Linking hydrothermal deactivation of Cu-CHA catalysts for NH3-SCR to dealumination and reduced [Cu2(NH3)4O2]2+ formation

Journal article, 2026

NH3-Selective Catalytic Reduction (NH3-SCR) is a critical technology for controlling NOx emissions from diesel and H2 engines. Cu-exchanged chabazite (Cu-CHA) materials are preferred catalysts for the NH3-SCR reaction thanks to high activity, selectivity and stability under normal operating conditions. However, exposure of Cu-CHA to water at high temperatures (>= 650 degrees C) leads to loss of Br & oslash;nsted acid sites due to dealumination. Here, we have measured the activity and selectivity of hydrothermally aged Cu-CHA. The hydrothermal deactivation is linked to changes in the amount of Br & oslash;nsted acid sites as measured by NH3-Temperature-Programmed Desorption (TPD) and the ability to form the key intermediate [Cu2(NH3)4O2]2+, as probed by NO-Temperature-Programmed Reaction (TP Reaction). The activity decreases rapidly during the first 10 hours of aging, which correlates with a rapid loss of Br & oslash;nsted acid sites. The activity after 10 hours is reduced at a slower rate, which coincides with a loss in ability to form [Cu2(NH3)4O2]2+. The measurements are corroborated by density functional theory based microkinetic modeling. The simulations show that the part of the reaction cycle that occurs over Br & oslash;nsted acid sites in fresh catalysts can occur at a slower rate over silanol nests in the aged catalyst. Roughly half of the activity loss after 100 hours of aging can be attributed to the decrease of Br & oslash;nsted acid sites, whereas the remaining loss can be related to reduced formation of the [Cu2(NH3)4O2]2+ complex.