Appraising Multinuclear Cu2+ Structure Formation in Cu-CHA SCR Catalysts via Low-T Dry CO Oxidation with Modulated NH3 Solvation

Cu2+ ions (ZCu2+ (OH)- , Z2 Cu2+ ) are regarded as the NH3 -SCR (SCR=selective catalytic reduction) active site precursors of Cu-exchanged chabazite (CHA) which is among the best available catalysts for the abatement of NOx from Diesel engines. During SCR operation, copper sites undergo reduction (Reduction half-cycle, RHC: Cu2+ →Cu+ ) and oxidation (Oxidaton half-cycle, OHC: Cu+ →Cu2+ ) semi cycles, whose associated mechanisms are still debated. We recently proposed CO oxidation to CO2 as an effective method to probe the formation of multinuclear Cu2+ species as the initial low-T RHC step. NH3 pre-adsorption determined a net positive effect on the CO2 production: by solvating ZCu2+ (OH)- ions, ammonia enhances their mobility, favoring their coupling to form binuclear complexes which can catalyze the reaction. In this work, dry CO oxidation experiments, preceded by modulated NH3 feed phases, clearly showed that CO2 production enhancements are correlated with the extent of Cu2+ ion solvation by NH3 . Analogies with the SCR-RHC phase are evidenced: the NH3 -Cu2+ presence ensures the characteristic dynamics associated with a second order kinetic dependence on the oxidized Cu2+ fraction. These findings provide novel information on the NH3 role in the low-T SCR redox mechanism and on the nature of the related active catalyst sites

An optimized Western blot assay provides a comprehensive assessment of the physiological endoproteolytic processing of the prion protein

15 Pág.The prion protein (PrPC) is subjected to several conserved endoproteolytic events producing bioactive fragments that are of increasing interest for their physiological functions and their implication in the pathogenesis of prion diseases and other neurodegenerative diseases. However, systematic and comprehensive investigations on the full spectrum of PrPC proteoforms have been hampered by the lack of methods able to identify all PrPC-derived proteoforms. Building on previous knowledge of PrPC endoproteolytic processing, we thus developed an optimized Western blot assay able to obtain the maximum information about PrPC constitutive processing and the relative abundance of PrPC proteoforms in a complex biological sample. This approach led to the concurrent identification of the whole spectrum of known endoproteolytic-derived PrPC proteoforms in brain homogenates, including C-terminal, N-terminal and, most importantly, shed PrPC-derived fragments. Endoproteolytic processing of PrPC was remarkably similar in the brain of widely used wild type and transgenic rodent models, with α-cleavage-derived C1 representing the most abundant proteoform and ADAM10-mediated shedding being an unexpectedly prominent proteolytic event. Interestingly, the relative amount of shed PrPC was higher in WT mice than in most other models. Our results indicate that constitutive endoproteolytic processing of PrPC is not affected by PrPC overexpression or host factors other than PrPC but can be impacted by PrPC primary structure. Finally, this method represents a crucial step in gaining insight into pathophysiological roles, biomarker suitability, and therapeutic potential of shed PrPC and for a comprehensive appraisal of PrPC proteoforms in therapies, drug screening, or in the progression of neurodegenerative diseases.H. C. A. was supported by the CJD Foundation, Inc and Alzheimer Forschung Initiative e.V. (grant no.: 19050p); J. C. was supported by Spanish Ministry of Science award (grant no.: PID2021-122201OB-C21) cofunded by European Regional Development Fund. R. N. was supported by the Ministero della Salute (grant no.: RF-2016-02364498).Peer reviewe

Investigation of Low-Temperature OHC and RHC in NH₃–SCR over Cu-CHA Catalysts: Effects of H₂O and SAR

A transient kinetic approach was applied to independently investigate the oxidation half-cycle (OHC) and reduction half-cycle (RHC) of NH3–selective catalytic reduction (SCR) at low temperature (150–200 °C). Three model Cu-exchanged chabazite (Cu-CHA) samples with fixed Cu loading (∼1.8% w/w) and different silica-to-alumina ratios (SARs = 10-17-25) were investigated under dry and wet conditions. We confirmed the following: (i) OHC proceeds via second- and first-order kinetics in CuI and O2, respectively, with O2 (+H2O) alone able to completely reoxidize CuI sites; (ii) RHC proceeds via second- and first-order kinetics in CuII and NO, respectively, according to a Cu/NO = 1:1 stoichiometry. Notably, coupling RHC and OHC rates resulted in an accurate prediction of the steady-state standard SCR conditions, providing the consistent closure of the SCR redox chemistry. Unexpectedly, we revealed the impact of H2O to vary depending on the catalyst formulation. At high SAR, water inhibits the RHC and promotes the OHC. As a result, a limited impact was observed on steady-state deNOx activity, while the Cu-oxidation state was significantly enhanced by H2O. With decreasing SAR, however, the H2O effect on RHC gradually shifts from inhibition to promotion, while the OHC is always promoted. At fixed water content, we revealed the RHC rate to decrease with decreasing Al density, with minor influence observed on the OHC; as a result, a lower deNOx activity was observed upon increasing SAR. Remarkably, the application of transient kinetic analysis to decouple RHC and the OHC greatly facilitated the identification of complex H2O and SAR effects on the global SCR redox chemistry