Activation of oxygen on (NH3–Cu–NH3)+ in NH3-SCR over Cu-CHA

Journal article, 2018

Cu-CHA materials are efficient catalysts for NH 3 –SCR of NO x in oxygen excess. A crucial step in the reaction is oxygen (O 2 ) activation, which still is not well understood. Density functional theory calculations in combination with ab initio thermodynamics and molecular dynamics are here used to study O 2 dissociation on Cu(NH 3 ) 2 + species, which are present under NH 3 –SCR conditions. Direct dissociation of O 2 is found to be facile over a pair of Cu(NH 3 ) 2 + complexes whereas dissociation on a single Cu(NH 3 ) 2 + species is unlikely due to a high activation energy. The presence of NO promotes oxygen dissociation on both single and pairs of Cu(NH 3 ) 2 + complexes. Nitrites and nitrates are easily formed as O 2 dissociates, and NO adsorption over nitrates leads to facile formation of NO 2 . The results stress the importance of ligand-stabilized Cu species in Cu-CHA catalysts for NH 3 –SCR.