Iacobone Umberto, Nova Isabella, Tronconi Enrico, Villamaina Roberta, Ruggeri Maria Pia, Collier Jillian, Thompsett David
Laboratory of Catalysis and Catalytic Processes (LCCP), Dipartimento di Energia, Politecnico di Milano, Via Giuseppe La Masa 34, 20156, Milan, Italy.
Emission Control Department, Johnson Matthey Technology Centre, Blounts Court Road, Sonning Common, Reading, RG4 9NH, UK.
ChemistryOpen. 2022 Sep;11(9):e202200186. doi: 10.1002/open.202200186.
Cu ions (ZCu (OH) , Z Cu ) are regarded as the NH -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 from Diesel engines. During SCR operation, copper sites undergo reduction (Reduction half-cycle, RHC: Cu →Cu ) and oxidation (Oxidaton half-cycle, OHC: Cu →Cu ) semi cycles, whose associated mechanisms are still debated. We recently proposed CO oxidation to CO as an effective method to probe the formation of multinuclear Cu species as the initial low-T RHC step. NH pre-adsorption determined a net positive effect on the CO production: by solvating ZCu (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 feed phases, clearly showed that CO production enhancements are correlated with the extent of Cu ion solvation by NH . Analogies with the SCR-RHC phase are evidenced: the NH -Cu presence ensures the characteristic dynamics associated with a second order kinetic dependence on the oxidized Cu fraction. These findings provide novel information on the NH role in the low-T SCR redox mechanism and on the nature of the related active catalyst sites.
铜离子（ZCu(OH)，Z Cu）被视为铜交换菱沸石（CHA）的NH-SCR（SCR=选择性催化还原）活性位点前体，铜交换菱沸石是用于减少柴油机中NO排放的最佳可用催化剂之一。在SCR运行过程中，铜位点经历还原（还原半周期，RHC：Cu→Cu）和氧化（氧化半周期，OHC：Cu→Cu）半周期，其相关机制仍存在争议。我们最近提出将CO氧化为CO作为一种有效的方法来探测多核铜物种的形成，这是最初的低温RHC步骤。NH预吸附对CO生成有净正效应：通过溶剂化ZCu(OH)离子，氨增强了它们的迁移率，有利于它们偶联形成双核配合物，从而催化反应。在这项工作中，在调制NH进料阶段之前进行的干CO氧化实验清楚地表明，CO生成的增强与NH对铜离子的溶剂化程度相关。与SCR-RHC阶段的类比得到了证实：NH-Cu的存在确保了与氧化态铜分数的二级动力学依赖性相关的特征动力学。这些发现为NH在低温SCR氧化还原机制中的作用以及相关活性催化剂位点的性质提供了新的信息。
