 3 ) 2 ] + complexes by O 2 . Al-rich zeolites promote a planar coordination motif with longer Cu–Cu interatomic distances, while at higher Si/Al values, a bent motif with shorter internuclear separations is also observed. This is paralleled by a more efficient oxidation at a given volumetric Cu density at lower Si/Al, beneficial for the NO x conversion under NH 3 –SCR conditions at 200 °C.

Cu-exchanged zeolites are widely studied materials because of their importance in industrial energetic and environmental processes. Cu redox speciation lies at the center of many of these processes but is experimentally difficult to investigate in a quantitative manner with regular laboratory equipment. This work presents a novel technique for this purpose that exploits the selective adsorption of CO over accessible Cu(I) sites to quantify them. In particular, isothermal volumetric adsorption measurements are performed at 50 °C on a series of opportunely prereduced Cu-ZSM-5 to assess the relative fraction of Cu(I); the setup is fairly simple and only requires a regular volumetric adsorption apparatus to perform the actual measurement. Repeatability tests are carried out on the measurement and activation protocols to assess the precision of the technique, and the relative standard deviation (RSD) obtained is less than 5%. Based on the results obtained for these materials, the same CO adsorption protocol is studied for the sample using infrared spectroscopy, and a good correlation is found between the results of the volumetric measurements and the absorbance of the peak assigned to the Cu(I)−CO adducts. A linear model is built for this correlation, and the molar attenuation coefficient is obtained, allowing for spectrophotometric quantification. The good sensitivity of the spectrophotometric approach and the precision and simplicity of the volumetric approach form a complementary set of tools to quantitatively study Cu redox speciation in these materials at the laboratory scale, allowing for a wide range of Cu compositions to be accurately investigated.