Effect of Al-distribution on oxygen activation over Cu–CHA

Abstract

Cu(NH₃)₂⁺-pairs in chabazite (CHA) have been suggested to activate oxygen during low-temperature selective catalytic reduction of nitrogen oxides with ammonia (NH₃-SCR). As charge neutrality requires that each Cu-complex is associated with a framework Al, the Al-distribution may affect Cu(NH₃)₂⁺-pair formation and subsequent oxygen activation. Here, density functional theory calculations in combination with ab initio molecular dynamics simulations are used to explore Cu(NH₃)₂⁺-pair formation and oxygen activation in Cu–CHA. The Al-distribution is found to markedly affect the probability for Cu(NH₃)₂⁺-pair formation. Moreover, the molecular dynamics simulations reveal a low-energy reaction path for O₂ activation and dissociation. The facile O₂ dissociation suggests that Cu-pair formation rather than O₂ activation governs the low-temperature NH₃-SCR activity. The results indicate that precise synthesis of Cu-exchanged chabazite with respect to Al-distribution may enhance the catalytic activity.