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

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 O-2 activation and dissociation. The facile O-2 dissociation suggests that Cu-pair formation rather than O-2 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.