Appraising Multinuclear Cu 2+ Structure Formation in Cu‐CHA SCR Catalysts via Low‐T Dry CO Oxidation with Modulated NH 3 Solvation

Cu 2+ ions (ZCu 2+ (OH) − , Z 2 Cu 2+ ) are regarded as the NH 3 ‐SCR (SCR=selective catalytic reduction) active site precursors of Cu‐exchanged chabazite (CHA) which is among the best available catalysts for the abatement of NO x from Diesel engines. During SCR operation, copper sites undergo reduction (Reduction half‐cycle, RHC: Cu 2+ →Cu + ) and oxidation (Oxidaton half‐cycle, OHC: Cu + →Cu 2+ ) semi cycles, whose associated mechanisms are still debated. We recently proposed CO oxidation to CO 2 as an effective method to probe the formation of multinuclear Cu 2+ species as the initial low‐T RHC step. NH 3 pre‐adsorption determined a net positive effect on the CO 2 production: by solvating ZCu 2+ (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 NH 3 feed phases, clearly showed that CO 2 production enhancements are correlated with the extent of Cu 2+ ion solvation by NH 3 . Analogies with the SCR‐RHC phase are evidenced: the NH 3 ‐Cu 2+ presence ensures the characteristic dynamics associated with a second order kinetic dependence on the oxidized Cu 2+ fraction. These findings provide novel information on the NH 3 role in the low‐T SCR redox mechanism and on the nature of the related active catalyst sites.