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 celcius 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.