Effect of migration of ZCu(OH) to Z2Cu upon hydrothermal aging on the NH3-SCR reaction mechanism over a Cu-CHA catalyst

In this study, the experiments combined with activity tests and characterizations were conducted to investigate the influence of hydrothermal aging (HTA) on the reactivity of NH3-SCR over a Cu-CHA catalyst. The results showed that the NOx conversion efficiency can reach more than 80% below 225 ℃ in the reaction between NH3 and NO+O2 after hydrothermal aging, but it increases the N2O production. The wave spectrum of in-situ DRIFTs confirmed the notable differences in the NH3-SCR mechanism between Cu species of ZCu(OH) and Z2Cu at the same reaction conditions. The NH3-SCR reaction occurring on ZCu(OH) followed the ‘Langmuir-Hinshelwood’ (L-H) mechanism, where NH3 combined with products that oxidize NO to NO2 via dimerization and disproportionation reactions to produce the key intermediates as NH4NO2 and HONO. However, the entire NH3-SCR on Z2Cu followed the ‘Eley-Rideal’ (E-R) mechanism, in which adsorbed NH3 effectively reacted with gas-phase NO to form H2NNO and then produced N2. [Display omitted] •Migration of ZCu(OH) to Z2Cu prevented the drop of adsorption on Lewis acid sites.•Hydrothermal aging results in the loss of NO adsorption and oxidation capacity.•The Lewis acid sites did not change significantly after hydrothermal aging.