Activation of Oxygen and NO in NH3-SCR over Cu-CHA Catalysts Evaluated by Density Functional Theory

The activation of NO by oxygen is a crucial step in the selective catalytic reduction of NO by NH 3 over Cu-CHA catalysts. In this article, the transition states and activation energies for this activation on isolated and neighboring Cu ions are compared by density functional theory calculations, using the nudged elastic band method. For isolated Cu ions, oxygen can be adsorbed both “side-on” and “end-on”. The “end-on” configuration of oxygen reacts with NO to bidentate nitrate via sequential incorporation of the oxygen atoms; the activation energy for this reaction is +1.17 eV. Adsorption of oxygen on two neighboring Cu ions is very favorable, with an adsorption energy of −1.37 eV. Adsorption of NO leads to dissociation of the O–O bond and an NO 2 species is formed on each Cu ion. The activation energy for this reaction (0.60 eV) is lower than that for the activation on isolated Cu ions. This indicates that the SCR reaction on two neighboring Cu ions is faster, which can account for an increased TOF with increasing Cu load in a Cu-CHA zeolite.